X and Y

The idea

Females have XX and males XY sex chromosomes; the mother always contributes an X, and the father contributes either an X, giving a female (XX), or a Y, giving a male (XY).

Girl or boy

Every baby is born as a girl or a boy.

What do you think decides this?

• The chromosomes the baby receives from its parents
• The colour of the room
• The month of the year

What does the father give?

The mother has XX and the father has XY. Choose what the father gives.

The father's gamete decides

The mother always gave an X. So the baby's sex depended on what the father gave: an X made XX, a female, and a Y made XY, a male.

Females have XX and males have XY sex chromosomes. The mother always contributes an X, and the father contributes either an X, giving a female (XX), or a Y, giving a male (XY).

Notes

Females XX, males XY. The mother always gives an X; the father gives an X (female XX) or a Y (male XY).

Check yourself

Which sex chromosomes do females have?

What does the mother always contribute to a baby?

The father contributes a Y chromosome. The baby will be…

Who determines the sex of the baby, since the mother always gives an X?

• XX — correct. Yes!
• XY. Males have XY.
• YY. Females have XX. Males have XY.
• A Y chromosome. The mother has XX, so she always contributes an X. A Y chromosome comes from the father.
• An X chromosome — correct. Yes!
• Either an X or a Y. The mother always contributes an X chromosome.
• female, XX. A female (XX) results when the father contributes an X.
• female, XY. Females have XX. XY is male.
• male, XY — correct. Yes!
• The father, by giving either an X or a Y — correct. Yes!
• The mother, by giving either an X or a Y. The mother always contributes an X. It is the father who contributes either an X or a Y.
• Neither parent. The baby's sex depends on whether the father contributes an X or a Y.