Humans and many mammals have an XY sex determination system. This means that the presence of a Y chromosome makes an individual male, while having 2 X chomosomes (and lacking a Y chomosome) makes an individual female. Birds and other species have a ZW sex determination system, where the presence of a W chromosome makes an individual female.
In my Gyre world, I have used the XY sex determination system to add sexual morphs. Male morphs are easy: Unicorns have an X and a U chromosome. Functionally the U chromosome is a Y chromosome, except that it is larger than the X chromosome, and it carries the sex-determining SRY gene, along with other genes that make the child carrying it develop into a unicorn in-utero. Wyrms are similar, having an X and a D chromosome.
This works out 'easily' since sex determination with normal men is:
XX x XY = ½ XX, ½ XY
Substitute Y with U or D, and it still works. Of course, unicorns and wyrms must mate with women in order to reproduce, but the gender balance is preserved. Unicorns and wyrms are simply male morphs. In the ZW sex determination system, female morphs would be 'easy' to implement by replacing the W chromosome, as females are ZW while males are ZZ.
However, when it comes to chromosomally inherited female sexual morphs in humans, it is not so easy. To use the example of lilim, which are women who have batlike wings and taloned feet, lilim have X and L chromosomes, where the L chromosome functions similarly to an X chromosome. This lack of ease would also apply to males in the ZW determination system. The genetics work out as:
XL x XY = ¼ XX, ¼ XY, ¼ XL, ¼ LY
So, we can see that we have an unwanted LY offspring... what can we do with it? Make LY a lethal result? Make it into yet another male morph or have it be functionally identical to XY males, which would further complicate the genetics:
XX x LY = ½ XL, ½ XY
XL x LY = ¼ XL, ¼ XY, ¼ LL, ¼ LY
From which we get LL, which is an additional complication:
LL x XY = ½LX, ½LY
LL x LY = ½LL, ½LY
So, if we also allow LY males and homozygous lilim, we end up with lilim only sometimes breeding true, and sometimes seeming to skip a generation... which is fine as long as that's what you want, but I didn't want that.
In my Lilim, I went with making LY lethal, though LXY, which involves a rare error during the process of meiosis, results in an infertile male lilim. However, this means that the viable offspring then become 1/3 female, 1/3 male and 1/3 lilim. Since women and lilim are female, this upsets the 50% gender balance and makes lilim less fertile than women, and unless lilim are more desirable as mates than women, will lead to extinction of the morph.
So, after all that background, is there any way that I can have an 'easy' genetically-based female-only morph where the female morph reproduces only itself 50% or 50% normal non-carrier males, where the morph can not skip generations?
It need not be a sex-chromosome-based system like the lilim, but I would prefer some sort of chromosome-based system where the morph is carried on the chromosome.
This question is similar to How to get the Lilim to breed true?, but differs in that I'm asking about any way that a female morph can breed true, rather than only the ways that lilim can be modified to breed true.
It need not be a sex-chromosome-based system
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