A recent study conducted by scientists has revealed that the Y chromosome in all primates, such as chimpanzees, gorillas, orangutans, bonobos is evolving at a much faster rate than other chromosomes.
Due to this, while overall, the DNA of these primates is very similar to humans, only 15%-30% of the genetic material of the Y chromosomes is similar.
Introduction
You would have learnt in school that humans have 23 pairs of chromosomes in all, out of which one is the pair of sex chromosome, that defines the sex of the person. You would also have learnt that each baby gets an X chromosome from its mother, and the chromosome from the father (X or Y), determines the sex.
If the chromosome inherited from the father is an Y chromosome, the baby will be a boy. If the chromosome is X, the baby will be a girl.
Now, something that you would not have learnt in school is that all apes, for example, chimpanzees, gorrilas, baboons, etc, also have similar sex chromosomes to humans.
What Was Found?
Out of all apes, Chimpanzees are genetically the most similar to humans, sharing more than 98% of their DNA(1) across the whole genome(2). However, only 14%-27% of DNA in the Y chromosomes of Chimps and humans are common.
This implies that the Y chromosomes have been evolving way faster than the whole genome taken as a whole.
How Did They Find Out?
The scientists compared the sex chromosomes of 6 primate species, i.e. chimpanzees (Pan troglodytes), bonobos (Pan paniscus), western lowland gorillas (Gorilla gorilla gorilla), Bornean and Sumatran orangutans (Pongo pygmaeus and Pongo abelii) and the more distantly related to humans, siamang gibbons (Symphalangus syndactylus).
Credit: Britannica.
Scientists used a method called T2T (Telomere-to-Telomere) sequencing to study the chromosomes. This is a relatively new method of reading DNA strings. In very simple terms, this method reads the DNA strand continuously from one end of the chromosome to the other, including its tips, which are called telomeres.
The results were then compared using software, to reveal which parts of the chromosome had changed and which parts had remained the same. The X and Y chromosomal sequences of each of the six species were also compared with the human X and Y chromosomes, which had been sequenced in an earlier study using the T2T method.
What Did They Find?
The study showed that in all of the species which were studied, the Y chromosome evolved rapidly. Even species in the same genus(3) have quite different Y chromosomes.
For example, chimpanzees and bonobos, which diverged from the same species only 1-2 million years ago (very less time ago, in evolutionary terms), have a dramatic difference in the lengths of their Y chromosomes.
Another find was that the X chromosome is very similar thorughout the primate species, probably because of the role it plays in reproduction.
Why Is The Y Chromosome Evolving So Much?
The reason for this fast evolution could be that the Y chromosome produces so many sperms, which requires a lot of cell division, where mistakes in the DNA copying could creep in.
These mistakes are known as mutations, which ultimately lead to evolution.
Limitations Of The Study
One limitation of this study is that it looked at only one member of each primate species, so it cannot say how much the Y chromosome varies among members of the same species.
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Cheers
Aarav Iyer
Glossary
(1) DNA- Deoxyribonucleic Acid, a molecule that contains all the
genetic material responsible for the function of an organism.
(2) Genome- A genome is the complete set of genetic matter in an
organism.
(3) Genus- It is a taxonimic group of organisms covering more than one
species. It can also be referred to as a sub-family.
References:
(1)
LiveScience
(2)
Nature