Of all the differences that distinguish people, the most obvious and most intriguing one is their sex. Cytogenet Gen Res. In an attempt to justify these observations, some researchers have proposed that sexual dimorphism in general is associated with selective cell proliferation [ 74 ].
Curr Top Dev Biol 41— Those identities start to establish themselves in the embryo before the sixth week of pregnancy. Journal of Evolutionary Biology. Novartis Found Symp — discussion —, —, — 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.
Further extensions of the MAT region, possibly involving additional sex-antagonistic genes, led to the U and V chromosomes characterizing male and female gametophytes, as found, e. Sex determination by the whole genome In many animals, sex determination involves the entire genome.
Genomic conflict and transitions in sex determination More generally, selection on the sex ratio can trigger transitions between and among different ESD and GSD systems . Figure 4. Integrative and Comparative Biology. In species with genotypic sex determination, the chromosome pair that determines sex can change rapidly over time.
These theoretical arguments help to account for the prevalence of gynodioecy and the XY chromosome system via pathway 2 observed in plants; nevertheless, all four pathways may be biologically relevant, although no known examples for pathway 4 currently exist.
Reprod Biol Endocrinol 10, 13 Haploid stages n are indicated as shaded areas and diploid stages nn are unshaded. The pairs, right and left, male and female, light and darkness are part of the Pythagorean Table of Opposites. A review lists 12 non-Y-chromosomal genes that are involved in the development of testes, compared with five genes involved in ovary development [ 16 ].