Genetics


	Genetics Notes

Question: What is Biology?

A. Biology- study of life. (bio)

1. life- we cannot define but we can describe the characteristics.

�� a. Cell

�� b. Nutrition

�� c. Reproduction

�� d. Regulation

�� e. Growth

�� f. Excretion

�� g. Transportation

h. Respiration- Breathe. They breathe oxygen in and Carbon Dioxide out. This is called gas exchange. Why do we need this? We need to releases energy from the food. The energy we are releasing is food. However plants are taking in Carbon Dioxide and exhaling oxygen. This is called Photosynthesis.

Question: What is Genetics? Genes, chromosomes, DNA.

A. Genetics- study of heredity. Heredity is traits that you inherit from one generation. In some situations there are not two parents. The exact definition of Heredity is the transmission of traits from one generation to another/the next.

- Before Mendel, people had different hypotheses.

1. Mendel�s experiments- Gregor Mendel was an Austrian monk who studied traits of people plants for over 7 years. He proved the blending hypothesis wrong. Mendel was called the �Father of Genetics.�

�� a. Why did Mendel test Peas Plants?

�� 1. Short generation span

�� 2. Easily distinguishable traits

3. He chose an organism that self-fertilizes. He chose an organism that can cross and self- fertilize.

4. He chose an organism that has a large number of offspring.

5. He chose an organism that is easy to grow.

- Pea plants was a very good choice.

2. Pea plant genetics- It is from the pea plants that we learn about organisms.
�� a. Allele- alternative forms of a gene.

�� e.g. seed color in peas- yellow or green

Mendel said he wanted to have an organism that was what he thought it was.

b. True breeding- pure breeding plants. With respect to seed color, always produce yellow seeds if that plant was a yellow true breeding plant. And if they always produce green seeds, they are true breeding green.

c. P (Parental)- Yellow (true breeding) x� Green (true breeding)

�� ↓

F1- First Filial Generation-Yellow- they were 100% yellow. He looked at more than 1000 offspring. The genotype was Yy. It has to be Yy because it�s from YY and yy. In pea plants, yellow is dominant to green. Yellow is Y. Green is y. If it�s pure breeding for yellow, it must be YY. If it�s pure breeding for green, it would be yy. Mendel didn�t know that the offspring were going to be 100% yellow. The only way for him to know was for him to experiment. Now Mendel took the F1�s and self crossed them.

�� ↓

�� F2- Second Filial Generation- 3 yellow : 1 green.

d. Mendel came up with the Law of Dominance- When you have two alleles for a given trait present, the one that is seen is dominant.

e. Recessive- the trait that is masked or hidden or does not show up.

f. Convention of Lettering- Biology has given letters to things. Dominant- yellow- Capital letter- Y. Recessive- green- lower case- y. When you deal with many traits, it gets confusing if you use different letters for dominant and recessive. It is much easier to understand if you use the same letter for the same trait.

g. Gametes- sex cells- sperm cells and egg cells. In plants we might say sperm is pollen. Every single one of us was made from egg and sperm. When they form, now there are two copies of the gene for each trait. In each gamete, there is 1 copy of a gene for each trait. [Every cell in the body formed from the sperm and the egg will have to copies of the genes for each trait.]

�� Yy x Yy

�� yy, Yy, Yy, YY

h. Punnett Square- Mendel wanted to find a better way to find out results of that cross.

��

�� y

i. �Genotype- actual genetic makeup- YY (pure breeding), Yy, yy.

j. Phenotype- the appearance- what you see- Possible phenotypes are yellow or green.

k. Homozygous- Homo means same. Homozygous is similar to pure breeding. Homozygous is 2 same alleles. In terms of seeds, 2 possibilities are YY or yy. In the formation of gametes, one will have Y and one will have y.

l. Heterozygous- Hetero means different. Another word for heterozygous is a hybrid. Heterozygous is 2 different alleles- Yy.

m. When Mendel tested YY with yy, he didn�t know what happened to the green. However, when he self-fertilized the F1, the green came back. Mendel came up with a Law of Segregation- the two alleles separate during the formation of gametes and then they recombine during the combination with Y and y. By chance, the y and another y combined and then the green reappeared. The Law of Segregation- genes that occur in pairs, before gametes are formed, separated from each other during gamete (sex cell) formation and then they can recombine at fertilization.

What is a testcross?

A. You cross the unknown with a recessive yy. It is a yellow seed with an unknown genotype. There are two possibilities: YY or Yy. YY x yy or Yy x yy. If you do cross the first possibility 100% will be yellow. However, the second possibility would make 50% yellow and 50% green. If you would cross Yy x Yy, 25% would be green. That�s why we use that as a testcross.

What is independent assortment?

Independent Assortment

1. When Mendel did his experiment he looked at one trait at a time. Now he said that he should look at something different. He looked at 7 different traits.

�� a. He looked at tall and short. Tall is dominant so tall is T and short is t.

P= TT x tt

F1= 100% were tall with TT genotype.

F2= TT, Tt, Tt, tt.

�� 3 tall: 1 short

b. Then Mendel said that he would take tall yellows and cross them with short green.

�� P= TTYY�� X�� ttyy

�� F1= TtYy

�� 100 percent were tall yellow.

��

TtYy

c. Now Mendel wanted to cross the F1 generation.

TtYy� x TtYy. He had to cross two hybrids which is called a dihybrid cross.- he did a dihybrid cross of tall yellows and short greens.

- TtYy- what are the possible gametes?

