Very good question Kevin, and the answer is yes.



If a male carries the mutation, but never expresses it, then it would be called "sex-limited". If the male expressed it to a lesser degree, or on fewer occasions then it would be "sex-influenced".



There are a few ways I know of which this would occur.



It is possible the female would express the heterozygous version, whereas the male would need to be homozygous to show the mutation. This would become evident through line breeding.



It could also be that a female would express either or both heterozygous/homozygous and the male would express neither.



In either case, this infers the genes are being regulated by hormones, or other gene products that are turned on/off in female development either exclusively, at a different time, or to a greater extent than in males ("epigenetic effects".



Some genes may be turned off specifically depending if they are inherited from either the mother or father, this is called "imprinting" and is a type of epigenetic effect.



Something else that may appear to be this, but is quite different is termed germ-line mosaicism. A fraction of the male sperm, or female eggs, may carry a mutation that other cells don't carry (a very small or even large fraction), this would allow offspring to express phenotypes quite different from parents.



I know that with these possibilities it can be hard to uncover what is going on, but this is what we have to work with. Keeping really good breeding records is very important.



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steve

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