“Male Y chromosomes are usually composed almost entirely of repetitive transposons, fragments of the genomes of ancient viruses. These DNA regions in young cells are blocked by the protein "wrapper" of chromosomes, but with age its structure weakens. As a result, these areas are activated, which has a negative effect on the cells,” the researchers write.
All mammals, many species of birds and insects use special chromosomes to determine the sex of future offspring. For example, girls have two X chromosomes, while boys have one X and one Y chromosomes. Scientists do not know yet where the male and female embryo growth programs are contained and what controls them.
Recent studies show that during the evolution of mammals, the Y chromosome decreases rather rapidly, which means that it can disappear entirely. The experiments on mice show that a full-fledged male organism can be grown without the Y chromosome in the cells of the embryo: for this you need to take only two genes from it and transfer them to other regions of the genome.
Photos are from open sources.