Inheritance of Sex Flashcards

All 6 cards in this deck

Which sex chromosomes do human females and males have?

Females are XX; males are XY.

What are the steps to use a genetic diagram to show how sex is determined in humans?

e.g. XX mother $\times$ XY father

1. Write the parents' gametes: mother X and X; father X and Y.
2. Combine them in the Punnett square: XX, XX, XY, XY.
3. Read the outcome: 2 female : 2 male, i.e. a 50% chance of each.

Which parent determines the sex of a child, and why?

The father — his sperm carry either an X or a Y chromosome, while all the mother's eggs carry an X.

What is the probability that a human baby is male?

50% (1 in 2) — a 1 : 1 ratio of males to females.

True or false? Every human egg cell contains an X chromosome.

True. The mother is XX, so all her eggs carry an X chromosome.

True or false? A couple who already have three sons are more likely to have a daughter next.

False. Each fertilisation is independent, so the chance is still 50% male and 50% female.