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

POLYGENIC TRAIT

Sometimes, a trait is controlled

by many genes

Ex. Hair color, eye color, skin

color, Height

Exceptions to Mendel’s principles

MULTIPLE ALLELES

Sometimes, a trait has more

than 2 versions of a gene

Blood Type (A,B, O)

A blending between two phenotypes.

(One allele not completely dominant over

the other.). (2 alleles produce 3

phenotypes.)

Result: Heterozygous phenotype

somewhere in 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

Both phenotypes are fully expressed when

present.

A cross between organisms with two

different phenotypes produces offspring

with has both phenotypes of the parental

traits shown.

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…

YOU tell me which type of

dominance…

Codominance!

Type of

Dominance?

Type of

Dominance?

Incomplete

Dominance!

A Trait found on the X chromosome

Males only need 1 copy of a recessive

allele to to express a sex-linked trait trait

Red Green Colorblindness

Sex-Linked Trait