.9ma HSA2 fusion 23 paired chromosomes in human, 24 in arboreal great apes

BMC Genomics volume 23, Article number: 616 (2022)

Abstract
Background
The reduction of the chromosome number from 48 in the Great Apes to 46 in modern humans is thought to result from the end-to-end fusion of two ancestral non-human primate chromosomes forming the human chromosome 2 (HSA2). Genomic signatures of this

event are the presence of inverted telomeric repeats at the HSA2 fusion site and a block of degenerate satellite sequences that mark the remnants of the ancestral centromere. It has been estimated that this fusion arose up to 4.5 million years ago (Mya).

Results
We have developed an enhanced algorithm for the detection and efficient counting of the locally over-represented weak-to-strong (AT to GC) substitutions. By analyzing the enrichment of these substitutions around the fusion site of HSA2 we estimated

its formation time at 0.9 Mya with a 95% confidence interval of 0.4-1.5 Mya. Additionally, based on the statistics derived from our algorithm, we have reconstructed the evolutionary distances among the Great Apes (Hominoidea).

Conclusions
Our results shed light on the HSA2 fusion formation and provide a novel computational alternative for the estimation of the speciation chronology

https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-022-08828-7

.

On a related topic, some AMH's have only 44 chromosomes:

<https://www.thetech.org/ask-a-geneticist/48-46>

I'm sure a few have other aberrant counts.

<https://www.kqed.org/quest/5239/and-then-there-were-44>

<https://www.kqed.org/quest/586/chromosome-fusion-chance-or-design>

The arboreal Great Apes have a stable 48 and limited largely to tropical swamp forests, AMHs has a stable 46 and has overrun the planet despite serious birthing difficulties, in part due to broad shoulders and big head fitting through a birth canal

modified for obligate terrestrial striding bipedalism.

...

Malaria & ABO blood: Type O protects against worse damage
Pan & Hs & malaria species:
- Hs are the only primates missing N-glycolyl neuraminic acid Neu5Gc ;
- Hs cells are instead rich in N-acetyl neuraminic acid Neu5Ac ;
- the enzyme that converts Neu5Ac to Neu5Gc is disabled by mutation in Hs. The explanation for this loss might be malaria:
- Pt don't get sick from the Hs malaria parasite Plasmodium falciparum (favours Neu5Ac).
- Hs can't be infected with the Pt parasite Plasm.reichenowi (prefers Neu5Gc on Pt RBCs).

I thought the Neu5Ac/Neu5Gc change was unique to humans, but it has happened to a variety of mammals:
https://www.frontiersin.org/articles/10.3389/fimmu.2019.00789/full
Seals, white-tail deer, spider monkeys, weasels, raccoons etc.

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