The Y chromosome carries characteristics of masculinity, while the X chromosome carries those of femininity. In the mother's egg, there is only the X chromosome, which determines female characteristics. In the semen from the father, there are sperms that includes either X or Y chromosomes. Therefore, the sex of the baby depends on whether the sperm fertilising the egg contains an X or Y chromosome. In other words, as stated in the verse, the factor determining the sex of the baby is the semen, which comes from the father. This knowledge, which could not have been known at the time when the Qur'an was revealed, is evidence to the fact that the Qur'an is the word of God.

Until fairly recently, it was thought that a baby's sex was determined by the mother's cells. Or at least, it was believed that the sex was determined by the male and female cells together. But we are given different information in the Qur'an, where it is stated that masculinity or femininity is created out of "a drop of sperm which has been ejected".

"He has created both sexes, male and female from a drop of semen which has been ejected." (The Qur'an, 53:45-46)

The developing disciplines of genetics and molecular biology have scientifically validated the accuracy of this information given by the Qur'an. It is now understood that sex is determined by the sperm cells from the male, and that the female has no role in this process.

Chromosomes are the main elements in determining sex. Two of the 46 chromosomes that determine the structure of a human being are identified as the sex chromosomes. These two chromosomes are called "XY" in males, and "XX" in females, because the shapes of the chromosomes resemble these letters. The Y chromosome carries the genes that code for masculinity, while the X chromosome carries the genes that code for femininity.

The formation of a new human being begins with the cross combination of one of these chromosomes, which exist in males and females in pairs. In females, both components of the sex cell, which divides into two during ovulation, carry X chromosomes. The sex cell of a male, on the other hand, produces two different kinds of sperm, one that contains X chromosomes and the other Y chromosomes. If an X chromosome from the female unites with a sperm that contains an X chromosome, then the baby is female. If it unites with the sperm that contains a Y chromosome, the baby is male.

In other words, a baby's sex is determined by which chromosome from the male unites with the female's ovum.

None of this was known until the discovery of genetics in the 20th century. Indeed, in many cultures, it was believed that a baby's sex was determined by the female's body. That was why women were blamed when they gave birth to girls.

Thirteen centuries before human genes were discovered, however, the Qur'an revealed information that denies this superstition, and referred to the origin of sex lying not with women, but with the semen coming from men.