Incomplete Dominance & Codominance

Section 11-3 in Book

Review of Mendel’s Principles

Genes are passed parents offspring; get one allele from each parent

During Meiosis, the alleles for a gene segregate from each other.

During Meiosis, genes independently assort with each other.

Exceptions to Mendel’s principles

Sometimes, there is no dominant or recessive gene, or the trait is controlled by many alleles or genes.

Neither allele is dominant Heterozygous phenotype produces 3rd phenotype

somewhere between homozygous phenotype.

Incomplete Dominance

1. Incomplete Dominance

Examples: Trait: Flower Color

Expressions: Red x White Pink

RR= Red; RW= pink; WW= white

straight hair, wavy, curly

Incomplete Dominance

In codominance, both alleles are dominant and are expressed in heterozygous organisms.

Codominance

2. Codominance Both alleles contribute to the phenotype.

Example: In come chickens

Black Chicken x White Speckled Chicken

YOU tell me which type of dominance…

Codominance!

Type of Dominance?

Incomplete Dominance!

Type of Dominance?

Incomplete Dominance!

Multiple Alleles

Gene has more than two alleles. Ex. Blood type in humans

Polygenic Traits

Trait controlled by two or more genes Ex. Skin color of humans (4 different

genes) Reddish-brown eyes of fruit flies

Sex-Linked Genes/Traits

Special pattern of inheritance for genes located on the X and Y chromosomes.

Y chromosome is very small only holds a few genes

3 human genes associated with color vision are on the X chromosome.

In males, a defected version of these genes produces colorblindness.

Why the difference? Males only have one X chromosome.

Pedigree