1. Evidence of evolution suggests that the mechanisms of inheritance, accompanied by selection, allow change over many generations

Outline the impact on the evolution of plants and animals of: changes in physical conditions in the environment, changes in chemical conditions in the environment, competition for resources

Evolution refers to the change in a population over time.

It occurs due to natural selection pressure from a changing environment, which causes a particular trait/characteristic to be advantageous for survival. Within a population, individuals are characterized by a variety of different traits. Individuals with the advantageous traits will survive, breed and pass on these traits to their offspring. Over time, these traits will become more common in the population, thus the population will evolve.

Changes in the physical conditions of the environment

A change in the physical conditions (e.g. temperature or rainfall) will act as a selection pressure for evolution. An example – Peppered Moth:

Before the Industrial revolution of the late 18th century, most Peppered moths occurred in two varieties: a white form and a black form.

The white form was once much more common because it was well camouflaged against the white lichen that covered the trees of its habitat.

As industry developed in the 19th century, however, the bark and lichen were blackened under a cover of soot. The black moth was now better camouflaged and it became more abundant, as the white moths became more vulnerable as prey to birds. So the population of the Peppered moth evolved from mainly white to black.

However, once the government passed various Clean air legislations, levels of soot on the bark declined. As a result, the lighter moths had better camouflage, and the population gradually evolved back to mostly white

Changes in chemical conditions of the environment

A change in the chemical conditions of the environment can have a major effect on the evolution of organisms. Chemicals that can affect evolution include salinity of water/soil and acidity.

An example – Sheep Blowfly, Dieldrin and Organophosphates:

In Australia, the sheep blowfly Lucilia cuprina is a major problem to the sheep industry. It stresses, weakens and can be lethal to sheep when larvae, laid by females, burrows into wounds and wet wool.

Chemicals, such as dieldrin and organophosphates, have been used extensively to control the blowfly.

After the initial success, these agents became less and less effective as the natural resistance led to genetic resistance occurring within the fly population, especially considering the rate of reproduction.

Withholding a particular insecticide for a time allowed the resistance of this particular blowfly population to drop. However, continued use of the insecticide has resulted in the mutation of a modifier gene that increases and maintains the resistance, so the insecticides can never be effective again. Thus, the blowfly population has evolved to be resistant to the chemicals

Competition for resources

Competition for resources, such as access to water, a nesting site or nesting materials have caused species to evolve. Growth habits such as vines are a response to the competition for light. Allelopathy (production of inhibitory chemicals) has evolved in some plants in response for the competition for space.

The introduction of new species to Australia has caused serious competition with native species – leading to many becoming endangered or extinct. An example – Dingo and Tasmanian Tiger:

The introduction of the dingo to the Australian mainland by the Aborigines increased competition for food for the Tasmanian tigers. Dingoes were more efficient predators due to their pack behaviour – so eventually the tiger became extinct on the mainland

Describe, using specific examples, how the theory of evolution is supported by: paleontology (incl. fossils that have been considered transitional forms), biogeography, comparative embryology, comparative anatomy and biochemistry

There are many areas of study that provide evidence for the theory of evolution

Paleontology (including transitional forms)

Paleontology is the branch of science concerned with the fossils of organisms

For some organisms, fossils provide case histories for their evolution. Numerous fossils of the horse have shown its evolution from a small animal about the size of a fox terrier to the modern horse.

A transitional form is an organism that exhibits the characteristics of two different groups of organisms. It provides a link showing the transition from one of these groups to the other. For example, the Archaeopteryx is a transitional form that has characteristics of both reptiles and birds, showing the evolution of birds from reptiles. It has teeth (like a reptile) and feathers (like a bird).

Biogeography

Biogeography is the study of the geographical distribution of organisms, both living and extinct.

The present day distribution of flightless birds suggests that they all originated from a common ancestor on Gondwana. The different populations evolved on the isolated southern continents as they drifted apart. This resulted in emus in Australia, ostriches in South Africa, kiwis in New Zealand.

Comparative embryology

In the early stages of development, the embryos of vertebrates are very similar. They all have gill arches, spinal chords and primitive kidneys. Furthermore, the vertebrate embryos have the same type of skin which later develops into scales, birth feathers, or the hair, claws and nails of mammals. This suggests that the different groups of vertebrates all evolved from the same ancestor

Comparative anatomy

Comparative anatomy is the study of the similarities and differences in the structure (anatomy) of living organisms. For example, limbs of bats, lions and humans are all of similar structure (pentadactyl limb – five fingered), suggesting that these organisms are descended from a common ancestor. However due to different environments, the limbs have evolved differently.

Biochemistry

Biochemistry concerns itself with the chemical processes and substances occurring in living organisms.

Certain biological processes are the same of all living cells. Chemical tests of blood proteins have shown biochemical similarities/evolutionary relationships between animals. Closely related species have only few differences in DNA.

Explain how Darwin/Wallace’s theory of evolution by natural selection and isolation accounts for divergent evolution and convergent evolution

Natural selection describes how organisms that have characteristics that best suit them to the environment survive, reproduce and pass some of these characteristics onto their offspring.

Divergent evolution (evolving to become different)- Darwin/Wallace’s theory of evolution by natural selection therefore suggests that if groups of the same species become isolated, the differing environmental will result in the selection of different characteristics.

Convergent evolution (evolving to become similar) – If two different organisms lie in the same habitat or occupy similar niches, it is likely that over time, the environment will select those characteristics that enable them to survive and the organisms will develop similar structures and physiology.

Analyse information from secondary sources to prepare a case study to show how an environmental change can lead to changes in a species

C. molestus is a species of mosquito that has evolved separate from C. pipiens mosquito. C. molestus live in underground subway complexes whilst C. pipiens live in the day-time streets of London.

