Figure - PMC

Skip to main content

An official website of the United States government

Here's how you know

Here's how you know

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

View full-text article in PMC

. 2021 Oct 4;10:e67345. doi: 10.7554/eLife.67345

Search in PMC
Search in PubMed
View in NLM Catalog
Add to search

© 2021, Subrini and Turner

This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited.

PMC Copyright notice

Figure 1. — The X and Y chromosomes evolved from a pair of autosomes. First, the testis-determining gene Sry evolved on the proto-Y. Then, successive stratification events occurred, wherein X-Y meiotic recombination arrests along specific regions of the Y, likely due to inversions. The first stratum (i.e. discrete non-recombining region) includes Sry and originated in the last common therian ancestor ~166 million years ago (MYA). After the split from marsupials, the X/Y-added regions (XAR/YAR) fused from an autosome to the sex chromosomes in the eutherian ancestor. A second stratification event occurred independently in both marsupial and eutherian ancestors ~ 97–117 MYA. Concomitantly, in eutherians, a third stratum was formed encompassing the YAR. A fourth and fifth stratum evolved in the ancestor of old-world monkeys ~ 25–44 MYA. Recombination now only occurs within the pseudoautosomal region (PAR).