�� 1. TY, Ty, tY, ty

TTYY

TTYy

TtYY

TtYy

TTYy

TTyy

TtYy

Ttyy

TtYY

TtYy

ttYY

ttYy

TtYy

Ttyy

ttYy

ttyy

- In the table above, it shows Mendel�s results in the F2 generation. The results were:

A. 9 Tall Yellow- To see in the table which results were tall yellow, the result has to be Y or anything and T and anything.

B. 1 short green- to see in the table which results were short green, the result has to be ttyy.

- Both A and B are parental types.

C. 3 tall greens- to see in the table which results were tall green, the result has to be T or anything and yy.

D. 3 short yellow- to see in the table which results were short yellow, the result has to be Y or anything and tt.

- Both C and D are called recombinants because they didn�t exist before they were crossed and then they recombined.

- Independent Assortment- genes for different traits are separated and distributed to gametes independently of each other.

What is intermediate inheritance?

A. Intermediate Inheritance

1. Four o� clock plants- plants that are very sensitive to light. �closes at four o� clock.� These plants respond to the light. They come in various colors/varieties.

P= Red (RR) x White (WW)

↓

F1 Pink (self-crossed)

↓

F2: 1 red: 2 pink: 1 white

We have to designate the colors with letters. Red= R and White= W (R�). Both are capital letters because both of them are dominant- co dominance- no lower case letters. ��

The offspring- F1 generation is 100% pink.��

Pink= RW.

Now the F1 generation is self crossed

RW x RW

��

Ratio is 1 red: 2 pink: 1 white= 1:2:1

- Roan cattle- they come in white and red and when they mate they will be spotted white and red fur.

-What are multiple alleles?

�� A. Multiple Alleles

�� 1. When more than two alleles exist for a particular trait.

a. Human blood groups- A, B, AB, O- looking at these letters, we see that AB has both A and B. This is an example of co dominance.

�

Blood Types�� Red Blood Cell�� Genotypes

A	The red blood cell is surrounded by A carbohydrates.	IAIA, IAi.
B	The red blood cell is surrounded by B carbohydrates.	IBIB, IBi
AB	The red blood cell is surrounded by both A and B carbohydrates.	IAIB
O	The red blood cell is not surrounded by any carbohydrates.	ii

- These four blood types are the four major blood groups.

- Allele for A is written like IA

- Allele for B is written like IB

- Allele for O is written like i.

If a child has O blood type, the parents don�t have to have O. One parent could have type IAi and another parent could have type IBi.

IAi x IBi= O.- this is often used for paternity cases.

If a mother is type A and the father is type O it is impossible for the baby to have type AB blood.

- If two guys are claiming paternity and the Mother is type B and Father 1 is type AB and Father 2 is type O and the baby is type AB, Father 2 is not the father because O is recessive.

***(For some reason, Doctor Fruchter went to a different topic for a few minutes and this is what I took notes about for those few minutes.)

Guinea Pigs- black is dominant to white. If a heterozygous black is crossed with a pure breeding white, half will be black and half will be white.

��

- (Now continuing from with baby�s blood type is O)

- Mendel tested 7 traits. If he would have tested one more, it would not have worked out. Now all genes independently assorted. So, when he got to the 8^th trait, it probably did not work so he left it alone. Maybe this is why he only tested 7 traits.

What are linked genes?

A. Linked genes- genes located on the same chromosome and are usually inherited together. In our body we have 46 chromosomes. 23 from our mother and 23 from our father.

1. If there is a double stranded chromosome, there will be another double stranded chromosome from the opposite parent. If, on one chromosome there is height, on the other part of the double stranded chromosome there will be height. Also, height on the other chromosome will be in the same exact place as height is on the other chromosome. Each trait will be in the same position on the chromosomes. Examples in Humans:

a. Blonde hair and blue eyes come together.

b. Red hair and freckles come together.

B. Linked genes may be separated by crossing over- when two linked genes tangle and then separate. For example, if the chromosome that has blonde hair and blue eyes on it crosses over with the chromosome that has brown hair and brown eyes, the offspring might get blonde hair and brown eyes or brown hair and blue eyes.

How is sex determined?

How come we are male or female? We have 46 chromosomes.

A. Sex determination

1. Humans have 46 chromosomes- 23 pairs of chromosomes. 2 chromosomes= 1 pair.

B. Sex Chromosomes

1. Males- combination is xy

2. Females- combination is xx.

- How did we name the combinations? When we look under a microscope, for a female, it looks like an x and the x chromosome is bigger than the y chromosome. For a male, the x is so small that it looks like a y. How is there a 50/50 chance for a girl and a boy?

50% are male and 50% are female. It turns out that slightly more males are conceived because the y chromosome moves faster because the y chromosome is smaller.

What are sex-linked traits?

-Colorblindness is only found in males- Why?

�� A. Sex Chromosomes

1. x chromosome is larger and carries more genetic information than the y chromosome. Sex linked traits are more common in males. Human examples: Colorblindness and hemophilia-not able to clot blood properly. These are the most common sex linked traits.

- H= normal condition

- h= allele for hemophilia.

xHxh-carrier (hybrid)� x�� xHy- not carrying information about the trait.

��

xHxH

xHy

xHxh

xhy

�

- Out of the F1 offspring, 1 male will get the condition. The females will not have the condition. One will be a carrier and one male will not have the condition.

- Of the offspring, 1 is a carrier.

- 50% of the male offspring are normal.

- 75% of the offspring are normal.

- 25% of the offspring is male and normal.

- Males either have the condition of do not. They cannot be carriers.

- xHxh� x� xhy

��

xHxh

xhxh

xHy

xhy

- xHxH� x� xhy

��

xHxh

xHy

xHxh

xHy

��

- 0% of the offspring in this cross have the disease.

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