Females have XX chromosomes, that is, they can only give one X chromosome. But since males have XY chromosomes then men can either give the X or the Y chromosome.
This means that it is actually the males who determine the sex of the baby (by giving either the X or the Y chromosome). This was known recently however this was portrayed in the Quran 1400 years before it was discovered.
[Quran 53:45-46] And He (Allah) creates pairs, male and female, from sperm emitted.
"Nutfa نُطْفَةٍ" means sperm. The Quran says that it is the sperm that determines whether the baby is male or female. But since sperm only comes from males then this means that it is the males who determine the sex of the baby.
The verse number 46 is the same number of chromosomes humans have (23 pairs = 46).
But each of those million sperms has a different combination of chromosomes. And they are all competing to a single ovule (one set of chromosomes). So the difference in chromosomes are only in sperms (not in the ovule). This was known recently, however this was portrayed in the Quran 1400 years become it was discovered.
[Quran 76:2] We created man from a mixed sperm, to test him; and We made him hearing and seeing.
"Amshaje أَمْشَاجٍ" means mixed or not unique. Today we know that chromosomes of the sperm are not unique.
How could an illiterate man who live 1400 years ago have known that sperms determine the sex of the baby? How could he have known that sperms are not unique?
(While today's scientists have confirmed that animals inherit their colors and stripes from their parents (through DNA), the Christian Bible says something else: In Genesis 30:37-42, the Bible explains how baby goats get their streaked colors: If their parents were mating AND LOOKING at upright rods then the baby goats will have stripes; while if their parents were mating BUT NOT LOOKING at upright rods then the baby goats will not have stripes!)