Ch. 11 Notes - Genetics

Ch. 11 Notes - Genetics

A. Gregor Mendel - Austrian monk who studied how traits are inherited; known as the “Father of Genetics”

1. Genetics - branch of biology that studies heredity

a. Heredity - passing on of traits from parent to offspring

I. Who was Gregor Mendel?

B. Mendel’s Experiments1. Studied/Researched on pea plants

a. They have many traits such as flower color (purple or white), peas (round or wrinkled), pea color (yellow or green) and height (tall or short).


b. Mendel bred a tall pea plant with a short plant (P generation).

c. The offspring in the 1st generation (F1

generation) were all tall.


Short pea plant Tall pea plant

All tall pea plants

3 tall: 1 short

P1

F1

F2

d. Then, he bred two of the F1 plants.

e. The offspring in the 2nd generation (F2 generation) were 75% tall and 25% short.

f. The short trait disappeared in the 1st generation and reappeared in the 2nd generation.


Short pea plant

Tall pea plant

All tall pea plants

3 tall: 1 short

P1

F1

F2

2. Mendel discovered that each trait is controlled by alleles. a. Alleles: forms/versions of the same gene

Each person has TWO alleles for each gene; 1 from mother and 1 from father.

Ex: T = the allele for tall; t = the allele for short


Short pea plant

Tall pea plant

All tall pea plants

3 tall: 1 short

P1

F1

F2

◦Some alleles are dominant and recessive Dominant - a trait that is always expressed

(seen) in an individual if the allele is present (capital letter) Ex: T = tall allele

Recessive - a trait that is hidden by the dominant allele; expressed only when two copies of the recessive allele are inherited (lowercase letter) Ex: t = short allele


◦Individuals can be described by their genotype and phenotype Genotype - genetic makeup (letters); alleles

present in an individual Ex: TT, Tt, tt

Type of Genotypes: Homozygous - two of the SAME alleles for a trait

Ex: TT or tt Heterozygous (hybrid) - two DIFFERENT alleles for a

trait Ex: Tt


◦Phenotype - physical appearance; what traits are expressed in the individual Ex: tall or short plants


TT, Tt=tall tt=short

A. Punnett Square/Test Cross - a tool used to predict the alleles/traits present in offspring

1. When parents produce gametes (sperm or eggs), their genes separate to produce

haploid cellsa. Each gamete contains ONE allele

II. Punnett Squares/Test Crosses

T T

Homozygous Tall DadHeterozygous Tall Dad

T t t t

Homozygous Short Dad

B. How to Solve a Monohybrid Cross1. Determine the genotypes (letters) of the

parents. 2. Set up the punnett square with one parent

on top and one parent on the side.3. Fill out the Punnett square boxes (Look up

and over to the left to fill them in).4. Analyze the probability (likelihood) that

the offspring would possess each specific trait.


C. PracticeY = yellow pea color; y = green pea color

1. Cross two heterozygous pea plants. Parent 1 Genotype __________ Parent 2 Genotype __________ What is the chance of the offspring having yellow pea

color?


Genotypic Ratio:

Phenotypic Ratio:

YY : Yy : yy

yellow : green

Y = yellow pea color; y = green pea color2. Cross a homozygous recessive pea plant with

a heterozygous pea plant. Parent 1 Genotype __________ Parent 2 Genotype __________ What is the chance of the offspring having yellow pea

color?


Genotypic Ratio:

Phenotypic Ratio:

YY : Yy : yy

yellow : green

Y = yellow pea color; y = green pea color3. Cross a homozygous recessive pea plant with

a homozygous dominant pea plant. Parent 1 Genotype __________ Parent 2 Genotype __________ What is the chance of the offspring having yellow pea

color?


Genotypic Ratio:

Phenotypic Ratio:

YY : Yy : yy

yellow : green

D. How to Solve a Dihybrid Cross1. Determine parent genotypes (letters).

2. Determine gamete combinations from mom and dad. (FOIL method from math class - Use arrows!)3. Write the gametes from mom on 1 side of the

square and dad on the other side.4. Fill in the boxes in the punnett square (look up and to

the left).5. Analyze the probability (likelihood) that the offspring would possess the specific traits.


PRACTICE: R = round peas, r = wrinkled peas Y = yellow pea color; y = green pea color

◦Cross two heterozygous round yellow pea plants. Parent 1 Genotype _____ Parent 2 Genotype _____

Parent Gamete Possibilities: FOIL

Parent #1 Gametes: RY, Ry, rY, ryParent #2 Gametes: RY, Ry, rY, ry


What is the chance of the offspring having round and yellow peas?

RY

RY

Ry

Ry

rY

rY

ry

ry

A. Autosomes - 22 pairs of body chromosomes in a human

III. Special Inheritance

22 Autosomes Sex chromosomes

B. Sex chromosomes - 1 pair of chromosomes in a human; the last pair in a karyotype

a. Ex. XX-female XY-male


22 Autosomes Sex chromosomes

Show a punnett square crossing male and female sex chromosomes.


d. Every time a male and female have a baby, what is the chance of them having a son? A daughter?

e. If a female has 5 sons in a row, what is the chance of her having another son? A daughter?

f. Which parent determines the sex of the child? WHY?

