Chapter 11-3: Exploring Mendelian Genetics

To determine if the segregation of one pair of alleles affects the segregation of another pair of alleles, Mendel performed a two- factor cross. Independent Assortment 11-3

The Two-Factor Cross: F 1 The Two-Factor Cross: F 1 Mendel crossed true-breeding plants (genotype RRYY) with true- breeding plants (genotype rryy). Mendel crossed true-breeding plants (genotype RRYY) with true- breeding plants (genotype rryy). All of the F 1 offspring produced round yellow peas (RrYy). All of the F 1 offspring produced round yellow peas (RrYy). 11-3

The alleles for round (R) and yellow (Y) are dominant over the alleles for wrinkled (r) and green (y). 11-3

The Two-Factor Cross: F 2 The Two-Factor Cross: F 2 Mendel crossed the heterozygous F 1 plants (RrYy) with each other to determine if the alleles would segregate from each other in the F 2 generation. Mendel crossed the heterozygous F 1 plants (RrYy) with each other to determine if the alleles would segregate from each other in the F 2 generation. RrYy × RrYy 11-3

The Punnett square predicts a 9 : 3 : 3 :1 ratio in the F 2 generation. 11-3

dihybrid Phenotype ratio from dihybrid cross is 9/16:3/16:3/16:1/16 or 9:3:3:1 11-3

-9 of 16 show both dominant traits -3 of 16 show one dom., one recessive -3 of 16 show one rec., one dom. -1 of 16 show both recessive Dihybrid phenotype ratio: 11-3

Law of independent assortment During meiosis, genes for different traits are separated and distributed to gametes independently of one another (if the genes are on different chromosomes). During meiosis, genes for different traits are separated and distributed to gametes independently of one another (if the genes are on different chromosomes). 11-3

The alleles for seed shape segregated independently of those for seed color. Genes that segregate independently do not influence each other's inheritance. 11-3

Trihybrid!

Incomplete Dominance When both alleles contribute to the phenotype of a heterozygous When both alleles contribute to the phenotype of a heterozygous 11-3

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

1:2:1

Codominance 2 dominant alleles are expressed at the same time.. 2 dominant alleles are expressed at the same time

Codominance: roan fur coat 11-3

Codominance: Human blood types 3 Alleles: I A, I B, i 6 genotypes: I A I A, I A I B, I A i, I B I B, I B i, and ii 11-3

Having more than 2 alleles is called Multiple alleles

ABO Blood Group System Genotype Blood Type I A I A or I A i A I B I B or I B i B IAIBIAIBIAIBIAIBAB iiO Multiple alleles: 11-3

Polygenic Traits Polygenic Traits Traits controlled by two or more genes; polygenic traits. Traits controlled by two or more genes; polygenic traits. Skin color in humans. Skin color in humans. 11-3

HumanSkinColor Polygenic Traits

One more thing: X Inactivation in female mammals

In a cross involving two pea plant traits, observation of a 9 : 3 : 3 : 1 ratio in the F 2 generation is evidence for the two traits being inherited together. the two traits being inherited together. an outcome that depends on the sex of the parent plants. an outcome that depends on the sex of the parent plants. the two traits being inherited independently of each other. the two traits being inherited independently of each other. multiple genes being responsible for each trait. multiple genes being responsible for each trait.

Traits controlled by two or more genes are called multiple-allele traits. multiple-allele traits. polygenic traits. polygenic traits. codominant traits. codominant traits. hybrid traits. hybrid traits.

In four o'clock flowers, the alleles for red flowers and white flowers show incomplete dominance. Heterozygous four o'clock plants have pink flowers. pink flowers. white flowers. white flowers. half white flowers and half red flowers. half white flowers and half red flowers. red flowers. red flowers.

A white male horse and a tan female horse produce an offspring that has large areas of white coat and large areas of tan coat. This is an example of incomplete dominance. incomplete dominance. multiple alleles. multiple alleles. codominance. codominance. a polygenic trait. a polygenic trait.

Mendel's principles apply to pea plants only. pea plants only. fruit flies only. fruit flies only. all organisms. all organisms. only plants and animals. only plants and animals.