Jun 1, 2007 · The X and Y chromosomes of today's mammals originated from an ordinary autosomal pair, which became differentiated as the Y chromosome progressively degraded, losing practically all …

The Y chromosome, which distinguishes males from females at the genetic level, appeared some 180 million years ago. It originated twice independently in all mammals.

The crown group mammals, sometimes called 'true mammals', are the extant mammals and their close relatives back to their last common ancestor. Since this group has living members, DNA analysis can …

In all vertebrate embryos, certain cells are singled out early in development as progenitors of the gametes. These primordial germ cells migrate to the developing gonads, which will form the ovaries …

Jun 13, 2016 · Mammals don't start as females, they start as a blank slate with XX or XY genetic code, and for the first 5-6 weeks of gestation only the X gene expresses.

May 7, 2025 · The evolutionary journey from single-gender replication to the introduction of males suggests that “female-first” may not be metaphorical but a biological reality.

Jun 3, 2021 · Our findings suggest that differences in resource availability affect female distribution, which ultimately leads to intraspecific variation in male reproductive tactics and sexual morphology.

Nov 2, 2023 · The researchers further learned that these differences between the sexes occur across mammals in the same organs and the same cell types in these organs; but they mostly occur through …

Sep 5, 2006 · The problem of the genetic cost of sex does not apply to its origin in the first place. Regular sexual reproduction first evolved among single-celled eukaryotes, which lacked any …

Mammals evolved from therapsids in the late Triassic period, as the earliest known mammal fossils are from the early Jurassic period, some 205 million years ago.