Fortune teller

In the delivery room, the happiest moment is that the mother gave birth to the baby smoothly, and the mother and child are safe. It is time for the family to judge the newborn baby.

Although the newborn baby's face is red, her skin is wrinkled, her eyes are hard to open and her hair is missing, it looks the same to outsiders. However, in the eyes of the baby's family, it is a darling.

This morning, the maternal brother gave birth to a little boy. Little brother's mother is in the ward, holding her grandson, and she can't see enough.

"Mom, look, this child doesn't look like me or his father." Xiao Ge said at a side.

"Well, the child is like his uncle. Look at these eyebrows. How similar. "

"No wonder the old saying" My nephew is like an uncle "really makes sense."

Just as the mother and daughter were talking, Dr. Bai went into the ward to make rounds. Dr. Bai listened to them and said, "It's actually very simple. It is the role played by atavism. "

Atavism? Little brother and little brother mother froze.

"Yes," Dr. Bai explained, "the so-called atavism refers to a family in it runs in the family. The first and third generations have similar phenotypes, but the second generation does not. It is the result of heredity, epigenetic inheritance and quantitative inheritance. "

"But what does this atavism have to do with his nephew?" Little brother listened to Dr. Bai's words, but he was even more confused.

Dr. Bai said, "Why does my nephew look like an uncle? Because mom and uncle have the same X chromosome from grandma, and mom has another X chromosome from grandpa. At this time, one chromosome is often a dominant gene and the other chromosome is a recessive gene. The Y chromosome in nephew comes from his father, and the X chromosome from his mother has similar sexual characteristics with his uncle. When this chromosome is a dominant gene, nephews and uncles have many similarities. That is, we often say that nephews are like uncles. "