In mosses or liverworts, separate sexes are only found in the haploid phase of the life cycle of an individual UV sex chromosomes. Exactly how the environment triggers sex development has remained an open question, although a recent study found that methylation provided the link in European sea bass .
I see the point here, if you have a little girl. As the facts stand this is all there is XX and XY. Citing articles via Web of Science Some ideas of the diversity of sex determining genes among medaka given. The zero sometimes, the letter O signifies the lack of a second X.
Instead, evolutionary traps may stabilize sex-determining systems for long spans of evolutionary time. Cho S, Huang ZY, Zhang J Sex-specific splicing of the honeybee doublesex gene reveals million years of evolution at the bottom of the insect sex-determination pathway.
Thus, while sex determination is generally characterized by diversity and turnover, some sex-determining systems appear to be more evolutionarily stable than others . Letters ZZ, ZW indicate sex chromosomes.
The first hypothesis is that there are trade-offs between male and female function, such as when mating displays enhance male fitness but decrease female fitness. For example, if an allele of an autosomal gene is beneficial to males but harmful to females and becomes linked to a dominant masculinizing mutation, then chromosomes that carry both the male-beneficial and male-dominant alleles create a novel Y that can replace the ancestral mechanisms.
Androdioecy: a breeding system that consists of a mixture of males and hermaphrodites. Licensee IntechOpen. Retrieved 8 December
A few key examples tend to predominate: the ZW system in birds, XO in insects, haplodiploidy, and environmental sex determination systems. However, these model organisms present a false impression of stability in how sex is determined, and their commonalities mask the diversity and turnover in sex determination mechanisms that is readily apparent when taking a broader taxonomic view.
Thus, all it takes is a small genetic change to turn SRY, or any of the genes it targets, on or off.