150 red beads and 50 blue beads
Four large plastic beakers
Labels or marker pen
Blindfold
Getting started
- Males have one X and one Y chromosome in each of their body cells. Half their sperm have a Y chromosome and half have an X chromosome.Females have two X chromosomes.The red beads represent X chromosomes.The blue beads represent Y chromosomes.
- A set of100 red beads represent 50 females. A set of50 blue beads and 50 red beads represent 50 males.
Investigating
1Work in groups of three. Collect your equipment.
2Place100 red beads into a beaker. This represents the females in the population. Label the beaker ‘female parents’.
3Place 50 blue beads and 50 red beads into another beaker. This represents the males in the population. Label this beaker ‘male parents’. Label one of the remaining beakers ‘girls’, and the other ‘boys’.
4Shake the beakers containing beads.
5While wearing a blindfold, or without looking, pull out one bead from the female parent beaker and one from the male parent beaker.
6Hand them to your partner, who puts them into the jar labelled girls if they are both red, and the jar labelled boys if one is red and one is blue. The third person in your group keeps a tally of how many pairs of beads are in each jar.
7Continue selecting beads until your teacher asks you to stop.
Asking questions
AHow well does this model indicate the ratio of males to female in a small population?
BCould you improve the model if you used more beads and, if so, why?
Extension
Research one or more of the following topics:
AAndrogeninsensitivity syndrome
BIntersex (hermaphroditism) in humans
CKlinefelter syndrome
DTurner syndrome
EPolycystic ovary syndrome
FAnimals that can change their sex, for example oysters or chickens
GAnimals where sex of offspring is determined by temperature of incubation,for example turtles.
You will be asked to present a short summary to others in the class.