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Non-allelic or non-alletic

I stumbled across the term in my Human Genetics textbook. It didn't explain it there, and a quick google search only showed scientific papers that refer to 'recombinations with non-allelic genes' without explaining what they are.

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It is my understanding that a non-allelic gene is one that affects another's traits, but is not as a typical dominant / recessive manner. If I am correct, this is the same thing as epistasis - meaning that one gene modifies how another is expressed. There exists epistatic genes for horse coat color. One gene is the coat color itself (horses may have either brown or red color alleles at this loci), the second gene is for a protein that allows the coat color gene to be expressed. For example, a horse has two brown alleles at the coat color locus. It also has a wild type gene in the second (modifier) position. This modifier allows the color brown to be expressed and the horse is brown. B/B, wt/wt --> Brown If the horse has the two brown alleles, but has a mutant allele at the modifier position, then coat color is not expressed and the horse is white. B/B, mt/mt --> white

Because the modifier alleles are separate genes from the coat color alleles, the two are non-allelic - yet they both affect the same trait in some way.

I hope this helps.

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+1 This is also my understanding of terdon's link. I would argue that the name non-allelic gene is very poorly chosen though. Theoretically speaking there might not have any single gene that does not affect the phenotypic expression of other genes. And of course a non-allelic gene can be a non-allelic gene only if it is polymorphic (and have multiple alleles)! –  Remi.b Nov 28 '13 at 8:04

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