In each human pregnancies, there is always ________ %  probability of foetus being a male or female child.

In each human pregnancy, there is always 50 % probability of foetus being a male or a female child. All the haploid gametes (ova) produced by the female have the sex chromosome X whereas in the male gametes (sperms) the sex chromosome could be either X or Y, hence, 50 per cent of sperms carry the X chromosome while the other 50 per cent carry the Y. After fusion of the male and female gametes the zygote would carry either XX or XY depending on whether the sperm carrying X or Y fertilised the ovum.