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Some time ago I came across two facts regarding the X and Y chromosomes. First, they show a much higher rate of mutation than the other chromosomes and secondly, of all the chromosomes the X and Y chromosomes of chimpanzees are the most different from their human counterparts (here's a reference regarding at least the Y chromosome) and in fact besides those that determine sexual organs and sexual differences between males and females as is common among most mammals, they are completely different in the two species. This led me to the conclusion that the X and Y chromosomes are the "avant-garde" of the genome. It is here I thought, where genetic innovation most often occurs. The weird difference between the X and Y chromosome in comparison to each other and any of the other pairs, made sense to me too, because perhaps residing on the Y chromosome made for radical testing of the contributions to fitness the genes made in that the genes on the Y chromosome have no duplicates on the X chromosome with which to cross over or be attenuated by unmutated copies.
Since the Y and less so the X chromosomes in mammals show a higher rate of mutation than the rest of the chromosomes, the male and female sexes in mammals and perhaps other organisms are seen as the "research department" of the organism. That is genes that the animal is testing out to see whether they increase fitness are concentrated on the Y chromosome and less so on the X. Moreover it is suggested that promising mutations from other chromosomes may be moved first to the Y chromosome to be tested. The advantage of using the Y chromosome is that it has no moderating unmutated duplicate copies on the other chromosome, so whatever effect the new gene has, it is all by itself affecting the fitness of the organism.
Of course, the genes to be tested on the Y chromosome would only be expressed 50% of the time. This is useful in that if the new gene kills the organism, it would only happen with males.
I propose further that if the gene "has proven itself" by continuing to exist over many generations, it could then jump to the X chromosome. From there it would again be expressed at the same levels with the male, but with females, the gene would sometimes be turned off and if one of the copies reverts to an unmutated state, the gene would not be tested in 100% of the organisms, but in 75%.
In fact, maybe the genes start first on the X with one copy where it is turned off half the time, leading it to be expressed 25% of the time. Next, the gene proven to have increased fitness by the mere fact of continuing to exist over a certain number of generations would jump to the Y chromosome. Here it would be expressed 50% of the time among the young. After several more generations of proving itself, the gene would jump back to the X chromosome, be duplicated and somehow maybe one of the copies is unmutated so that when under normal silencing of one of the genes of the female, the new gene would be expressed 75% of the time.
As for the mechanism for tracking how many generations a new gene undergoes, perhaps each generation the gene might move toward the centromere and when it reaches it, it is transferred to the other sex chromosome. Or conversely, it could start at the centromere and move out toward the tip and when it reaches the tip, it would jump to the other sex chromosome.
Finally in this speculative scheme, once the gene has lived long enough under 75% expression, it would be seen as vetted by the cell and moved to a non-sex chromosome.