In this Sahih Bukhari hadith, Muhammad explains why a child sometimes resembles its father & sometimes its mother!
Volume 4, Book 55, Number 546: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: What is the first portent of the Hour? What will be the first meal taken by the people of Paradise?
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 answersAbdullah said,"He (i.e. Gabriel), from amongst all the angels, is the enemy of the Jews." Allah's Apostle said, "The first portent of the Hour will be a fire that will bring together the people from the east to the west; the first meal of the people of Paradise will be Extra-lobe (caudate lobe) of fish-liver.
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."So now we know why a child resembles a particular parent!