The Sex Chromosomes
The sex chromosomes carry genes that determine whether a person is male or female. They also carry genes that determine other traits.
Females: Two chromosomes, called X chromosomes.
Males: Two chromosomes, one is an X chromosome the other is a Y chromosome. The Y chromosome is much smaller than the X chromosome.
The punnett square below shows the combinations of offspring a couple may have:
The sex of an offspring all depends on which chromosome the male sperm cell is carrying when it fertilizes an egg. If the sperm cell is carrying an X chromosome then the offspring will be female. If the sperm cell is carrying a Y chromosome then the offspring will be male.