C, pipiens live in an environment which experiences fluctuation in temperature and climate throughout the four seasons. Contrastingly the evolved species has been isolated in a subterraneous environment where temperature is warm and virtually constant. This has allowed the mosquitoes to thrive all year round, unlike their counterparts upstairs. Polluted pools of water underground became prime breeding sites for C. molestus. The blood of rats and humans provided nutrition for females, whilst decaying rubbish and human hair/flaked off skin fed the males.

As a result to this complete change in the environment for the underground mosquitoes, they gradually evolved distinctively from C. pipiens, emerging as an entire new species. An experiment by the geneticist Katherine Byre demonstrated that the habits of C. pipiens and C. molestus were entirely different: C. molestus bred all year round, C. pipiens hibernate in winter; and the most importantly the two could not interbreed – indicative of two separate species.

Furthermore, DNA tests revealed that different colonies of mosquitoes of the underground were more genetically similar than to their above-ground counterparts. This demonstrates the importance of environment in instigating and shaping the evolution of a species.

Gather information from secondary sources to observe analyse and compare the structure of a range of vertebrate forelimbs:

They all consist of a forearm bone, connected two a dual lower arm group, connected to wrist bones (carpals in humans) which connect to the digits. Usually 5 in number (pentadactyl).

Pointing to a common ancestor.

Use available evidence to analyse, using a named example, how advances in technology have changed scientific thinking about evolutionary relationships

The development of biological evidence changed the way people thought about evolutionary relationships. This allowed comparisons of organisms where homologous structures were not available and provided a quantitative analysis (where degree of difference can be scientifically measured rather than just based on observation)

In the 1860’s, orangutans, gorillas and chimpanzees were classified as one family and humans were placed in a separate family. This was based on the structural anatomy of the organisms.

However, once amino acid sequencing was used in the 1960s, it was revealed that humans and chimpanzees had identical sequences, whilst there was one amino acid difference between these species and gorillas. Further progress in molecular biology (DNA sequencing/hybridization) confirmed the results of the amino acid sequencing.

The results were: gorillas and chimpanzees were more closely related to humans than orangutans, which diverged much earlier on.

Analyse information from secondary sources on the historical development of theories of evolution and use available evidence to assess social and political influences on these developments

The Age of Enlightenment encouraged people to use reason and personal experience as the basis of knowledge rather than simply accepting those of institutions like the Church and monarchy. This led to thinking becoming more scientific as people began applying reason through experimentation.

In 1809, the French naturalist Jean Baptiste Lamark paved way for evolutionary thinking by proposing his theory of evolution by ‘the inheritance of acquired characteristics’. At that time, France was experiencing an industrial and political revolution which encouraged freedom of thought. Although his theory was discredited, his proposal opened society’s thinking – encouraging people to consider and debate other points of view.

During the Age of Reason, people no longer simply accepted the church’s stance on Creationism. Likewise, Darwin formulated his own ideas through personal observation and reasoning. New ways of thinking were prevalent in society and politics in the 1800s – influencing both Darwin and Wallace in shaping their theory of evolution.

2. Gregor Mendel’s experiments helped advance our knowledge of the inheritance of characteristics

Outline the experiments carried out by Gregor Mendel

Gregor Mendel studied the inheritance of different characteristics in pea plants.

He selected true breeding plants which differed in a particular characteristic and crossed them. The starting plants were known as the parental generation (P1), and the hybrids which result were the first filial generation (F1).

In the F1 generation, all the offspring displayed the trait of one parent (the one containing the dominant gene). Mendel allowed the F1 hybrid plants to grow and self-pollinate, then he collected the seeds and planted a new generation. In the F2 generation, it seemed that the trait from the other parent would arise (appearing to have ‘skipped’ a generation). The ratio of the two traits, on average was about 3:1 (favouring the dominant gene). Mendel then derived principles based on his mathematical calculations.

He worked out the law of dominance and segregation, which states that there are two factors for each characteristic, and these segregate with one factor in each reproductive cell. At fertilization, a factor from each parent is combined into the offspring. These characteristics do not blend; one dominates over the other.

Describe the aspects of the experimental techniques used by Mendel that led to his success

Factors that led to Mendel’s success include:

He studied a suitable organism – peas grow quickly and each generation takes just one season to produce. Mendel was also able to control pollination (using both self-pollination and cross-pollination)

He studied variations that were clear to identify – this made it easier for Mendel to record results of a cross.

He studied one characteristic at a time – this gave him a clearer picture of what was happening. Studying a number of characteristics at the same time would make the results hard to interpret.

He started with pure lines – Mendel made sure that the characteristic he was studying would appear unchanged generation after generation. He allowed the peas to self-pollinate year after year and checked that offspring always showed the desired feature. Organisms which do this are called pure lines.

Describe outcomes of monohybrid crosses involving simple dominance using Mendel’s explanations

A monohybrid cross refers to the breeding of two organisms that have differing alleles for a single trait. It is used to examine just one specific set of alleles/traits.

For example, Mendel crossed a homozygous tall plant with a homozygous short plant. This produces an F1 generation where all of the plants are tall. Mendel explained that the trait exhibited in the first generation was the dominant factor.

Distinguish between homozygous and heterozygous genotypes in monohybrid crosses

Homozygous organisms have identical alleles for a particular trait (ie pure bred).

Heterozygous organisms are hybrid organisms which have differing alleles for a particular trait.

Distinguish between the terms allele and gene, using examples

A gene is a segment of DNA on a chromosome which codes for a particular characteristic.

Different variations of the same gene are termed the alleles of that gene. Within an individual, an allele is one member of a pair located on a specific position on a chromosome. There are only two alleles within the individual; however there can be more than two alternate alleles in a population

For example, the gene for height has two alleles tall (T) and short (t). These versions of the same gene (alleles) are found in identical positions on a pair of similar chromosomes within cells. Haploid cells (gametes) only have one allele for each gene, whilst normal cells (diploid) have two.

Sometimes, there can be more than two alleles for a gene, for example, flower colour in sweat peas can be pink, white purple, red etc.

