how a child gets one copy of each gene from his/her mother and another copy of each gene from his/her father.

Explanation:

One copy is from the mother, via the egg and the other is from the father, via the sperm. The sperm and egg each contain 23 chromosomes each and when the sperm fertilizes the egg, two copies of each chromosome are there, so therefore, two copies of each gene. This causes an embryo to form, which then develops into a child.

The basic answer is sexual reproduction

Explanation:

There is a sperm and an egg, each one contains 23 chromosomes. When the sperm fertilizes the egg two copies of each chromosome are present therefore two copies of each gene (mother and father) and so ta-da! You now have an embryo formed.

layer 3 is younger than layer 6.