Quote:
Originally Posted by dosthouhavemilk
There was one study done on a closely bred group of Saanens(?) back in the early 70s, I believe it was, that indicated that the Polled gene can carry alongside it a gene for hermaphroditism. Which is why the polled was culled out of a lot of the dairy breeds and why there is some stigma attached to polled goats.
There are breeders who regularly breed polled to polled and have no more hermies than when they breed horned to horned.
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There are two major ways of getting genes mixed in animals. The most common, is that for each chromasome strand, the neborn will either get a strand from its grand mother or grandfather (on both sides). Since their are 60 chromosomes it it will have a 50-50 chance of getting any one chromosome from it paternal grand mother, and a 50-50 percent chance of getting any on chromasome from it paternal grandfather ( some with maternal grand mother and grand father) This however limits the gene mixing that can take place, because, barring mutations, all the genes on a given parental chromasome would always be the same.
How nature gets around this, is that when the chomasome strands containing the genes unwind (in the formation of eggs or sperm, which only get one side of the chromasome pair) sometimes there is a place where they cross each other before they fully get untangled, and they swap one end of the chromasome pair with the other side. This is much easier to show in a picture than to explain with words.
For example, in the formation of an egg, under usually circumstances, when one of those 60 chromasome pairs unwind, the egg would get either the exact grandmothers or grandfathers original side of that pair. If, however, when they are undwinding, they snag at some point, and swap ends, each of the chromasome pairs will have one end of the grandmothers chromoasome and the other end will be the grandfathers chromasome. (same with the other side of the pair except it will have opposite ends)
This allows a lot more genetic diversity.
What this means though, is that the genes that are close on a chromasome, have much less chance of being seperated than genes farther away. If there was a defective gene for hermaphroditism, that was within a few genes of the polled gene, then the chances of swapping ends in between them is very reduced. It can be seen that the last genes on either end of the chromosome would always be changed if there was a swap. However, the closer any two genes would be together on the stran, the less chance they would have to be swapped, because the breaking point would have to, by chance, be between them.
Once this happened, if it was recognized, all the offspring of the one carrying polled but not hermaphroditism, would have no trouble, nor would they pass it along.
*The genes on the sex chromosome have their own special interaction, so this description may not necessarily apply. That is where "sex-linked" comes in. One side of the sex chomasome does not have a corresponing paired side.
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