Which parent determines the sex of a child?

The father provides an X or Y chromosome; the mother always provides an X chromosome. Therefore, the sex of the child is determined by the chromosome of the individual sperm that fertilizes the egg.

Male offspring carry XY chromosomes; female offspring carry XX chromosomes.

Information from another contributor
  • the father deposits the semen containing sperms in the vagina of mother. ideally the X and the Y sperms are in same number (this is rarely the case).

  • the germ cell in father's testicle initially divides into 2 cells. one of which is Y sperm responsible for male child. second one is X sperm responsible for female child. These cells then each divide in 2 these 2 cells further divide in 2 each producing 4 of one kind. this process goes on and on to produce 50 millions to 150 millions sperms in the semen. Half of them are Y sperms and Other half are X sperms.

  • If the X sperm unite with female egg then a female child is born.

  • If Y sperm unite with female egg then a male child is produced.

  • As same number of Y and X sperms are deposited in the vagina; which type of sperm ultimately will unite with female egg depends on the conditions of female reproductive system. Whether the condition is favorable for the rapid and safe movement of X sperms or the Y sperms.

  • The Y sperms are very delicate and are easily get destroyed by acidic and toxic environment of vagina. Thus if the vagina is very acidic most of the Y sperms are destroyed the rest may get immobile and not fit to swim in the cervical canal.

  • The X sperms are stronger and can withstand the acidity and toxicity better.

  • Thus if the medium of the reproductive organ mainly vagina, cervix, uterus and fallopian tubes is not favorable then the Y sperms get destroyed or immobile and the surviving X sperms swim in to unite with X egg of the woman to produce female child. This is why failure of family planning method like condom, spermicides, jelly, or withdrawal mostly results in female child. Similarly women having vaginitis, cervicitis, leucorhea, candida infection, cervical erosion almost always produce female children.