Explain the relationship between dominant and recessive alleles and phenotype using examples

The genetic-make up or genotype of an organism determines its physical appearance, or phenotype. The genotype is the cause of the way it looks and the phenotype is the effect/result.

When a pair of differing alleles occurs within an individual (heterozygous), only one of the alleles is expressed. This allele is known as the dominant allele. The allele which is not expressed is called the recessive allele.

For example, the allele for the short characteristic in tea plants is recessive. Thus, if the dominant gene (tall) is within the genotype, the phenotype becomes tall.

Recessive alleles can be carried for several generations without being expressed as the phenotype due to the presence of the dominant allele. It may appear in a latter generation only if it occurs in the homozygous recessive form. This is referred to as have ‘skipped’ a generation.

Outline the reasons why the importance of Mendel’s work was not recognized until some time after it was published

Mendel published his work in 1866 at the Publication Proceedings at the Natural History Society of Britain; however it wasn’t recognized for almost 35 years. Reasons why his work was ignored include:

His work was too progressive – there was little background knowledge. Cells, chromosomes, mitosis and meiosis were unknown and studies of genetics did not exist

His work differed radically from previous research. The accepted belief at the time was the ‘blending’ of characteristics in the offspring of contrasting pure-bred parents. Mendel’s use of mathematics and statistics to analyse results and make predictions were different to the norm at the time and may not have been understood

He had no established reputation or recognition in the broader scientific world. As a result, his standing as a scientist could have been doubted

He presented his findings to only a small group of scientists (approx 40) at two meetings. They were both fairly low profile gatherings of scientists

Process information from secondary sources to describe an example of hybridization within a species and explain the purpose of this hybridization

After moving from England to Australia in 1870, William Farrer recognized that wheat-growing in Australia was presenting problems (particularly the English varieties)– the strains being grown were not suited to the harsh, dry environment, were highly susceptible to disease and grain quality was not of a high enough standard.

He noticed that desirable characteristics in introduced wheat varieties:

Indian wheat was drought tolerant and resistant to some diseases Canadian fife wheat matured late and had the best milling and baking qualities

He realized that traits such as these could be inherited as discrete units if pure-bred plants were crossed. He hybridized the two varieties and selected the plants that displayed the advantages of both parents. He then produced many of these hybrids for commercial use in Australia.

3. Chromosomal structure provides the key to inheritance

Outline the roles of Sutton and Boveri in identifying the importance of chromosomes

Walter Sutton and Theodor Boveri independently worked on the chromosomal theory of inheritance, eventually forming the Sutton-Boveri chromosome theory which identified that genes were located on chromosomes.

Boveri investigated the inheritance pattern in sea urchins, and proposed that: not all chromosomes were the same and that a definite set of chromosomes were necessary for the normal development of an organism.

Walter Sutton experimented with grasshoppers, and found that the behaviour of chromosomes corresponded with Mendel’s laws of segregation and independent assortment. He suggested that during the lining up of chromatids at the equator during metaphase was purely by chance (following the law of segregation that pairs of factors separate randomly and independently when forming gametes). For the law of independent assortment, he found that genes would segregate independently if they were on different homologous chromosomes. However, if the genes for two characteristics were on the same chromosome, they would be inherited together –rather than sorting separately according to Mendel’s second law.

He also suggested that during meiosis, the number of chromosomes is halved, and that fertilisation restored the full chromosome number.

Describe the chemical nature of chromosomes and genes

Chromosomes carry genetic information. Each chromosome consists of many genes; each gene is a certain length of the DNA molecule. The DNA is made of sugar, phosphate, and nitrogenous bases (which form the unit of a nucleotide)

Note this process occurs only before meiosis/mitosis. Chromosomes/chromatids do not exist as such during other times.

The DNA is coiled tightly around a protein core (histone proteins) to form nucleosomes (which consist of about 8 histone proteins together with the DNA). The nucleosomes are compressed and coiled to make Chromatin Fibre.

All these fibres compress to form a supercoil chromatid. Ultimately, a chromosome is made up of about 60% protein and 40% DNA.

Identify that DNA is a double-stranded molecule twisted into a helix with each strand comprised of a sugar-phosphate backbone and attached bases – Adenine (A), thymine (T), cytosine (C) and guanine (G) – connected to a complementary strand by pairing the bases, A-T and G-C

DNA (deoxyribonucleic acid) is: A double stranded helix Made up of sub-units called nucleotides, which is made up of a phosphate, a sugar and a

nitrogenous base The sugar is deoxyribose The four different bases are adenine, thymine, guanine and cytosine. Adenine pairs with

thymine (A-T) and guanine with cytosine (G-C) To form the double helix, the dies of the ladder are made up of alternating sugar and phosphate

molecules and the rungs consist of paired nitrogenous bases. The bases attach to the sugar The other strand of DNA attaches to the strand by complementary pairing of the nitrogenous

bases. The other strand is ‘flipped’ (it goes in the opposite direction).

*for information on DNA replication, refer to sheet

Explain the relationship between the structure and behaviour of chromosomes during meiosis and the inheritance of genes

Meiosis is the type of cell division that occurs in sexual reproduction organs of a plant or animal and it results in the formation of gametes (sex cells).

When a cell divides by meiosis it undergoes two successive divisions – meiosis I, where the cell divides into two cells and then meiosis II where those two cells each divide again, resulting in four daughter cells. Each daughter cell has half the original number of chromosomes that the parent cell had. (in humans, 46 chromosomes is the diploid number, gametes have a haploid number (23 chromosomes).

A homologous pair of chromosomes consists of two corresponding chromosomes (which look identical – except for the sex chromosomes): one of the pair is maternal in origin and the other is paternal. In human there are 23 homologous pairs of chromosomes.

The stages of meiosis that lead to the creation of gametes are:

The DNA/chromosomes replicate. The single stranded chromosomes become double stranded, linked at the centre by a centromere.

In the first meiotic division, the homologous chromosomes separate, but the double-strands of the chromosomes are still joined.

Different pairs of homologous chromosomes behave independently of each other and each pair segregates randomly to the daughter cells.

