SEX DETERMINATION

Genetic traits are determined by genes located on the chromosomes. The sex of an organism is a genetic trait which like other traits is transmitted from parent to offspring during sexual reproduction.

In all organisms with sexual reproduction there is a pair of chromosomes designated as X and Y chromosomes. In this instance, the entire chromosome, rather than the gene, controls the sex of the individual. Every normal female carries the pair XX and every normal male carries the pair XY.

Because of reduction division (meiosis) which takes place at gamete formation (Gametogenesis), the number of chromosomes is halved so that each mature gamete receives 23 chromosomes, distributed as follows:

 

We have to bear in mind that a normal human has 46 chromosomes (23 pairs) and reduction division at gamete formation brings the number down to 23.

The sex of the individual is determined by the sex chromosomes, X and Y. Fertilization of an ovum by a sperm containing an X chromosome results in the development of a female child, while a male child develops if the sperm fertilizing the ovum contains a Y chromosome. We can therefore correctly say that femaleness is determined by the X chromosomes while maleness is determined by the Y chromosome.

Boys inherit X chromosome from their father and Y chromosome from their mother while girls inherit X chromosome from their mother and X from their father.

The X and Y chromosomes have equal chances of fertilizing the ovum. Theoretically, this should result in an equal distribution between male and female births in the population as a whole.

Clinical records have shown that there is a slight tendency in favour of male births. An explanation of this is the greater motility of sperm carrying the Y chromosomes over that carrying the X chromosome.

 

Ignorance of these facts about sex determination has often placed severe strain on many marriages as the blame for the “wrong sex” often goes to the wife especially if she continuously delivers baby girls. Knowledge about sex determination is of great importance especially to young couples and it is hoped that modern advances in biochemistry and genetics will be of immense value in helping couples to select the sex of their children rather than to abandon one’s fate to nature.

Knowing the high motility of the sperms carrying the Y-chromosome, it may be interesting to investigate the effects of introduction of different media into the uterus of a female, or of continuously altering the pH values of the internal environment of a woman on successive deliveries. Does the frequency of male deliveries remain the same or is the balance tilted as a result of such introductions? These are some problems for the young biologists to attempt to answer.