On May 29, 2024, a team of researchers from the National Human Genome Research Institute (NHGRI) announced they had generated the first complete chromosome sequences from non-human primates. Published in Nature, these sequences uncover remarkable variation between the Y chromosomes of different species, showing rapid evolution, in addition to revealing previously unstudied regions of great ape genomes. Since these primate species are the closest living relatives to humans, the new sequences can provide insights into human evolution.

The researchers focused on the X and Y chromosomes, which play roles in sexual development and fertility, among many other biological functions. They sequenced chromosomes from five great ape species, chimpanzee, bonobo, gorilla and Bornean and Sumatran orangutans, as

Analyzing these new sequences, the researchers estimated that 62 to 66% of the X chromosomes and 75 to 82% of the Y chromosomes are composed of repetitive DNA sequences. These sequences are much more challenging for scientists to characterize, and studying repetitive DNA has only become possible in recent years due to new DNA sequencing technologies and analysis methods.

The researchers compared the sequences of the ape chromosomes to the human X and Y chromosomes to understand their evolutionary histories. Like the human X and Y, the great ape Y chromosomes have far fewer genes compared to the X chromosomes. The researchers also used a computational method called alignment, which indicates regions of the chromosome that have stayed relatively the same over the course of evolution, revealing the effects of different evolutionary pressures on different parts of the genome.

The researchers found that over 90% of the ape X chromosome sequences aligned to the human X chromosome, showing that the X chromosomes have remained relatively unchanged over millions of years of evolution. However, only 14% to 27% of the ape Y chromosome sequences aligned to the human Y chromosome.well as one other primate species that is more distantly related to humans, the siamang gibbon. A notable difference among the primate Y chromosomes is their length. For example, the Y chromosome from the Sumatran orangutan is twice as long as the gibbon’s Y chromosome. Variation in the number and types of DNA repeats accounts for some of the differences in chromosome lengths.