11-3 EXPLORING MENDELIAN

GENETICS

1. Independent Assortment

Independent Assortment- Genes that segregate (separately) independently do not influence each other's inheritance.

The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.

Mendel did a two-factor (trait) cross to see if the separation of one pair of alleles affects the separation of another pair of alleles.Instead of crossing a yellow seed with a green

seed; he observed seed color and seed shape together

Seeds that are round (R) and yellow (Y) are dominant to seeds that are wrinkled (r) & green (y)

True-breeding round & yellow (RRYY)seeds were crossed with true breeding wrinkled and green seeds (rryy)

The result: All individuals in the F1 generation were round & yellow

The Two Factor Cross: F2

Heterozygous F1 plants (RrYy) were crossed with each other to determine if the alleles would segregate from each other in the F2 generation.

RrYy × RrYy

The Punnett square predicts a 9 : 3 : 3 :1 ratio in the F2 generation

9 round & yellow: 3 round & green: 3 wrinkled & yellow: 1 wrinkled & green

The results of the experiment:some seeds were round and yellowsome seeds were wrinkled and greensome seeds were round and greensome seeds were wrinkled and yellow

Mendel had discovered the principle of independent assortment

Independent Assortment explains the variation observed in plants, animals, and other organisms

A Summary of Mendel's Principles

Genes are passed from parents to their offspring.

If there are two or more alleles for a gene, some of the alleles may be dominant and others may be recessive.

In most sexually reproducing organisms, each adult has two copies of each gene. These genes are segregated from each other when gametes are formed.

The alleles for different genes usually segregate independently of one another

2. Beyond Dominant & Recessive Alleles

Not all traits or dominant or recessive

Some traits are controlled by more than one gene or many alleles

Incomplete Dominance-

One allele is not completely dominant over the other

The heterozygous phenotype is b/w the two homozygous phenotypes

A cross between red (RR) and white (WW) four o’clock plants produces pink-colored flowers (RW).

Codominance-

both alleles contribute to the phenotype.

Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately.

Multiple Alleles-

Genes that are controlled by more than two alleles

more than two possible alleles can exist in a population

Coat color in rabbits is determined by a single

gene that has at least four different alleles.

C = full color; dominant to all other alleles

cch = chinchilla; partial defect in pigmentation; dominant to ch and c alleles

ch = Himalayan; color in certain parts of the body; dominant to c allele

c = albino; no color; recessive to all other alleles

Polygenic Traits-

Traits controlled by two or more genes

Skin, hair, & eye color in humans are polygenic traits controlled by more than four different genes

3. Applying Mendel's Principles

Thomas Hunt Morgan used fruit flies to advance the study of genetics

Morgan and scientist tested Mendel’s principles and learned that they applied to other organisms as well as plants.

Mendel’s principles can be used to study inheritance of human traits and to calculate the probability of certain traits appearing in the next generation

4. Genes & the Environment

Characteristics of any organism are determined by the interaction between genes and the environment.Ex: an individual has the gene to develop

type 2 diabetes but their diet (environment) will determine if the will have it.