The Future of Sex for Men from a Genetic Perspective

In the last few years that there has been a serious decline in the sperm count for men. Infertility among men is on the rise.The human sperm stands apart from the sex cells of virtually all other mammals in its low number of characteristics, smaller number of functions, and their sensitivity to environmental hazards. The fusion of sperm with egg cell is becoming increasingly difficult. Roughly one in seven Western couples seek some kind of treatment for infertility, mostly because of poor sperm quality.

Even when there is a successful union of sperm and egg; mutations and defects will crop up in the next generation. Many of the mutations that occur appears to have come from the sperm. For example, children from fathers who are heavy smokers generally have a four times higher risk of developing cancer.

The impact of chemicals in the environment and the inherited tendency to produce low sperm count are compounded by the advent of effective contraception and the introduction of the new technology, assisted-conception such as in-vitro fertilization. Consequently, men with high sperm count have lost their advantage over those with low sperm count. As a result, future generations will consist of more men with poor sperm quality and low sperm production. This will ultimately cause a further decline in sperm quality and human fertility.

What are causing these poor fertilizing potentials and genetic damages in the sperms? Two main causes are gene deletions on the long arm of Y-Chromosomes and oxidative stress.

Take a look at the photo below. These are the chromosomes from a man since there is an X and Y-chromosome present. Female has two X-chromosomes. Notice how short the Y- chromosome (from the male) is with respect to the X-chromosome. Also keep in mine that all chromosomes come in pairs with both halves or arms being the same length with the exception of the male Y-chromosome. The other arm is a backup copy. In the male chromosome one arm is much shorter than the other arm. This means that all the genes on one arm is not present on the other arm. Therefore, if there is a defective or missing gene on the long arm, there will not be a backup copy of that defective or missing gene on the short arm because it is simply not there. When this happen the Y-chromosome is no longer a matching partner for the X-chromosome from the female and conception will not occur.

The Y-chromosome use to be same size as the X-chromosome about 300 million years ago until it lost a piece here and there over all that time, but it managed to get large additions of genes (sections of chromosomes) from non-sex determining chromosomes. Also many of its remaining genes have acquired functions necessary for sex determination and sperm production; to be able to combine with the X-chromosome for fertilization to take place.

The Y-chromosome originally had 1,500 genes but over the last 300 million years about 50 were inactivated or lost. That means the Y-chromosome have lost about five genes for every million years. The Y-chromosome is still losing genes today, which mean eventually at this rate the Y-chromosome in the human male will self-destruct or become useless in about 10 million years. This has already occurred in the mole vole, in which the Y-chromosome is completely gone. Men who are severely infertile, 5 to 15% of them experience infertility due to degeneration of their Y-chromosome because there is a substantial amount of gene deletion occurring there. Gene deletion is caused by DNA damage since infertility cannot be passed from one generation to the next. This damage to the DNA is caused by oxidative stress.

Oxidative stress occurs because sperms produce reactive oxygen species or ROS (molecules or ions with oxygen atoms containing unpaired electrons) in their environment and sperms are extremely vulnerable to reactive oxygen. When this environment of reactive oxygen species is stressed by ultraviolet light or heat exposure there is a significant increase in cell and DNA damage; this is called oxidative stress. Since the sperm is essentially naked with respect to the female ovum (egg), which has a protective cytoplasm around it, the sperms are deficient in both antioxidant and DNA-repair systems to protect it from the ROS. Therefore, oxidative stress is the main cause of male infertility and DNA damage, basically DNA fragmentation in the sperms.

Eventually, the fragmented DNA with the deleted genes will caused the cell to mutate and the mutated cell will ultimately ends up in the embryo during an abnormal recombination of DNA. The Y-chromosome has a high probability of these aberrant recombinations occurring because it has a high frequency of repetitiveness in it genes. Insertions of genes and amplification of genes, more than one copy of a gene inserted sequentially, also is caused by fragmentation of DNA by oxidative stress. Since this mutation occurs before the first division of an embryo cell, the mutation will enter the initial stage of development and contribute to infertility and sickness, including cancer, in the offspring.

Currently scientists do not know what causes oxidative stress or DNA fragmentation that inhibit the sperms to function properly. But they do know that these events put pressure on the vulnerable Y-chromosome. In the long run, selection against these males with poor quality sperms that favor sex reversal or sterility will create strong pressure either to retain fertility genes, or for any fertile variant that replaces them. If this happen, could the males of the human race as we know them now be replaced by a new fertile variant of us or several independent variants with an alternative sex determining system? A new human race could evolve and would be completely different from us in many ways depending on the gene pool of the handful of variants in the new group.

In conclusion, sex probably will not be the same as we know it now in a few thousand years of evolution. A course men do not have nothing to worry about now if they are able to procreate, but on the other hand future generations of men with infertility problems may become extinct for the sake of the human population.

Join HubPages, where you can write about the things you know and love—and even earn money! Click on the link in my profile page to join.Its free.