Gene pairs on different chromosomes sort themselves in the same manner as chromosome pairs.

In the second meiotic division, the chromatids of the chromosomes separate and form 4 daughter cells or gametes altogether. Meiosis II does not affect genetic variation

Interphase – replication; Prophase – homologous pairing and crossing over; Metaphase – aligning, segregation; Anaphase - split

Genetic variation:

Crossing over – this occurs only during meiosis I, where the arms of homologous chromosomes exchange genetic material.

Random segregation – also occurs during meiosis I, when homologous pairs separate and align randomly on differing sides.

Through these mechanisms, meiosis creates genetic variation whilst maintaining the constant chromosome number from one generation to the next. It halves the number of chromosomes when gametes are produced, but once the gametes of the father fuse with the mother’s - the full set of chromosomes are restored within the offspring.

Explain the role of gamete formation and sexual reproduction in variability of offspring

Variability in genetics relates to the different forms of a gene (alleles) within a population. Variation is evident in the physical differences between individuals (e.g. colour and height)

Gametes form through meiosis, where recombination of genetic material takes place through crossing-over and random segregation. As a result, this produces gametes that are all genetically different of each other.

Gametes produced by organisms with genetically dissimilar parents (i.e. from sexual reproduction as opposed to self-fertilisation) are likely to differ from each other more than the gametes produced by organisms of self-fertilisation.

Process information from secondary sources to construct a model that demonstrates meiosis and the processes of crossing over, segregation of chromosomes and the production of haploid gametes

*on separate word doc

Describe the inheritance of sex-linked genes, and alleles that exhibit co-dominance and explain why these do not produce simple Mendelian ratios

Mendelian ratios of inheritance apply only in situations where conditions are similar to those studied by Mendel.

However, if genes do not assort independently or do not show dominance, Mendel’s ratios are not obtained.

Mendel’s experiments do not show sex-specific effects and so sex-linked inheritance shows a deviation from Mendel’s expected ratios.

Examples that deviate from Mendel’s ratios are sex-linked inheritance, incomplete dominance and co-dominance.

Sex-linked inheritance: Sex is a genetically determined characteristic. Every cell in the human body contains 23 pairs of chromosomes: 22 pairs of autosomes

(chromosomes that code for general traits within the body) and 1 pair of sex chromosomes (that influence whether they are male or female).

For females, both the sex chromosomes are the same. This combination is called XX. Females have two X chromosomes, and the chromosomes are homozygous (homogametic).

For males, the sex chromosomes are different. The combination is XY. The Y chromosome is shorter/smaller than the X chromosome (heterogametic).

Since the Y chromosome is much shorter than the X chromosome, some characteristics are only coded for by the X chromosome (the X has genes Y does not have), hence becoming a special case for the inheritance of characteristics.

The larger sex chromosome (X in humans) may also carry a few genes that code for non-sexual body characteristics, termed sex–linked genes, since they are physically linked to the sex chromosomes and are inherited together with sexual traits.

Most sex-linked characteristics are recessive. For example Haemophilia:‘H’ is the dominant, normal allele; ‘h’ is the recessive, haemophiliac allele.

Females:o A normal female’s genotype – XHXH

o A carrier female has the genotype – XHXh o A haemophiliac female has the genotype – XhXh Males:o A normal male – XHY (Y chromosome is missing the gene)o A haemophiliac male – XhY

Sex-linked genes in males and females tend to differ in inheritance, since males lack one X chromosome and therefore have only one allele for each sex-linked gene, rather than a pair (like in females).

As you can see for the example, males only have to inherit a single gene to have the characteristic, since there is no dominant gene on the Y to counter its effect.

A single recessive gene has the same phenotypic effect as a single dominant gene.

This is why some sex-linked characteristics are much more common in males than females.

Incomplete dominance: Not all alleles show dominance and recessiveness. Sometimes neither gene dominates; both are expressed in

the presence of each other. If the both alleles are present (heterozygous) blending of

phenotype will occur. For example if a snapdragon (a flower) has a red & white

gene, it will be pink. Co-dominance:

In this case, the two alleles are not dominant over each other. In a heterozygote where two different alleles for the same gene are present, both alleles are

expressed as separate, unblended phenotypes and so they are termed co-dominant. There is no “blending”, the alleles do not mix, but both can be seen since both alleles behave as

dominant alleles because they are both expressed. An example – Roan coloured cattle:o No blending between the genes so there is no pink cattle. o Pure breeding (homozygous) by cattle may have red or white coat colour. o Hybrid individuals (Heterozygotes, which have one allele for red and one for white coat colour,

have a roan appearance – both red and white hairs are present.

o Looking at the cross in the form of a Punnett square, we can see that a cross concerning a co-dominant trait does not give the simple Mendelian ratio of 3:1

o The cross between the two roan cows of the F1 generation does not give the 3:1 ratio because a heterozygous animal does not give the dominant trait, as would happen in simple dominant-recessive cases. A “heterozygous” animal gives the roan colour, which results in the 1:2:1 ratio.

Describe the work of Morgan that led to the understanding of sex-linkage Thomas Hunt Morgan studied the breeding of the fruit fly, Drosophila melanogaster. As he was breeding the flies, he noticed one white-eyed male fly among the offspring of red-

eyed parents; this was strange as the normal colour was red. Morgan began with a series of crosses in Mendelian sequence to determine if the white gene

showed Mendel’s ratio:1. He cross-bred pure-breeding parents (white-eyed male and pure-bred/homozygous red-

eyed female) to obtain F1 hybrid offspring. 2. He crossed F1 hybrid to obtain F2 generation and expected to see Mendel’s 3:1 ratio but

instead more than 80% flies had red eyes and less than 20% had white eyes. In addition all the flies with white eyes were male; making him believe females could not have white eyes (1st hypothesis).

3. He crossed a white-eyed male with a hybrid red-eyed female. His F2 showed that both males and females can have white eyes.

