The father decides
The child's sex depends on the father's chromosome.
Boy or girl?
A mother is XX and a father is XY. Their child gets one sex chromosome from each parent.
Which parent's chromosome decides whether the child is a boy or a girl?
What this lesson covers
The idea
Every person inherits an X chromosome from the mother, so sex is decided by the father's contribution: an X from him gives a girl, a Y gives a boy, and half the offspring are boys and half girls.
Boy or girl?
A mother is XX and a father is XY. Their child gets one sex chromosome from each parent.
Which parent's chromosome decides whether the child is a boy or a girl?
- The father's
- The mother's
- Both equally
Pass on a chromosome
Choose what the father passes on.
Half and half
The mother has only X chromosomes to give, so every child gets an X from her. The father can pass on an X or a Y. So half the children are girls and half are boys.
Every child inherits an X from the mother, so the sex is decided by the father's contribution. An X from the father gives a girl, a Y gives a boy. Half the offspring are boys and half girls.
Notes
The mother passes on an X; the father's chromosome decides: X gives a girl, Y gives a boy, and half the offspring are boys and half girls.
Check yourself
Which sex chromosome does every child inherit from the mother?
A child who inherits a Y chromosome from the father will be…
What decides the sex of a child?
Half the children will be boys. Out of 200 children, how many will be boys?
Answer: 100
Half of 200 is 100.
- A Y chromosome. Women have a perfect pair, both called X, so they have no Y to pass on.
- Either an X or a Y. The mother has two X chromosomes, so every child inherits an X from her.
- An X chromosome — correct. Yes!
- a boy — correct. Yes!
- a girl. A child who inherits an X chromosome from the father will be a girl.
- a boy or a girl, depending on the mother. Every child inherits an X from the mother, so the mother does not decide the sex.
- What the child inherits from the mother. All children inherit an X from their mother, whether they are boys or girls.
- What the child inherits from the father — correct. Yes!
- The temperature at which the egg is kept. That is how sex is decided in a few reptiles. In human beings it is largely genetically determined.