INHERITANCETopic 3 - 2015

Year 10 Biology

TOPIC 3 – INHERITANCE

Things to cover:1. Review of Topics 1-4

2. Genes & alleles

3. Heterozygous & homozygous

4. Genotypes & phenotypes

5. Dominant traits & recessive traits

6. Autosomal & sex-linked traits

7. Mutations

8. Pedigrees

Work to do:1. Activity – Pedigree – A Family Tree

2. Textbook Qs – Ex2.5 – p77 – Q1-2, 8-9

3. Textbook Qs – Ex2.6 – p82 – Q6-7, 17-19

4. Textbook Qs – Ex2.8 – p92 – Q3-5, 8-10, 11, 13

Ideas to know:

Gene

Allele

ABO blood grouping

Homologous chromosomes

Gametes

Heterozygous

Homozygous

Dominant

Recessive

Base substitution mutation

Frameshift mutation

Insertion

Deletion

Genotype

Phenotype

Complete dominance

Co-dominance

Carrier

Punnett square

Monohybrid cross

Pedigree chart

Gender bias in pedigrees

Generation skipping in pedigrees

Sex linkage

Haemophilia

Colour blindness

REVIEWTopic 1

• DNA is composed of ____________________ .• Each nucleotide consists of:

− A ____________________ sugar − A ____________________ group− A ____________________ base (_____ types)

• The nucleotides form chains. Two chains twist to form the ____________________ shape of the DNA molecule.

• Chemical bonds hold the DNA molecule together. Strong ____________________ bonds hold the nucleotides together, while weak ____________________ bonds form between the bases.

Topic 2

• DNA is coiled up tightly to form _______________ • There are _______________ of chromosomes in every cell.• Most of these are _______________ , controlling general characteristics.• One pair are the _______________ , controlling both sexual and general characteristics.

• Cell division is necessary for ____________________, ____________________ and reproduction.

• One type of cell division, ____________________, is used in the formation of new body cells. It is also used by unicellular organisms for ____________________ reproduction. The __________ daughter cells formed are ____________________ to the parent cell and have __________ chromosomes.

• The other type of cell division, ____________________, is used to form sex cells. Another name for the products of this type of division are ____________________ This process takes place in the reproductive organs. The __________ daughter cells formed are ____________________ to the parent cell and have __________ chromosomes. They are also ____________________ in size.

• In order for cell division to occur, the DNA must ____________________ and the chromosomes must divide equally between the cells.

• ____________________ can occur if this does not happen correctly. For example, disorders involving additional or missing ____________________.

• Down Syndrome is one example. This disorder results from the presence of ____________________ Chromosome 21. This is called ____________________ 21.

REVIEW

•

VARIATION The population of the Earth is more than 6 billion people, and no two individuals (apart from identical twins) are genetically the same. Why?• People are different because they ____________________ ____________________

____________________ (or ____________________) from their parents.• Children carry a ____________________ set of ____________________; half from their

mother and half from their father.• A person’s unique characteristics are caused by:

− the ________________________________________ they inherited from their parents (____________________)

− the ________________________________________ in which they developed (____________________)

• Some characteristics, such as ____________________ colour and ____________________ shape, are only determined by genes. These are called ____________________ characteristics.

• Other types of characteristics, such as ____________________ and hair length, are not inherited but depend on ____________________ ____________________. These are called ____________________ characteristics.

• Differences in some characteristics are due to a ____________________ of both inherited and environmental factors. In some cases, it can be difficult to say how much influence each factor has.

• The overall appearance of an organism depends on:1. its ____________________ (inherited characteristics)2. the effects of the ____________________ in which it lives.

• All the observable characteristics of an organism are called its ____________________.• The full set of genes of an organism is called its ____________________.• An organism’s phenotype therefore depends on its ____________________ plus

____________________ ____________________.

VARIATION • ____________________ ____________________ is the most important cause of

____________________ ____________________ because it mixes up genetic material. • During ____________________, homologous chromosomes ____________________

genetic material. They then line up and separate in different ways, producing a large ____________________ of different ____________________.

• At ____________________, any male gamete can combine with any female gamete.

• All these events occur ____________________ and create new ____________________ of genetic material.

• ____________________ is the ____________________ in the ____________________ or ____________________ of ____________________ and is therefore another cause of genetic variation.

• Mutations can arise ____________________; for example, through the incorrect copying of base pairs during DNA replication, or the ____________________ distribution of chromosomes during ____________________ ____________________.

• Mutations can also be caused by ____________________ ____________________, such as radiation and certain chemicals. These factors are called ____________________.

• Some mutations may be beneficial, but many are harmful and increase the risk of diseases such as ____________________.

GENES & ALLELES • The basic ____________________ of ____________________ is the ____________________.• A gene is a segment of a ____________________ that contains the ____________________

required to produce a ____________________.• There are ____________________ of each chromosome , known as a ____________________

____________________. Each copy has its own ____________________ of the gene. • These versions are known as ____________________.• Most genes are controlled by ____________________.

• Dominant alleles:− ____________________ expressed in a cell’s ____________________− only ____________________ of the dominant allele needs to be inherited in order for

it to be expressed− represented by an ____________________ case letter (eg. _______)

• Recessive alleles:− only expressed in a cell’s phenotype if ____________________ are present− if only one copy is present, its effect is ‘____________________ by the

____________________ ____________________− represented by a ____________________ case letter (eg. _______)

• If the alleles for a characteristic in a homologous pair are the ____________________, the organism is said to be ____________________ for that characteristic.

• If there are ____________________ alleles, the organism is said to be ____________________ ____________________ for that gene.

• If there are ____________________ alleles, the organism is said to be ____________________ ____________________ for that gene.