He hypothesised that the characteristic was ‘sex-limited’, and that it was on the X chromosome. He followed this up with subsequent genetic crosses that proved that red eyes were in fact sex-

linked (carried on a sex chromosome). Morgan’s experiments gave significant evidence needed scientists before they could finally

accept Sutton and Boveri’s chromosome theory of inheritance (that more than one factor/trait was present on each chromosome).

Morgan’s experiments showed that: The gene for eye colour in fruit flies is located on the X chromosome

Hereditary factors can be exchanged between the X chromosomes of an individual

Explain the relationship between homozygous and heterozygous genotypes and the resulting phenotypes in examples of co-dominance

In simple dominance cases, if an organism is homozygous dominant, the phenotype is obviously that of the dominant allele. If it was homozygous recessive, then the phenotype would be that of the recessive allele.

If the organism was heterozygous, then the dominant allele would be the phenotype of the organism, as the dominant allele would preside over the recessive one.

However, if it was a case of co-dominance, heterozygous organisms would have both phenotypes expressed at the same time, as no allele is totally dominant over the other (i.e. red and white alleles in cattle – roan cattle).

Outline ways in which the environment may affect the expression of a gene in an individual

Genes are not the only factor that influences phenotype. The environment is important because it allows for the full expression of genes. The environment can control to what extent a genotype is expressed.

Examples:Hydrangeas: This flower’s colour is controlled by pigments known as anthocyanins. These are affected by pH. If the hydrangeas grow in acidic environments, the flowers will be bright blue. In alkaline environments, the flowers are pale-pink, or off-white.Humans: A young boy in Sydney and a young boy in North Africa who have widely differing genes and environments. There are of course individual differences, but many Australian children have genes for medium length bones and strong muscles whereas many North Africans’ genes code for longer bones and less muscle. The Sydney boy will more than likely achieve the maximum bone length and muscle strength allowed for by his genes. The North African boy is less likely to achieve his genetic potential.

This is because the Sydney environment is more favourable than that of North Africa. There is more chance of optimal growth in Sydney (i.e. nutrition).

Nutrition is of course only one aspect of the environment. Other factors include socio-economic background, oxygen deprivation at birth, peers and traumatic events such as deaths or accidents.

Identify data sources and perform a first-hand investigation to demonstrate the effect of environment on phenotype

Aim: To examine the effect of light on the colour of wheat seedlings.

Hypothesis: The availability of light will change the colour expressed by the plants.

Materials/equipment:

120 wheat seeds 12 Petri dishes Aluminium foil Plastic trays Clear plastic wrap Cotton wool

Variables:

Independent Control Dependent Availability of light Temperature

Humidity Water Same amount and type of seedlings (all

genetically similar) Same number of seeds

Colour phenotype

Method:

1. Prepare 12 Petri dishes with 10 wheat seeds (in each) and fill the base with cotton wool (to act as soil).

2. Add about 5-10mL of water to each dish. 3. Place 6 of the Petri dishes into a plastic tray and the other 6 into another one. 4. Seal one of the trays with plastic wrap and the other one with aluminium foil. 5. Leave the plants in a room under the same variables for 24-48 hours. 6. Observe and record results. 7. Remove foil and replace with plastic wrap. 8. Leave for another 24-48 hours and observe changes.

Results: Wheat that was under the aluminium foil was yellow in colour but grew exactly the same as the wheat under the plastic wrap. After the foil was removed, it turned green once exposed to light and left for 24-48 hours.

Discussion: In the absence of light the organism reduces the production of chlorophyll eventually leading to the deactivation of the gene, hence the lack of chlorophyll results in a yellow colour. However, once organisms are re-exposed to light, the plant begins to produce chlorophyll to use this light for photosynthesis, allowing the plant to become green without a change in genome or genotype.

Conclusion: Environment alters the phenotype of an organism, in this case the availability of light, determined the colour of the plant.

4. The structure of DNA can be changed and such changes may be reflected in the phenotype of the affected organism

Describe the process of DNA replication and explain its significance

DNA replication involves the production of two identical double stranded molecules of DNA from one original double helix molecule.

The DNA molecule is unzipped into two separate strands, each half acting as a template for a new chain. This separation is catalyzed by the enzyme helicase (which breaks the original H-bond between base pairs)

Free nucleotides floating in the nucleus attach to the exposed bases (complementary bases join up)

The joining of nucleotides together is catalyzed by DNA polymerase

As a consequence of replication:

A cell can undergo cell division (mitosis), where identical copies of genes can be made with each of the resulting cells having a complete copy of the genetic material of the original cell

Genetic information can be passed on from one generation to another (meiosis)

Explain the relationship between proteins and polypeptides

Proteins are large, complex macromolecules made up of one or more long chains called polypeptides. Each polypeptide consists of a linear sequence of many amino acids joined together by peptide bonds (these chains can go up to 300 amino acids long). One or more polypeptides can be twisted together into a particular shape, resulting in the structure of a protein.

Outline, using a simple model, the process by which DNA controls the production of polypeptides

In order for a cell to make proteins, only the relevant instructions for those proteins are accessed in the DNA nucleotide sequence. But, as the DNA must remain in the nucleus, an intermediate molecule messenger RNA (mRNA) is created. It creates a transcribed copy of the relevant instructions from the nucleus to the ribosomes in the cytoplasm. The ribosomes basically translate the information carried by the mRNA into a cell product (e.g. a protein)

Transcription

In the nucleus, part of the DNA molecule unzips. Free RNA nucleotides then pair up with one strand of the exposed bases. As the RNA nucleotides pair up with their complementary ones, the resultant molecule is known as m-RNA (messenger RNA). The m-RNA leaves the nucleus through the nuclear pore and enters the cytoplasm. It then travels to the ribosome where translation occurs.

