About two years ago, a study was published revealing that in two rodent species — the Eastern European wolf and the spiny rats of Japan — the Y chromosome has disappeared. The research also indicated that these two rodent species have developed a new sex-determining mechanism in another chromosome, where the SRY gene, which typically determines male sex on the Y chromosome, has been relocated. Despite the disappearance of the Y chromosome in these species, males are still being produced because the sex-determining function has been transferred to another chromosome.
In humans, the Y-chromosome is about one-third the size of the X chromosome and contains around 100 genes. In comparison, the X chromosome, which is present in females, has about 900 genes. Over the years, approximately 90% of the genes on the Y chromosome have been lost, and now only about 55 genes remain. It is estimated that it will take another 10-11 million years for the Y chromosome to potentially lose all of its genes.
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