Epistatic Gene Heredity
Honors Integrated
Overview: Epistasis is the phenomenon where the effects of one gene are modified by
one or several other genes, which are sometimes called modifier genes. The gene whose
phenotype is expressed is said to be epistatic, while the phenotype altered or suppressed
is said to be hypostatic. Epistasis can be contrasted with dominance, which is an
interaction between alleles at the same gene locus. Epistasis is often studied in relation to
Quantitative Trait Loci (QTL) and polygenic inheritance. The key here is that most traits
are polygenetic, i.e. they are determined by more than one gene.
Theoretical: Coat color in Labrador Retrievers is determined by two genes. The first
gene (E or e) is for yellow coat color, and turns off the Black/Chocolate gene (B or b)
when it is homozygous recessive, so the EE and Ee genotypes are both either Black or
Chocolate and the ee combinations are automatically yellow coat phenotypes, regardless
of the BB, Bb, or bb genotypes for the other genes. This is because the ee combination
turns off the other gene so no pigment at all is produced, thus yellow coat. Therefore we
have three Phenotypes and nine genotypes:
EEBB = Black Coat
EeBB = Black Coat
EEBb= Black Coat
EeBb = Black Coat
EEbb = Chocolate Coat
Eebb = Chocolate Coat
eeBB = Yellow Coat
eeBb = Yellow Coat
eebb = Yellow Coat
Task: Cross the following male dog genotype with three female dog genotypes and report
the phenotypes and genotype ratio and percentages from your Punnett’s square.
Male: EeBb
Female#1: eeBB
Female#2: EEBb
Female#3: Eebb
Good Luck!