Translation

In the cytoplasm, there are free amino acids and t-RNA (transfer RNA) molecules. Once the m-RNA molecule attaches itself to the ribosome, the t-RNA attaches its anticodon (base triplet) to the complementary codon (base triplet) on the m-RNA. A specific amino acid bonds with the t-RNA on the other side of the molecule (t-RNA with a particular anticodon are always loaded with one specific amino acid). A second t-RNA anticodon then joins itself to the second codon on the m-RNA, bringing a second amino acid which bonds with the first through a peptide bond. A third t-RNA molecule joins, and the first one leaves, and the ribosome continues to move along the m-RNA. Note that only six bases (two codons) are exposed in the ribosome at any given time. The polypeptide chain continues to grow until a ‘stop codon’ is exposed on the ribosome.

*for a more detailed model, attach classwork sheets

*Explain how mutations in DNA may lead to the generation of new alleles

A mutation is a change in the genetic material of the cell (a change in the sequence of nucleotides in DNA).

As a result of a mutation, new amino acids will be introduced in the polypeptide chains, this sill lead to new proteins being produced, and new forms of traits. As a result, the generation of new alleles occurs.

Discuss evidence for the mutagenic nature of radiation

Mutagens are environmental factors that cause mutations. The process of inducing a mutation is termed mutagenesis. There are many mutagens known, including:

Chemical mutagens (alcohol, tar in tobacco) Biological mutagens (some viruses and micro-organisms) Mutagenic radiation (ionizing radiation – radioactive material from nuclear reactions such as

radiation from atomic bombs, spills like Chernobyl, and radiation used in medicine. Furthermore, there is a natural source of UV radiation in sunlight)

Evidence for mutagenic nature of radiation:

UV radiation has been found to increase the incidence of skin cancers in humans. In areas where the ozone is thinner (which results in higher UV radiation exposure), there is also a higher incidence of skin cancer.

Many of the early radiotherapists (scientists studying radiation), did not know the dangers of radiation, and were exposed to large amounts of radiation over prolonged periods of time. This led to the development of various illnesses, and eventually death. For example, Marie Curie worked with ionizing radiation for most of her careers and died from leukemia due to overexposure to radioactive emissions.

Many of the survivors of the 1945 bombing of Hiroshima suffered physical mutations as a result to the radioactive output from the nuclear explosion

Victims of the nuclear meltdown in Chernobyl have suffered high levels of infertility and genetic mutations, as well as non-cancerous side effects such as cardiovascular and respiratory conditions

Explain how an understanding of the source of variation in organisms has provided support for Darwin’s theory of evolution by natural selection

Mutation is a fundamental source of all variation. The understanding that mutations affect the base sequence of DNA allows us to understand how they can be passed on from one generation to the next. It supports Darwin’s theory of evolution because it provides a mechanism to explain how heritable variation arises.

If mutations can be inherited, they provide the variation upon which natural selection acts, in order for evolution to occur. Therefore, for evolutionary purposes, a mutation can be redefined as a heritable change in the genetic material.

Apart from genetic mutation, genetic variation also comes from:

Random segregation during meiosis Crossing over during meiosis

Describe the concept of punctuated equilibrium in evolution and how it differs from the gradual process proposed by Darwin

Punctuated equilibrium proposes that, instead of gradual change, there have been periods of rapid evolution followed by long periods of stability (equilibrium). It was proposed by Gould and Eldridge in 1972.

Darwin’s ‘gradualism’ (1858) Punctuated equilibrium Darwin proposed evolution as occurring

gradually within a species over an extended period of time by natural selection

Living things evolved by short bursts of rapid change, followed by long periods of equilibrium (stability)

Although punctual equilibrium and Darwin’s theory of gradualism both yield a similar result, it the process by which the evolution occurs that is different. Many fossil records indicate that organisms evolve suddenly, and then remain stable for millions of years. However, Darwinists use transitional forms to support their idea of ‘gradualism’.

Analyse information from secondary sources to outline the evidence that led to Beadle and Tatum’s ‘one gene – one protein’ hypothesis and to explain why this was altered to the ‘one gene – one polypeptide’ hypothesis

In 1941, George Beadle and Edward Tatum worked on mutants of a fungus mold (Neurospora crassa) – leading to their discovery that genes provide instructions for making proteins.

Beadle and Tatum hypothesized that if there were a one-to-one relationship between genes and specific enzymes, it should be possible to create genetic mutants that were unable to carry out specific enzymatic reactions. They exposed spores of the Neurospora bread mold to X-ray and UV radiation and studied the resulting mutations. Unlike their normal counterparts, the mutants could not live without the addition of particular amino acids to their normal food. The mold had lost the ability to make the enzyme required to create certain amino acids as the corresponding gene had been mutated.

As Beadle and Tatum had predicted, they created single gene mutations that incapacitated specific enzymes – so that the mold with these mutations could not produce enzymes normally produced. This led them to the one gene/one enzyme hypothesis (stating that each gene is responsible for building a single, specific enzyme). Later it was demonstrated that other proteins besides enzymes were also encoded by genes – and they changed to the ‘one gene – one protein’ hypothesis.

Subsequent work led to the realization that certain proteins consist of more than one polypeptide chain. As a result, they discovered that that one gene is not necessarily responsible for the structure of an entire protein – only for a polypeptide chain within. As a result, the current ‘one gene – one polypeptide’ hypothesis was adopted.

Process information to construct a flow chart that shows that changes in DNA sequences can result in changes in cell activity

If there is a simple substitution for a single base pair on a strand of DNA, then this will result in a different amino acid codon forming a different polypeptide. If one base pair is lost from the sequence, there will be a shift along the DNA molecule producing different polypeptides. The following flow chart shows the reaction if thymine is lost from the start of a DNA sequence

Cell activity is controlled by enzymes, which are proteins (i.e. formed by chains of polypeptides). If the chain of amino acids is not in the right sequence, the enzyme will not be functional. In this case, there is a premature stop.