C. Sex-Linked Traits - traits located on the sex chromosomes (usually the X chromosome)

a. Dad gives X chromosome to daughters and Y chromosome to sonsb. Mom gives X chromosome to daughters and sons

If a male inherits a sex-linked trait, which parent(s) gave him the trait? MOM

If a female inherits a sex-linked trait, which parent(s) gave her the trait? MOM OR DAD

Who (males or females) is most likely to inherit a sex-linked trait? WHY? Males – they only need to inherit ONE X chromosome


c. Examples in humans Male pattern baldness Red/green colorblindness Hemophilia (problems with blood clotting) Muscular Dystrophy (muscle weakness, loss of

muscle tissue)


d. Other Examples Eye color in Drosophila (fruit flies)

R = Red eye Color; r = white eye color

Cross white eyed male (XrY) with red eyed female (XRXR)


What percentage of offspring are likely to have red eyes?

What percentage of female offspring are likely to have red eyes?

What percentage of male offspring are likely to have red eyes?

◦ Examples Eye color in Drosophila (fruit flies)

R = Red eye Color; r = white eye color

Cross white eyed male (XrY) & heterozygous red eyed female (XRXr)


What percentage of offspring are likely to have red eyes?

What percentage of female offspring are likely to have red eyes?

What percentage of male offspring are likely to have red eyes?

A. Incomplete Dominance - heterozygous individuals display an intermediate (blending) phenotype of the two homozygous individuals

1. Examples in humans Hair texture

SS = straight CC = curly SC = wavy

Tay Sachs Disease (inability to produce enzyme that breaks down lipids)

EE = produces enzyme NN = does not produce enzyme EN = produces half amount of enzyme

IV. Not all traits are controlled by simple dominant and recessive alleles!

2. Other Examples Flower color in snapdragons

RR = Red, WW = white, RW = pink Cross a red flower with a white flower. Parent 1 Genotype ______ Parent 2 Genotype _____ What is the chance of producing a pink flower?

IV. Not all traits are controlled by simpledominant and recessive alleles!

Phenotypic Ratio: red: pink: white

Genotypic Ratio: RR : RW : WW

Cross a pink flower with a pink flower. Parent 1 Genotype _____ Parent 2 Genotype _____ What is the chance of producing a white flower?

III. Not all traits are controlled by simple dominant and recessive alleles!

Phenotypic Ratio: red: pink: white

Genotypic Ratio: RR : RW : WW

B. Co-dominance - heterozygous individuals display BOTH traits of the two homozygous individuals

1. Examples in humans Sickle Cell Anemia (abnormally shaped red blood cells)

NN = normal shaped cells SS = sickle shaped cells NS = normal and sickled shaped cells

Blood Type Type A Type B Type AB

III. Not all traits are controlled by simple dominant and recessive alleles!

***** Special Inheritance *****◦ Hemoglobin—protein that carries oxygen in blood,

makes blood red In homozygous recessive individuals—hemoglobin is

defective and makes blood cells sickle (half moon) shaped These blood cells—cause slow blood flow, block small

vessels, tissue damage and pain In heterozygous individuals – both normal and sickled

hemoglobin are produced They produce enough normal hemoglobin that they do not

have serious health problems

2. Other Examples Coat color in chickens

BB = black WW = white BW = black AND white speckled

Cross a black rooster with a white chicken. Parent 1 Genotype _____ Parent 2 Genotype _____ What is the chance of producing black and white chicks?


Phenotypic Ratio: black: black/white: white

Genotypic Ratio: BB: BW : WW


Complete the last cross on your own. Be ready to discuss.

A. An example of multiple alleles – more than one allele controls the traitB. It is determined by the presence or absence of proteins (chains of amino acids) on the surface of red blood cells

a. Mixing incompatible blood types can cause blood clots, which can result in death

V. Blood Type (codominance in humans)

Human Blood Types


Phenotype

Genotype Blood cell surface molecules (antigens)

Type A IAIA or IAi A antigensType B IBIB or IBi B antigensType AB IAIB A and B antigens

Type O ii No antigens


V. Blood Type (codominance in humans)C. Alleles IA and IB – are co-dominant to each other

D. Allele i –is recessive to both IA and IBa. Type O blood — universal donor Has no proteins on the blood cells so any blood type can

receive it

b. Type AB blood — universal acceptor

Has both proteins on blood cells so this blood type can receive any blood

E. Cross parent with A ( IAi) blood with a parent with B blood (IBi).


IA i

IB

i

IAIB IBi

IAi ii

Genotypic ratio0 IA IA : 1 IA i : 0 IB IB :1 IB i : 1 IA IB : 1 ii

Phenotypic ratio (blood type)—1 type AB : 1 type A : 1 type B : 1 type O

A. Rh Positive = have proteinsa. Genotypes: Rh+/Rh+ or Rh+/Rh-

B. Rh Negative = no proteinsb. Genotype: Rh-/Rh-

VI. Rh Factor – describe the presence or absence of another protein on blood cells.

C. Cross parent heterozygous for the Rh factor with another parent who does not have the Rh factor.

Rh+ Rh-

Rh-

Rh-

Rh+/Rh- Rh-/Rh-

Genotypic ratio0 Rh+/Rh+ : 2 Rh+/Rh-: 2 Rh-/Rh-

Rh+/Rh-Rh-/Rh-

Phenotypic ratio2 Rh positive: 2 Rh negative

VI. Rh Factor – describe the presence or absence of another protein on blood cells.

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Ch. 11 Notes - Genetics