In human beings Sex determination is due to sex chromosomes. Therefore, it is a genetic mechanism. In biology, it is a system which decides the sexual characteristics of an organism or offspring. Genes which are inherited from the parents determine whether a progeny will be a boy or a girl. Genes for every characters is linearly arranged on chromosomes. Which also include the genes for sexual characters.
Usually, characters related to the reproductive system are called sexual characters and the ones that are not called are vegetative characters. The chromosomes that have genes for sexual disposition are called sex chromosomes, on the other hand those that have genes for the vegetative characters are called autonomies.
A sex chromosome which carries the genes for male characters is called Y chromosome and one that carries the genes for female characters is called X chromosome.
So we have in total 46 chromosomes. Half of them always come from the mother and the rest is inherited from the father. Out of 46 chromosomes, there are 44 autonomies and 2 are sex chromosomes. The sex chromosomes can be different they are not always a perfect pair.
In females there are 44 autonomies with two X chromosomes, in males there are 44 autonomies, one X chromosome and one Y chromosome. Then the chromosomes exists in woman are 44 + XX, whereas the chromosomes in man are of 44 + XY. Let’s look into the inheritance specimen of X and Y chromosomes.
Through the course of gamete formation, the normal diploid chromosome number is halved which is called the haploid condition. Every eggs of a female contain 22 + X chromosomes. Coming to the male, he produces two types of sperms—one type have the 22 + X composition and the other type bears 22 + Y. Therefore, in each and every 100 sperms, 50 of them have Y chromosomes and 50 have X chromosomes.
X-Y System of Sex Determination in Man
Any one of the two types of sperms can inseminate the egg. If a sperm having Y component fertilizes the egg, the zygote has the 44 + XY constitution, then the resulting embryo grows to be a boy but when an X-bearing sperm manure the egg, the out coming zygote has the 44 + XX composition. This embryo develops into a girl. All the children inherit one X chromosome from their mother.
Thus, sex is always determined by the other sex chromosome which they always inherit from the father. The one who inherits the X chromosomeof the father is definitely a girl, while one who inherits the Y chromosome of the father is without a doubt a boy.