Mankind: WH(Y) chromosome is disappearing in man?

While there is a lot of talk about the battle of sexes, it’s time one ponders and starts taking the human Y chromosome seriously as its dwindling! Does that mean manhood is about to disappear? Well, from the last decade, the small, stubby Y chromosome is considered as an “empty chromosome” because it is poor in the number genes it houses when compared to the other chromosomes. According to some researchers, it is on a downward trajectory and may completely disappear from the human genome.

Also, more than 50 per cent of the Y chromosome sequence is composed of repeated elements. The Y genes are in continuous decay probably because it does not recombine across its male-specific part, and hence will completely disappear from the human genome.

However, recent advances in genetic technologies have again altered the scientific perspectives about the Y chromosome. Scientists identified that Y chromosome is responsible for important biological roles such as sex determination and male fertility. Recently, scientists found that Y chromosome microdeletions are high in the number of infertile men. The high frequency of Y microdeletions suggests that the Y chromosome is susceptible to spontaneous loss of genetic material. Production of spermatozoa is mainly regulated by Y chromosome specific genes (eg. TTY1,TTY2,PRY, CDY, RBMY, etc). Most of these genes are located in a specific region known as the azoospermia factor region (AZF) in the long arm of the human Y chromosome. The AZF region has four non-overlapping loci-AZFa, AZFb, AZFc, and AZFd. These regions contain important genes such as RBMY, CDY remarkable for their role in germ cell development. The AZF microdeletions are recognized as the most frequent and are the major cause of human male infertility.

Future of men with Y chromosome micro deletion

Before the development of Assisted reproductive technology (ART) with intracytoplasmic sperm injection (ICSI) and sperm retrieval techniques, such as multiple testicular sperm extraction (TESE), most patients with Y chromosome micro deletions were not able to conceive. However, with these techniques successful pregnancies are possible. However, this technique may allow the transmission of Y chromosome micro deletion to the next generation. Therefore, a potential of advanced genetic testing is required for the treatment of Y chromosome micro deletion.
Y chromosome is not only specific to sex determination and spermatogenesis. New scientific evidence in a review of Nature publishing group supports the theories about the potential role played by the genetic variation within the Y chromosome. It influences the immune system and inflammatory responses in men which is determining their susceptibility to disease.

Recently, it was proved that a range of environmental exposures is associated with reduced sperm concentration and quality. This is due to the Y chromosome genes being affected. In future, prolonged environmental exposure (industrial chemicals, heavy metal exposure, heat, radiation, and trauma) and unfavourable lifestyle (illicit drug use, alcohol consumption, tobacco chewing and smoking, stress, obesity) will result in loss of expression of critical genes present in the Y chromosome. We have been working on male reproductive genetics at VIT, Vellore, for the past 10 years. The aim of our research is to unravel the relationship between environment, lifestyle, the Y chromosome and related pathophysiology to provide new insights into the complex evolution and relevance of the Y chromosome in human health.

(Dr. V.G.Abilash works as a Senior Assistant Professor, Department of Biomedical Sciences, School of BioSciences and Technology (SBST), Vellore Institute Technology (VIT), Vellore,Tamil Nadu and Shalaka Sudhir Ramgir, is a teacher-cum-research assistant at VIT.)

• Y-linked genes will lose their expressions due to prolonged environmental exposure (industrial chemicals, heavy metal exposure, heat, radiation, and trauma)
• Lifestyle factors (illicit drug use, alcohol consumption, tobacco chewing and smoking, stress, obesity) also affect the Y-linked genes.