GENES & ALLELES • If the alleles for a characteristic in a homologous pair

are ____________________, the organism is said to be ____________________ for that characteristic.

• The characteristic ____________________ by heterozygous alleles will depend on which allele is ____________________ and which allele is ____________________.

• The allele for brown eyes is ____________________over the allele for blue eyes. • The individual will have ____________________eyes, because the allele for brown eyes

____________________the allele for blue eyes.

TYPES OF INHERITANCE

COMPLETE DOMINANCE: ß NORMAL!!!!! • If the ____________________ allele is present, it will be ____________________• eg. Brown eyed allele (B) always expressed when present (BB or Bb) • Special symbols:

− Choose ____________________− Use ____________________ (recessive) and ____________________ (dominant)− eg. BB, bb or Bb ß _______________________________________________________

CO-DOMINANCE: • There is ________________________________________!• The phenotype is a ____________________ of both alleles present• eg. red allele + white allele = ____________________ phenotype• eg. ____________________ blood from combination of A and B alleles• Special symbols:

− Choose ____________________− Use ____________________ for both − eg. RR, WW or RW ß _____________________________________________________

ABO BLOOD GROUPING • To determine your blood type, there are three alleles:

− A –____________________− B -____________________ − O - ____________________

• The alleles IA and IB are ____________________• However, both of these alleles are ________________________________________ over ί • This results in ____________________different phenotypes.

Phenotypeor blood group

Genotypes

Type A

Type B

Type AB

Type O

TYPES OF INHERITANCE

AUTOSOMAL INHERITANCE: ß NORMAL!!!!! • The gene in question is located on an ____________________• Traits can be:

− ____________________ ____________________ – meaning that a trait/disorder is determined by the presence of a dominant allele

− ____________________ ____________________ – determined by the presence of two recessive alleles

• Special symbols:− BB, bb, Bb

SEX-LINKED INHERITANCE: • The gene in question is located on a ________________________________________• Will generally be on the ____________________, as the Y carries very few genes• eg. ____________________, ________________________________________• Traits can be:

− ____________________ ____________________ – meaning that a trait/disorder is determined by the presence of the dominant allele on the X chromosomes

− ____________________ ____________________ – meaning that a trait/disorder is determined by the presence of one or two recessive alleles on the X chromosomes

• Special symbols:− Females:

• Homozygous __________ __________ • Heterozygous __________

− Males (only one X chromosome):• Unaffected __________ • Affected __________

CARRIERS: • Someone who is ____________________ for a genetic

disorder• They ____________________ the disorder themselves• However, the disorder can be ____________________

to the next generation

GENETIC MUTATIONS

• Genes are nearly always passed from parent to offspring _____________________________.

• Occasionally a _________________ will occur in a gene.

• This is called a _________________ _________________.

• _________________ _________________:

– one base is _________________ for another

• _________________ _________________:

– _________________

• insertion of one or more bases

– _________________

• deletion of one or more bases

• • Why?

– Mutation involves a part of the DNA which that particular cell ____________________– Mutation occurs but the code

still results in the same __________________________________ & therefore the same _________________

• Generally, _________________ mutations are more serious.

PUNNETT SQUARES • Also called _________________ _________________• Method used to find the _________________ genotype and phenotype ratios of

_________________ when the parental genotypes and/or phenotypes are known.

• Steps: 1. Write down the _________________ _________________

You may need to choose letter to represent your trait – choose easy ones like T, G, H not C, S, Y

2. Write down the _________________ _________________ that they are able to pass on in their gametes (sex cells)

3. Construct the Punnett square4. Fill in the _________________ _________________ of the offspring 5. Determine the _________________ _________________ of the offspring6. Determine the _________________ _________________ of the offspring

PUNNETT SQUARES

• Example:

An alien that is homozygous dominant for green skin has chosen an alien who has purple skin for his bride. Determine the likelihood that their children will have purple skin.

Like in Maths – you need to state what symbols you will be using to represent your traits:

eg. Let G = green; g = purple

• Example: One of the couples sons (Neyp) married a female alien who was homozygous recessive for the skin colour trait. Work out the genotype and phenotype percentage of their potential offspring.

PUNNETT SQUARES

• Example:

One of Neyp’s sons married a female alien who was homozygous for haemophilia.

Calculate the likelihood that they could have a child with haemophilia.

Again – specify your symbols!

It is a sex-linked recessive disorder!!!

So: Let H = _________________; h = _________________

PEDIGREE CHARTS • Shows the members of a family and how they are _________________ to each other.• A ___________________________________________________!

• Pedigree charts can also be used to _________________ the _________________ of a _________________.

• Circles = _________________

• Squares = _________________

• Shading = _________________ individuals

• Parents = linked by a _________________ line

• Children = _________________ lines running down from parents

• Siblings = linked by a _________________ line _________________ them

PEDIGREE CHARTS

• Example: Draw a pedigree chart for Neyp and his wife Gjup., including their parents and children. They had 3 children, 2 boys and a girl. Their daughter Hefg had purple skin and married an alien who also had purple skin. They had one son – Yerg. Their son Guol had green skin and was also married with one purple daughter, Zcug.

Remember, being purple is the recessive trait!

• Pedigree charts can also be used to determine if:

– The characteristic is _________________ or _________________.

– The characteristic is _________________ or _________________.

• Things to look for:

– Gender bias of males:females

– Affected offspring from unaffected parents

– Affected sons from affected fathers

PEDIGREE – A FAMILY TREEMake your own family tree for one trait of your choosing (eye colour, natural hair colour, or blood type).

Include as many people on your immediate family as possible and use all of the rules for pedigrees. Identify the names and genotypes of all individuals in your pedigree.

Attach answers to textbook Qs to the back of the booklet