Notes: Incomplete Dominance Phenotype is affected by many different factors.

Phenotype can depend on interactions of alleles.

• In incomplete dominance, neither allele is completely dominant nor completely recessive.

– Heterozygous phenotype is a blend between the two homozygous phenotypes

– Homozygous parental phenotypes not seen in F1 offspring

Four o’clock plants aka Carnations

• Homozygous plants are either red (RR) or white (R’R’).

• Heterozygous (RR’) are pink.

This animation shows the cross between a black homozygous

dominant cat and a white homozygous recessive cat. This

results in a litter of all heterozygous gray cats.

• Codominant alleles will both be completely expressed.

– Codominant alleles are neither dominant nor recessive.

– The ABO blood types result from codominant alleles.

This animation shows the cross between a black homozygous recessive cat and a white homozygous dominant cat. This results in a heterozygous litter of black and white spotted kittens.

Codominance

• Multiple alleles: exists when genes have more than two alleles

– The ABO blood types result from multiple alleles that are codominant

Many genes may interact to produce one trait.

• Polygenic traits are produced by two or more genes.

Order of dominance: brown > green > blue.

• An epistatic gene can interfere with other genes by overshadowing them for a particular trait.

Labrador Retriever Genetics

• Black is dominant to chocolate B or b

• Yellow is recessive epistatic (when present, it blocks the

expression of the black and chocolate alleles) E or e

Phenotype Possible Genotypes

BBEE BbEE

BBEe BbEe

bbEE bbEe

Bbee Bbee

bbee

The environment interacts with genotype.

• Examples: • sex of sea turtles depends on both genes and temperature

• Phenotype is a combination of genotype and environment.