>Since this stuff gets pretty deep and I have always had a hard time finding my way through it I have a question that you can probably answer...



I'm usually willing to discuss genetics questions. Sometimes I can answer them, and sometimes I can't.



Actually, anyone who can understand how flipping two coins can produce four possible outcomes (2 heads, 2 tails, head & tails, tails & head) can understand genetics. It just has to be worked up to, like swimming. Some of these discussions are like getting shoved into the deep end of the pool.



>Does a gene modifer have to be on the same loci as the gene that it modifies? My hunch had to do with a gene modifier but I don't have the knowledge to fully explain this idea.



I was taught that a modifier gene is a mutant gene which has an effect that is invisible in an otherwise normal animal. The modifier changes the physical effect caused by another mutant gene.



Many years ago a man named Castle took a stock of hooded rats. Hooded is a recessive mutant gene. Hooded rats have pigment on the head, shoulders, and along the spine while the rest of the rat is pigmentless (white). Castle divided the rat stock and over generations selected the most pigmented in one stock and the least pigmented in the other stock. Eventually he had two stocks. One stock was pigmented over the whole body except a bit on the belly. The second stock was white except for spots on the head. When the two stocks were mated together, the babies were hooded like the original stock. Castle's explanation was that modifier genes had affected the expression of the hooded mutant gene.



All of those rats had a pair of hooded genes at the hooded locus (Locus singular, loci plural. Latin.) The modifier genes had to be at other loci, probably several other loci.



>You made very valid points and I agree with them completely. All that is assuming that the cause of this mutation lies on one locus only.



The breeding results so far can be explained using one locus. But there have only been three or four matings with an unknown (by me) number of babies. More data may require changing the explanation. We'll have to wait and see.



Paul Hollander

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