Narrated Anas:
When 'Abdullah bin Salam heard the arrival of the Prophet at
Medina, he came to him and said,
"I am going to ask you about
three things which nobody knows except a prophet: ... Why does
a child resemble its father, and why does it resemble its maternal
uncle" Allah's Apostle said, "Gabriel
has just now told me of
their answers." 'Abdullah said, "He (i.e. Gabriel), from amongst
all the angels, is the enemy of the Jews." Allah's Apostle said,
"... As for the resemblance of the child to its parents: If a man
has sexual intercourse with his wife and gets discharge first, the
child will resemble the father, and if the woman gets discharge
first, the child will resemble her."
On that 'Abdullah bin Salam said, "I testify that you are the Apostle of Allah." ...
(Sahih Bukhari 4.546.
also Sahih Bukhari 5.275,
Sahih Bukhari 6.7)
Wow! What scientific knowledge!
The number of
Science tells us that the sex of a baby is determined by the
Y-chromosome of the father. A male has an XY pair of chromosomes
while a female has an XX pair (there are some extreme exceptions
like XXY, etc, but these are exceptions),
and a sperm cell carries either the X or the Y chromosome,
and the female egg carries the X chromosome. Thus,
during fertilization, either an X or a Y chromosome of the father
combines with an X chromosome of the mother, and the
chromosome type of the sperm determines the sex of the baby.