Board Thread:General Discussion/@comment-24351279-20131229004635/@comment-80.112.165.247-20171125235013

As a medical student, I think there are several options to explain this. I'll just explain one to show it can be done.

Females have XX-sex chromosomes, males have XY. The Y has to come from the father, the mother always passes 1 X. Let's assume all the naiad-genes are on the X-chromosome.

There's something called uniparental disomy however, in which one parent passes on two sets of a chromosome (like with down's syndrome, where the kid ends up with triple 21), while the other parent passes on nothing or while the third chromosome gets deleted in order to fix the situation. Look up UPD on wikipedia, they explain it pretty well.

The female naiads might have a mechanism to always pass on both their X-chromosomes and to remove the X passed by the father, or to remove one X of their own in presence of a Y. (wiki: trisomic rescue).

This would explain why all female naiads always pass on the naiad genes, no matter which X chromosome goes to the child. Males only have one X and just like with color blindness, that X's genes will all be expressed since there isn't a second X to compete over dominance.

just one theory.