Introduction:
Sex determination is a highly diversified and fundamentally important process. However, nothing much has been known about the mechanism involved in this diverse sex-determining procedure. A male-determining gene present decides the sex of an individual or a baby on the Y chromosome. However, studies report that the Y chromosome is gradually degenerating and might disappear in the long run. Hence, this extinction of the Y chromosome has paved the way for the evolution of a new sex-determining gene. The most significant fact is that a few branches of rodents have lost their Y chromosomes, but they are alive for further evaluation and research.
How Does the Y Chromosome Help Determine the Sex of an Individual?
Humans or other mammals have almost similar sets of chromosomes. Males have one X and one Y chromosome, whereas females have a pair of X chromosomes. However, the names of these chromosomes have nothing to do with their shapes. The X chromosome comprises 900 genes responsible for various sexual functions. However, the Y chromosome has only 55 genes and numerous non-coding DNA (deoxyribonucleic acid). These non-coding DNA are repetitive and do not perform any significant functions. Hence, the Y chromosome has power-packed genes that initiate the development of male embryos. During the 12th week of conception, the genes present in the Y chromosome or the master genes stimulate the activities of the other genes that regulate testicular development. This testis initiates the formation of the male hormone or testosterone, resulting in the development of a baby boy. The master gene was named the sex region on the Y (SRY) gene in 1990. This gene triggers or stimulates the genetic pathway with the SOX9 gene, which is a key factor in male determination. However, it does not rely on sex chromosomes.
What Is the SRY Gene?
The SRY gene encodes instructions for producing a protein known sex-determining region Y protein. It is responsible for male sex development, which follows a specific pattern based on a person’s chromosome. Normally, 46 chromosomes are present in each cell. Of the 46 chromosomes, the X and Y chromosomes are known as the sex chromosomes. This is because these chromosomes help determine whether the fetus will be male or female. The SRY gene is typically located on the Y chromosome found in males. The SRY gene works as a transcription factor, which implies that it attaches or binds to the specific sites on the DNA. In addition, it regulates the activities of genes. This gene initiates processes that stimulate the development of testicles or male gonads. In addition, the gene prevents the formation of female reproductive structures, including fallopian tubes or the uterus.
What Has Been Known About the Evolution of the New SRY Gene?
Through gene duplication, the SRY gene has arisen from the SOX3 gene bound to the X chromosome. This gene mainly belongs to the SOX family. The duplication has mainly occurred due to a split between a specific class of mammals. Though the SRY gene has evolved quickly, the researchers find it difficult to study its correlation with the sex determination phenomenon. In addition, there are huge differences in the SRY gene activities between species. It is the only gene that has arisen from the original Y chromosome.
What Has Been Known About the Disappearing Y Chromosome?
Most mammals comprise X and Y chromosomes, wherein X has numerous genes, whereas Y has the SRY genes and a few others. Hence, problems arise related to the unequal distribution of X genes in males and females. Studies report that certain mammals, like the platypus, have a completely different set of chromosomes. In such mammals, the XY chromosomes are an ordinary pair with no set of functional genes. Studies report that the Y chromosome has lost numerous active genes over the years of evolution. This loss accounts for about five genes per million years. Hence, researchers predict that the remaining 55 genes will be lost in 11 million years at this rate.
What Do Studies Indicate About Rodents With No Y Chromosomes?
Studies report that rodent lineages who have lost their Y chromosomes are still surviving, which is a ray of hope for most males. Some male species of Japan claim to survive in the absence of Y chromosomes and the SRY gene. However, they have single or double doses of X chromosomes in both sexes. Nothing has been known about sex determination in the absence of the SRY gene. However, researchers report that genes present on the Y chromosomes have been relocated to other chromosomes, but there were no signs of the SRY gene or the presence of its substitute. Certain new sequences have been identified and tested in the genomes of male rats. Tiny differences were noted near the SOX9 gene on chromosome number 3. A small duplication was observed in most males other than females. In addition, the studies suggest that a part of the duplicated DNA contains a switch that turns on the SOX9 gene in response to SRY. The duplication boosts the SOX9 activity, so this change would allow the SOX9 gene to work without the SRY gene.
What Is the Future Outlook of the New Sex-Determining Gene for Males?
The disappearance of the Y chromosome has raised questions about the future of male fertility and sex determination. Some species can synthesize eggs with their own genes via a procedure known as parthenogenesis. However, this is not possible in humans or other mammals. This is because humans have 30 genes that work only when they are transmitted from the male genital tract through a sperm. For reproduction, males and sperm are required, but the disappearance of Y genes could interfere with the survival and existence of the human race. However, the new findings from a study can allow one to heave a sigh of relief. The study suggests that humans are capable enough to give rise to a new sex-determining gene. However, numerous risks are associated with the evolution of a new gene because there might be a possibility of new systems in different parts of the world.
Conclusion:
Numerous studies are being performed to determine the evolution of a new sex-determining gene because of the disappearance of Y chromosomes. However, it is difficult to obtain any conclusive results unless the studies or research have been conducted on most mammals.
