You are currently viewing 📰 Is the evolution of sex chromosomes really linked to the differences between males and females?

📰 Is the evolution of sex chromosomes really linked to the differences between males and females?

The sex chromosomes are often highly differentiated, like the X and Y chromosomes in humans, the Y chromosome being very small. A new mathematical model shows that arresting recombination between sex chromosomes, allowing their differentiation, may simply evolve to harbor deleterious mutations that naturally segregate in genomes rather than due to differences between males and females. This article was published in PLoS Biology.


Chromosomes. © fpm – iStock

Genetic exchanges between chromosomes inherited from both parents are beneficial in the long term, because they allow greater efficiency of the natural selection (In biology, natural selection is one of the mechanisms that guides evolution…) to promote beneficial mutations and eliminate deleterious mutations. Despite these advantages, local deletions of gene exchange are often observed, particularly on the sex chromosomes. the chromosome (The chromosome (from the Greek khroma, color and soma, body, element) is the element…) Y for example in the human being has stopped its genetic exchanges with the X chromosome (The X chromosome is one of the two sex chromosomes in humans and some animals…) for several million years and, because of the reduction in the efficiency of selection that this has caused, it has accumulated deleterious mutations and lost many genes. It has long been accepted that the cessation of genetic exchange between the X and Y chromosomes, although apparently deleterious in the long term, was favored by natural selection because it allowed the emergence and maintenance of differences between males and females. However, this theoretical hypothesis is not supported by the data (In information technology (IT), data is an elementary description, often…) empirical. Notably, the chromosomes of fungal sex types also show repeated arrests of recombination despite the absence of male or female (In biology, female (from the Latin “femella”, little woman, young woman) is the…).

Scientists have developed a mathematical model (A mathematical model is a translation of reality to be able to apply the tools to it,…) showing that stopping recombination between sex chromosomes can evolve simply because it prevents the expression of deleterious mutations, naturally present in large genomes number (The notion of number in linguistics is treated in the article “Number…). This hypothesis is based on very simple mechanisms of genetic (Genetics (from the Greek genno γεννώ = to give birth) is…)does not require the existence of differences between males and females or compensation for dosage (In analytical chemistry, dosage is the action of determining the amount…) of expression, and thus provides a simple, general, and powerful mechanism for explaining the evolution of sex chromosomes and other genetic structures without recombination in many species, including fungi.

Many recessive deleterious mutations segregate in natural populations (in red). If a chromosomal inversion capture (A capture, in the field of astronautics, is a process by which a celestial object, which…) fewer deleterious mutations than mean (The average is a statistical measure characterizing the elements of a set of…) of the population on this segment, it has an advantage and will be selected. However, if it increases in frequency (In physics, frequency generally refers to the measurement of the number of times a…)she will find herself time (Time is a concept developed by human beings to apprehend the…) time in the homozygous state, and the recessive deleterious mutations will be expressed, preventing the inversion from being fixed in the population. But if the inversion also captures a locus of the determinism (Determinism is a philosophical notion that every event is…) from sex (The word sex often designates the reproductive system, or the sexual act and the…) which is always in the heterozygous state, for example the embarrassed (A gene is a deoxyribonucleic acid (DNA) sequence that specifies the…) determining the male sex on a Y chromosome, the deleterious mutations carried by the inversion will also always be in the heterozygous state, and therefore always sheltered from selection; the inversion will then fix itself, thus suppressing the recombination between the X and Y chromosomes.

CNRS laboratories involved:
– Ecology Systematic (In the life sciences and in natural history, systematics is the science which has for…) and Evolution (ESE – CNRS / AgroParisTech / University (A university is an institution of higher education whose objective is the…) Paris-Saclay)
– Evolution, Ecology and Paleontology (Paleontology is the science that studies the fossil remains of living things in the world…) (Evo-Eco-Paleo – CNRS / University of Lille)
– Mathematics applied to Paris (Paris is a French city, capital of France and the capital of the region…) 5 (MAP5 – CNRS / Paris City University)

Reference:
Paul Jay, Emilie Tezenas, Amandine Véber, Tatiana Giraud. Sheltering of deleterious mutations explains the stepwise extension of recombination suppression on sex chromosomes and other supergenes. Plos Biology. 2022.

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