Process information from secondary sources to describe and analyze the relative importance of the work of: James Watson, Francis Crick, Rosalind Franklin, Maurice Wilkins in determining the structure of DNA and the impact of the collaboration and communication on their scientific research

Rosalind Franklin

Rosalind Franklin carried out X-ray crystallography to obtain X-ray diffraction patterns of DNA that were much sharper than were previously obtainable. Her analyses suggested that DNA could be helical in structure. Thus, Franklin did the key experimental work which subsequently allowed Watson and Crick to fully determine the structure of DNA.

Maurice Wilkins

Maurice Wilkin and Rosalind Franklin were colleagues who worked in the same laboratory on the same project; however, they did so independently. This was due to their strained relationship, partly due to the level of competition between them as well as the fact that Wilkins did not look upon Franklin as his equal in a male-dominated scientific community. Without the permission or knowledge of Franklin herself, Wilkins presented Watson and Crick with her X-ray crystallography photographs of DNA, which ultimately allowed them to produce their now famous model.

James Watson/Francis Crick

Unlike Franklin and Wilkins, Watson and Crick had a good relationship and worked closely with each other. Together, they developed a model of the structure of the DNA molecule by combining existing knowledge of the chemical nature of the DNA molecule with the information gained from Franklin’s X-ray diffraction studies.

Individually, Crick had developed mathematical methods of interpreting X-ray patterns of protein helices (like that depicted in Franklin’s work), whilst Watson made the important realization that adenine-thymine and guanine-cytosine formed pairs, which served as the rungs on the twisting ladder of DNA.

The Watson - Crick Model of DNA shows a double helix in which the two chains, composed of alternating sugar and phosphate groups, are bonded together by hydrogen bonds between A-T and C-G. This model has been consistently supported by later research, and has received general acceptance. Watson and Crick’s role in determining the structure of DNA was extremely important as they essentially ‘fit the final pieces together’, producing a 3-D molecular model of DNA which detailed its components and structure.

Collaboration and communication

Although they were colleagues working in the same lab on the same project, there was limited collaboration or communication between Franklin and Wilkins due to their strained relationship. Franklin kept her results secret (working on her own), which may have caused her not to be able to publish or discover aspects as quick as the collaborative effort of Watson/Crick. Perhaps if Franklin, Wilkins, Watson and Crick had all collaborated together, the DNA structure would have been discovered earlier.

In contrast, Watson and Crick maintained a good relationship, and therefore had extension collaboration and communication whilst performing their research. This close collaboration involved extensive sharing of their knowledge on different aspects of the DNA research – allowing them to quickly identify problems with initial DNA models and assumptions. They also discussed ideas with colleagues working in similar fields (and used research available to them such as that of Wilkins obtained from Franklin), providing them with a large pool of information on DNA based both on their own findings and that of other people. Ultimately, their effective collaboration and communication enabled them to determine and publish their DNA model first, before Franklin.

Process and analyse information from secondary sources to explain a modern example of ‘natural’ selection

Peppered moths

There were two observed varieties of peppered moths in industrial England, one black and one white in colour

The white moths were initially more common as they were well camouflaged by lichen on trees. However, as industries developed across England, 19th century soot began to build up on trees and turn their bark into a darker colour. This resulted in white moths being eaten by birds (as

they were no longer camouflaged) and black moths surviving to reproduce at a higher rate, passing on the desired characteristic of a black colour.

In the mid-20th century, controls were introduced to reduce air pollution and this lead to tree trunks becoming cleaner and lichen growth increased. Once again, the white peppered moths were camouflaged and now their white colour became a favourable characteristic. Natural selection quickly lead to white peppered moths being more common again.

5. Current reproductive technologies and genetic engineering have the potential to alter the path of evolution

Identify how the following current reproductive techniques may alter the genetic composition of a population: artificial insemination, artificial pollination, cloning

Artificial insemination

Artificial insemination in animals involves taking sperm from a male and artificially introducing it to a female. This process results in a reduction in genetic diversity because one stud male may be used to father hundreds or thousands of offspring – resulting in a greater than normal percentage of its genes being exhibited within a population.

IVF (In Vitro Fertilisation) in humans differs from artificial insemination in that the egg is fertilized by a sperm outside the mother’s body (e.g. in a Petri dish). This allows some couples that would otherwise be sterile to reproduce. However, if the infertility were genetic, then the genes that cause the infertility may be passed on to the offspring and continue to be in the population.

Artificial pollination

Artificial pollination involves taking the pollen from one plant and placing it on the stigma of another flower. From this, the genetic composition of a population can be rapidly changed to suit the breeder’s desires/requirements.

Cloning

Cloning is the method of producing genetically identical organisms. Plants can be cloned through simple methods like grafting and cutting techniques. More recently, techniques have been used to clone animals (e.g. Dolly the Sheep) If many clones are produced from one parent organism, the genetic variability of the population would be greatly reduced as the cloned organisms would have identical DNA.

Outline the processes used to produce transgenic species and include examples of this process and reasons for its use

Transgenic species are organisms which have had genetic material from a different species transferred into their genetic code. The transgene (i.e. the gene introduced from the foreign species) can be passed on to offspring during reproduction.

Process used:

The process used in producing a transgenic species typically involves: ‘cutting’, ‘copying’ and ‘pasting’:

1. Cutting: A gene for a favorable characteristic is removed from the cell of an organism (using restriction enzymes)

2. Copying: Multiple copies are made (known as ‘gene cloning’) – This step is usually carried out for bacteria

3. Pasting: The genes are inserted (injected) into the egg cell of another species. After fertilization, the gene becomes part of the new organism’s DNA.

4. The egg develops into a mature organism (transgenic species) with the new gene.

Specific techniques:

The main way of cutting/isolating genes:

Special enzymes, called restriction enzymes are used to isolate the useful gene.

There are four main ways of inserting the desired gene into a species:

Micro-injection of DNA directly into the nucleus of a single cell (performed under an optical microscope to introduce DNA into egg cells when creating transgenic species)

Biolistics: involves using ‘particle guns’, where microscopic particles containing DNA are fired from a gene gun into target tissues and cells.

