Biology 30 – Unit 3

~Mrs. S. Pipke-Painchaud

What is Genetics?

• -a branch of biology that deals with the heredity of an organism

• It is a field in which every year large numbers of significant findings are made. Over the past 5 decades, no five year period has passed without the establishment of 1 or more major research frontiers in genetics.

• Genetics is a science, which surrounds us and determines our everyday lives.

• Just look at the person next to you (everyone is unique and different because of their genes)

• It is not known when people first recognized the existence of heredity; however, archeologists have discovered evidence (primitive art, preserved bones, skulls and dried seeds), which suggests that animals were domesticated and plants were cultivated thousands of years ago.

Selection of Animals

• Between 8000 and 10 000 B.C. horses, camels, oxen and various breeds of dogs (dogs are derived from the wolf family) were domesticated to serve various roles.

• Evolution Homepage. http://www.nwcreation.net/dogsandwolves.html

• Likely domesticated in China about 15 000 years ago. (Ev Homepage)

• For example, horses– Arabian horses: this breed was

developed in the deserts of the Middle East by the nomadic tribes that lived there.

– Eventually, the desert breed developed into 4 different strains. (i.e Polish, Spanish, Egyptian, Russian)

– many horse breeders keep detailed pedigrees, which show the ancestors of the animal that they own.

• Pedigrees are similar to family trees

• in Roman times they grafted plants and bred animals to obtain desired traits or characteristics.

• Eventually, Darwin and Mendel began to develop the theories of genetics which is where we will start our study of genetics

Why is Genetics important to society?

• Agriculture (genetically engineered plants, wheat resistant to rust)

• Livestock (different breeds, leaner beef, polled vs. horned cattle)

• Medicine (to discover the cancer causing gene, diagnose a disease, gene therapy, genetic screening, etc.)

Gregor Johann MedelThe Father of Genetics

• 1822-1884• Austrian Monk• born to a peasant family in Heinzendorf (Czech Republic) – July 22, 1822• Was considered an excellent student in high

school• Then he studied philosophy for several years• In 1843, he was admitted to the Augustinian

Monastery of St.Thomas in Brno• Here he took the name of Gregor and received

important support for his studies and research

Pictures & more info available from: (Zephyrus http://www.zephyrus.co.uk/gregormendel.html)

• The Austrian Monastery • Wikipedia.• http://en.wikipedia.org/wiki/Image:StThomasAbbeyBrno.jpg

• In 1849, he was relived of his pastoral duties and accepted a teaching appointment

• From 1851 – 1853, he attended the University of Vienna to study physics and botany

• He was sent to the University of Vienna for a teaching certificate. He did not pass the exams because he was too nervous and was not considered a clever student. (Zephyrus)

• In 1854, he returned to Brno where he performed his first pea hybridization experiment in 1856

• He continued to research until 1864 when he became the abbot of the monastery.

• Some did not appreciate the work that Mendel was doing because he did not focus completely on the religious side. Mendel was interested in the work of Charles Darwin. (Zephyrus)

• In 1884, he died of kidney disease• The new abbot burned his papers.

(Zephyrus)

Mendel Web: http://www.mendelweb.org/images/lathyrus.mar.GIF

• The local newspaper said this: “His death deprives the poor of a benefactor, and mankind at large of a man of the nobliest character, one who was a warm friend, a promoter of the natural sciences and an exemplary priest.”

• Mendel’s work was not understood or appreciated while he was alive and it wasn’t until the 1900s and even into the 1920s and 30s when people truly understood what he had discovered. (Zephyrus)

Mendel’s Experiments

• conducted experiments with pisum sativum – the garden pea

• he wasn’t the first scientist to study the garden pea, but he was one who distinguished himself from others through 1) careful planning and 2) adherence to the scientific method

• his work, however, was largely ignored by others until Correns, de Vries, Tschenmak and Bateson all came up with the same ideas.

Mendel Selected the Garden Pea because . . .

1. it was cheap and readily available as seed in a variety of shapes and colors.

2. Normally self pollinates3. It’s easy to cross pollinate4. Takes up little space5. Have relatively short generation time

(single season)6. Produces many offspring (1 pod = 6-10

peas)

Consider the time . . .

• Remember that when Mendel was conducting these experiments there was no knowledge of chromosomes or the role and mechanisms of meiosis.

• Regardless, Mendel was still able to find distinct units of inheritance existed and then he used this information to predict the behavior of gametes during their formation.

Selected Characteristics

1. flower color: purple or white

2. flower position: axil or terminal

3. stem length: tall or dwarf

4. pod shape: inflated or constricted

5. seed shape: round or wrinkled

6. seed color: yellow or green

7. pod color: yellow or green

** notice that each unit has a contrasting characteristic

** all strains used were “true breeding” peas seeds– offspring looks like the parent i.e. white

flowers give rise to white flowers– each trait (characteristic) remains unchanged

generation after generation.

** TRAIT: is a characteristic that is heritable from one generation to the next.

• http://fig.cox.miami.edu/~cmallery/150/mendel/c7.14.1.traits.jpg

• Science Quarterly. http://www.scq.ubc.ca/a-monks-flourishing-garden-the-basics-of-molecular-biology-explained/

Mendel’s Experiments were successful because. . .

1. he choose peas2. he restricted his study to

a few contrasting traits3. he kept accurate quantitative

records4. his analysis of the data

allowed for certain postulates to be developed which provided the underlying basis for transmission genetics

The Experiment

• 1ST: Cross true breeding pea plants that had different characteristics with each other.

