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Chromosomes Reveal the Shared History of Humans and Rhesus Macaques

Male rhesus macaque in Gokarna, Nepal
Research: Genetics & genomics, Evolution & taxonomy

Humans have 46 chromosomes, while rhesus macaques (Macaca mulatta) have 42. Behind that difference lie striking similarities in how their DNA is organised. A new map shows that most rhesus chromosome types correspond to material from a single human chromosome. Some of the exceptions reveal an evolutionary history of chromosomes splitting apart or joining together.

The researchers examined around 3,000 cells from blood samples taken from three male macaques. They used mFISH, a form of “chromosome painting” in which fluorescently labelled DNA probes bind to matching DNA on chromosomes. These probes are short pieces of DNA that identify particular chromosomes by colour. Because the labels were designed for human chromosomes, the colours revealed which parts of the macaque’s genetic material correspond to particular human chromosomes.

Ancient combinations remain visible

The macaque’s 42 chromosomes comprise 20 pairs of autosomes and the sex chromosomes. Counting X and Y separately gives 22 chromosome types. The researchers reported that 16 of these each corresponded to a single human chromosome. Much of the overall organisation of genetic material has therefore been conserved between the two species.

Three macaque chromosomes, however, contain material that lies on two separate chromosomes in humans. Macaque chromosome 2 corresponds to human chromosomes 7 and 21, chromosome 7 to our chromosomes 14 and 15, and chromosome 13 to our chromosomes 20 and 22. Rhesus macaques thus retain older combinations that split in the lineage leading to humans.

For the combination corresponding to human chromosomes 14 and 15, the authors cite earlier research dating the split to about 25 million years ago. The new colour map makes that ancient history visible in chromosomes today.

Two chromosomes became one in humans

Human chromosome 2 tells the opposite story. Its DNA labels attached to two different macaque chromosome pairs: numbers 9 and 15. These correspond to the long and short arms of our chromosome 2, respectively. The pattern reflects the well-known fusion of two ancestral chromosomes that gave rise to human chromosome 2.

The map also helps resolve older disagreements about which chromosomes correspond to one another. Chromosomes can look similar in shape and staining patterns without containing the same genetic material. Comparing DNA content directly helps researchers trace both the conserved features and the larger rearrangements that distinguish primate chromosomes.

Sources and image credit

  1. Nasonova, E., Koshlan, N., & Koshlan, I. (2026). Comparative chromosome analysis of human and rhesus macaque (Macaca mulatta) using human multicolor FISH probes. Natural Science Review, 3, 200805.Primary open-access research article published 11 September 2026; full PDF checked. mFISH was performed on slides from three untreated control males and approximately 3,000 cells were analysed. Sixteen of 22 rhesus chromosome types matched one human chromosome, 13 with the same chromosome number. MMU 2 corresponded to HSA 7+21, MMU 7 to HSA 14+15, and MMU 13 to HSA 20+22; the human chromosome-2 probe labelled MMU 9 and MMU 15, reflecting the human chromosome-2 fusion.

Image: Male rhesus macaque (Macaca mulatta) in Gokarna, Nepal, 17 November 2019. Photo: Charles J. Sharp / Sharp Photography / Wikimedia Commons. CC BY-SA 4.0. Wikimedia Commons Featured Picture and Quality Image; representative species image, not one of the three control males used for mFISH. · CC BY-SA 4.0 · Source

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