Heredity III: Incomplete Dominance and Epistasis

Updated: Feb 27

The Heredity III virtual lab tests one trait...with five possible phenotypes. This has a little more going on than the Heredity I and Heredity II simulations. This post will offer an explanation of the inheritance of fur color in this species.


There are two separate genes involved here. They are both autosomal and are on different chromosomes. The first gene, which I'll call the primary color gene, has two alleles red and blue. For the sake of this explanation, I'll label these R and B. This gene demonstrates incomplete dominance. For the sake of this explanation, I'll label these R and B. The red phenotype results from two red alleles (RR), the blue phenotype results from two blue alleles (BB) and heterozygotes (RB) are purple.

Incomplete dominance phenotypes and genotypes

The P generation options are all homozygous, so there are no purple individuals available for P generation crosses. By selecting red and blue individuals for the P generation cross, the user can get data for the incomplete dominance example without having to worry about the epistasis aspect of the simulation.


P generation options for the Heredity III simulation

The brown and gray colors result from a second gene, which I'll call the alteration gene. This gene also has two alleles, one dominant (A) and one recessive (a) If an individual has two recessive copies of the gene, then they will be either red, purple, or blue depending on the genotype of the primary color gene. A dominant copy of the alteration gene will result in brown if an R allele is present for the primary color gene and gray if the primary color gene genotype is BB.

Phenotypes and genotypes for epistasis example. R_ indicates that the genotype can be RR or RB and A_ indicates that the genoytpe can be AA or Aa.

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