How is sex determined in human beings ?

Explanation

A. Sex determination in Humans : It has already been mentioned that the sex determining mechanism in case of humans is XX-XY type. Out of 23 pairs of chromosomes present,22 pairs are exactly same in both males and females, these are the autosomes. A pair of X- chromosomes is present in the female, where as the presence of an X and Y - chromosome are determinant of the male characteristic. During spermatogenesis among males, two types of gametes are produced. 50 percent of the total sperm produced carry the X,- chromosome and the rest 50 percent has y - chromosome besides the autosomes.. Females, howeverproduce only one type of ovum with an X-chromosome. There is an equal probability of fertilisation of the ovum by the sperm carrying either X or Y chromosome. In case the ovum is fertilised by a sperm carrying X-chromosome, the zygote develops into a female and the fertilisation of ovum with Y - chromosome carrying sperm results into a male offspring. Thus, it is evident that it is the genetic makeup of the sperm that determines the sex of the child: it is also evident that’in each pregnancy there is always 50 percent probability of either a male or a female child