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Page 1: © Boardworks Ltd 20091 of 3. 2 of 3© Boardworks Ltd 2009 What are sex chromosomes? Humans cells contain one pair of sex chromosomes, which control gender

© Boardworks Ltd 20091 of 3

Page 2: © Boardworks Ltd 20091 of 3. 2 of 3© Boardworks Ltd 2009 What are sex chromosomes? Humans cells contain one pair of sex chromosomes, which control gender

2 of 3 © Boardworks Ltd 2009

What are sex chromosomes?

Humans cells contain one pair of sex chromosomes, which control gender.

Males have one X andone Y chromosome (XY).

Y chromosomes are very small and contain 78 genes, whereasX chromosomes are larger and contain 900–1,200 genes.

Because females can only produce X gametes, it is the sperm that determine the sex of the offspring at fertilization.

X chromosome

Y chromosome

Females have two X chromosomes (XX).

Page 3: © Boardworks Ltd 20091 of 3. 2 of 3© Boardworks Ltd 2009 What are sex chromosomes? Humans cells contain one pair of sex chromosomes, which control gender

3 of 3 © Boardworks Ltd 2009

Boy or girl?