Posted by:
Paul Hollander
at Fri May 19 18:42:01 2006 [ Email Message ] [ Show All Posts by Paul Hollander ]
Ian wrote:
>So if I understand your reasoning, because the salmon trait appears to not have a distinct visible homozygous recessive phenotype, it cannot be explained as a codominant trait. Is this correct?
No, this is not correct. Salmon cannot be called a recessive mutant gene because neither a homozygous salmon nor a heterozygous salmon looks normal. If salmon was a recessive mutant gene, heterozygous salmons would look normal.
As salmon is not a recessive mutant gene, it must be some form of dominant mutant gene, where in this case dominant means not recessive. That gives us two choices: dominant or codominant. There seems to be enough overlap of the phenotypes of heterozygous salmons and homozygous salmons to make "dominant" a better choice than "codominant". Go to page 2 of the genetics primer on www.boagenetics.com for a breakdown of how phenotype and genotype determine the classification of dominant, codominant, and recessive mutant genes.
>Haploinsufficiency, basically is a loss of function state. Whereby, the loss of function is variable, which could account for the varying degrees of expression seen in the breedings.
You may be right. But other things that might account for the varying degrees of expression include other genes and environment.
I'm not familiar with the term "haploinsufficiency", and I couldn't find it on www.dictionary.com. For what it's worth, molecular functionality does not have a one to one correlation to whether a mutant is dominant, codominant, or recessive. Albino is a recessive mutant gene with a product that is probably nonfunctional. Is albino also haploinsufficient? And after herpers tried to turn "dominant" into a synonym for "homozygous", I'm scared of giving them any new words to misuse. So at this time, I think there are good reasons not to try to replace "codominant" with "haploinsufficient".
>I'm just trying to understand what criteria were used to determine that the trait was dominant and what the test results were that bear that out.
The breeding data in Rich Ihle's paper in the Journal of Heredity proves that salmon can't be a recessive mutant gene. So it has to be some kind of dominant mutant. With "dominant" meaning "non-recessive" here.
Later Ian wrote:
>I'm just curious what the the phenotype breakdowns have been on the various states. What were the results of a hetero to homozygous dominant? What were the results of a hetero to hetero breeding?
Rich has the results of heterozygous salmon x heterozygous salmon matings in his JoH paper. I don't recall numbers, but some normals were born. The expected genotypes would be 1/4 homozygous salmon, 2/4 heterozygous salmon, 1/4 normal. Rich made one homozygous salmon x normal mating, and all the babies were heterozygous salmons, as expected. He also made one heterozygous salmon x homozygous salmon mating, and all the babies were either homozygous salmons or heterozygous salmons, as expected.
The main thing I question is whether Rich's separation of heterozygous and homozygous salmons is 95% or greater correct. And that would require a lot more breeding tests.
>As I mentioned, I'm just trying to understand the position that this is a dominant trait. If it were, you would expect to see it more often in wild populations than in the rare instances that it does occur.
The frequency of a gene in the wild mostly depends on how long ago the mutation occurred and whether it is beneficial or not. Mutants that are some sort of dominants tend to be lost from the population if they are even a little deleterious. Because there is no reservoir of normal-seeming heterozygotes to keep the mutant gene around.
Paul Hollander
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RE: $64 question on Salmon Boas - Paul Hollander, Fri May 19 18:42:01 2006