• 2nd: he would examine the peas and record the results

• 3rd: he would collect the seeds that were the result of the cross and then plant these seeds and then collect data on them

Example: Round/Wrinkled

• 1st: Parent 1 (Round) X Parent 2 (wrinkled)

• 2nd: First Filial Generation = F1

• 3rd: F1 X F1

• = F2 or second filial generation

http://www.mendelu.cz/images/mendel_krizeni2.png

Monohybrid Cross

• Monohybrid Cross: consider only one trait

Round X Wrinkled

F1 = all round seeds

so the next season Mendel planted 253 F1 plants

F1 X F1 = F2 produced 7 324 seeds

5 474 Round

1 850 Wrinkled

http://fig.cox.miami.edu/~cmallery/150/mendel/sf10x4.jpg

Terminology

• Dominant: when one characteristic expresses itself over the other i.e. round over wrinkled

• Recessive: the trait that does not show through in the first generation i.e. wrinkled

The Experiment cont’d

• he repeated these experiments for all of the other characteristics and in each case a 3:1 ratio appeared

• 3 dominant : 1 recessive

Mendel’s Laws of Heredity

The Law of Unit Factors in Pairs• Genetic characters are controlled by unit factors that

exist in pairs in individual organisms.• unit factors are genes.• Ex.. a monohybrid cross for round and wrinkled

provides three combinations• 2 factors for round• 1 factor round 1 factor wrinkled• 2 factors for wrinkled• every individual must have one of these three combos

The Law of Dominance• When 2 unlike unit factors are responsible for

a single character and are present in a single individual, one unit factor is dominant to the other, which is said to be recessive.

Ex.. look at monohybrid crosses and the f1 generation

– One gene pair may mask or prevent the expression of the other.

The Law of Segregation

• During the formation of gametes, the paired unit factors separate from each other sot that each gamete receives one or the other.

– Ex.. think back to what happens in meiosis

http://www.animalgenome.org/edu/genetics/meiosis.gif

Mendel’s Reasoning

1. p1 plants that were true-breeding round had 2 unit factors for round

2. p2 plants also had two unit factors for wrinkled3. gametes of the parents each received one unit factor4. after fertilization all f1 plants had 1 unit factor from

round and 1 from wrinkled5. when the f2 gametes are formed there are 4 possible

random outcomes6. r/r; r/w; w/w; w/r7. according to the law of dominance 1 and 4 will be

round as well8. Therefore, you get a three to one ratio

Genetic Terminology

• Gene: Mendel’s unit factor; found at a specific point on the chromosome; carries the information for a specific trait

• Ex// seed shape

http://www.ndsu.edu/instruct/mcclean/plsc431/mendel/peashape.gif

Genetic Terminology

• Phenotype: the physical appearance of a trait

Ex// if the plant is tall or short; seed color yellow or green

• Genotype: the letters assigned to that trait

Ex// Aa

http://www.visionlearning.com/library/modules/mid129/Image/VLObject-3225-050214020235.jpg

Genetic Terminology

• Allele: is an alternate form of a single gene

Ex// the unit factors round and wrinkled are alleles that make up seed shape.

Hints for working with genetic traits . . .

• traits are assigned letters• the recessive trait usually provides the letter designate

Ex// round vs. wrinkled = W= round w= wrinkled• (be sure to keep your writing neat enough so that you

can read the letters)• Capital letters refer to dominant traits while lower case

letters refer to recessive traits• Letters usually appear in pairs

• Ex// Round = WW vs Wrinkled = ww

• remember the genotype will tell you the phenotype.

Genetic Terminology

• Homozygous: both alleles are the same – Ex// WW or ww

• HOMO = SAME

• Heterozygous: when alleles are different– Ex// Ww

• HETERO = DIFFERENT

Punnett Squares

• named after Reginald C. Punnett

• a way of visualizing various crosses

• aids in problem solving

• the square represents all possible random fertilization events.

So if you cross round by wrinkled WW X ww

W W w Ww Ww w Ww Ww

Genotypic ratio—all Ww Phenotypic ratio – all round

F1 X F1

W w W WW Ww w Ww ww

Genotypic ratio = 1 WW: 2 Ww: 1ww

Phenotypic ratio = 3 round : 1 wrinkled

Types of Monohybrid Crosses

1. Pure Cross: true breeding X true breeding

WW X ww

2. Hybrid Cross: F1 generation X F1 generation

Ww X Ww

3) Test Cross:

~ a cross between an individual of unknown genotype with one individual that is homozygous recessive.

W W

w Ww Ww

w Ww Ww

If all the same the unknown individual must be homozygous dominant. (WW)

Test Cross . . .

W w

w Ww ww

w Ww ww

If you get a 1:1 ratio the unknown individual must be heterozygous dominant.

Try these:

• Try the following question:

• In people, freckles is dominant trait. If you cross a person homozygous for freckles with a person homozygous for no freckles. What will the offspring look like (phenotype)?– N = Freckles– n = no freckles– NN X nn

N N

n

n

N N

n Nn Nn

n Nn Nn

G: All would be NnP: All would have Freckles.

Part B:

• If you crossed an individual from the F1 generation with a person heterozygous for freckles, what would the genotypic and phenotypic ratios be?– N – Freckles– n – no freckles– Nn X Nn

N n

N

n

N n

N NN Nn

n Nn nn

Genotype: 1 NN: 2 Nn: 1 nn

Phenotype: 3 Freckles : 1 Non freckle

Now Try

• Next try the assigned questions in the Bio 30 duotang:– Monohybrid Crosses

Resource Websites:

• Science of Heredity. http://fig.cox.miami.edu/~cmallery/150/mendel/heredity.htm