Epistasis: Two different genes work together in harmony to create on phenotype. For example, in labs the genes for melanin production (B for black and b for brown) and deposition (E for deposition and e for no deposition) both help determine what color the lab will be (black, chocolate, or yellow). Black labs are heterozygous or homozygous dominant for both. Chocolate labs are homozygous recessive for production but heterozygous or homozygous dominant for deposition. Yellow labs just need to be homozygous recessive for deposition. With that, you can figure out the genotypes for these dogs and the ratios of breeding and such.
Incomplete dominance: Both alleles in a heterozygous organism may be expressed in the phenotype. Examples include palomino horses and tortoiseshell cats, where having both alleles will make them a new color instead of the color they would be homozygous for either allele (tortoiseshell instead of brown or black)
Codominance: A single gene has more than one dominant allele. For example, in blood type both types A and B are dominant over type O. So if you had AO, you would just be type A. However, if you have both type A and B, you would have type AB blood. Simple as that.
Sex-linked: A gene is carried only on the x-chromosome, so males are more likely to get the disorder because they only have one X. An example is colorblindness, which is rare in females but very common in males. Females are normally only the carriers.
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