Electroporation: increasing membrane permeability by applying an electrical current. The piece of DNA can then be injected through other means.

Transduction by a viral vector: DNA may be carried by vectors. These viral vectors may be directly injected into the bloodstream or may be delivered by aerosol delivery (e.g. nasal spray)

Example: Transgenic cotton (BT cotton plants)

BT cotton is an example of a transgenic organism.

Process used:

1. Normal cotton seedlings are cut into small pieces and placed into a solid growth medium, where they grow into calluses. The callus cells are then transferred into a liquid medium where they are given hormones so they can grow into cotton plant embryos.

2. The BT gene is extracted from a bacterium Bacillus thuringiensis, using restriction enzymes3. The BT gene must then be transferred to the embryos using a vector bacteria. The embryos are

dipped in a solution (containing the vector and the extracted BT genes, and the vector bacteria inject the BT genes into the cotton cells

4. Once the gene is inserted, the embryos are grown in tissue culture, then placed in a solid medium and germinated into small plants. These plants are now a transgenic species.

Reasons: The main reasons for producing Bt cotton plants are:

It displays increased resistance to pests It decreases reliance on chemical pesticides (beneficial to environment)

Over the years, traditional pesticides used in cotton plants needed to be made stronger and applied more often to eradicate insect pests caterpillars of the Helicoverpa zea moth. With increased sprayings, the caterpillars were building up immunity to the pesticides due to natural selection.

BT cotton plants were genetically modified to contain a gene that codes the production of a protein that kills the caterpillar. This has reduced the need to use pesticides to kill off these caterpillars, which is beneficial to the environment and reduces the development of pesticide resistance (by natural selection).

Discuss the potential impact of the use of reproduction technologies on the genetic diversity of species using a named plant and animal example that have been genetically altered

The main concern with the use of reproduction techniques is that it can cause significant decrease to the natural diversity and genetic variation within populations (although in some cases, the techniques can increase genetic diversity for a short period of time)

Plant example

The use of artificial pollination to create wheat hybrids (hybridization within a species, which produce fertile offspring): crossing Purple Straw variety and Yandilla wheat variety to create a new variety called Federation.

The creation of hybrids initially increases genetic diversity, as new combinations of alleles are being introduced into the gene pool of the population. However, in the longer term, the continued breeding of the same hybrid lines (due to its desirable characteristics) would decrease genetic diversity. As a result, they are less likely to be able to survive sudden environmental change or disease – due to the limited genetic variation.

Animal example

Cloning has been used in agricultural animals in order to precisely control and reproduce certain characteristics in an individual. For example, the cloning of the Japanese black beef bull using cell nuclear transfer provides a rapid way of improving the quality of meat in cattle rather than relying on selective breeding techniques like artificial insemination.

Cloning decreases genetic diversity in populations, as organisms produced are derived from only one parent, thus being genetically identical to the parent. If many clones are produced from only several parent organisms, genetic diversity would be greatly reduced and the cloned organism would become the predominant organism. Gene combinations (that are beneficial to the animal’s survival) that would otherwise be naturally selected will gradually disappear, being replaced by the characteristics we desire (yet may not be of survival advantage to the animal). Thus, this reduction of the gene pool would mean that the population is less likely to survive sudden environmental changes or disease.

Overall discussion

Modern reproductive techniques gives humans the potential to alter the path of evolution, as we artificially combine the characteristics of organisms beneficial to us, rather than for the organism’s survival (as occurs through natural selection). As a result, natural selection no longer drives evolution. In the long term, the use of reproductive technologies to produce large numbers of organisms with the same characteristics decreases biodiversity and genetic variation – leaving them vulnerable to extinction.

Process information from secondary sources to describe a methodology used in cloning

Somatic cell nuclear transfer (SCNT) involves three animals: one donating the nucleus, one acting as an egg donor, and one that plays the role of a surrogate mother. Ian Wilmut and his team used SCNT to create Dolly the Sheep.

1. Cells were taken from the udder of sheep 1. They were starved of nutrients to stop division. 2. The haploid nucleus was removed from an unfertilized egg (enucleation) of sheep 2. The rest of

the cell was left in good working order3. The udder cell was injected into the enucleated egg. The two cells were then ‘zapped’ with

electricity, causing the cells to blend together and the now ‘fertilized egg’ could undergo normal growth through mitosis.

4. As the cells continued to divide via mitosis, the ‘embryo’ was implanted into the uterus of a third sheep. The embryo grew and was born as a genetically identical twin to sheep 1.

Analyse information from secondary sources to identify examples of the use of transgenic species and use available evidence to debate the ethical issues arising from the development and use of transgenic species

Examples of transgenic species include:

BT cotton plants – used to produce cotton. The plant naturally produces chemicals that kill insect pests, thus reducing the need for chemical spraying.

Cold strawberries – these strawberries exhibit cold resistance. A gene from salmon that allows it to survive cold temperatures has been isolated and inserted into the strawberry.

Bacterial insulin – the gene for insulin production (from the human pancreas) have been injected into the DNA of a bacterium. The bacteria then provides mass production of insulin

Ethical debate:

For AgainstEnvironment/nature

- If we are able to produce products that are of benefit to humanity, it would be unethical not to develop them

- Ethical questions regarding us tampering with nature and genetic material.

- Variation in gene pool may be reduced

- Changing the process of evolution through natural selection

Financial - Producing transgenic crops that are more drought-tolerant and resistant to pests give farmers higher yields per season. Furthermore, the quality of the crops could be improved

- Patenting and ‘ownership’ of certain technologies could mean single companies gain a monopolistic right to beneficial GM species.

Health - Foods with higher nutritional value may be developed (particularly important for third-world countries where there are food shortages)

- Potential long-term health risks are GM products are not yet known

- People may have allergic reactions to foods they could previously eat, if those foods contain DNA from another organism

Animal and human rights

- GM crops can be used to solve food shortages in third world countries

- Vegetarians may unknowingly eat good with animal DNA