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Two parents are needed in sexual reproduction. During this process the nucleus of a male gamete fuses with the nucleus of a female gamete, producing a new cell called a zygote .

In human beings, each gamete contains 23 chromosomes, half the number found in the other cells of the body. When the male and female gametes fuse, they become a zygote, which in turn becomes a new embryo containing the full 46 chromosomes – half from the father and half from the mother.

This fusion of gametes is called fertilisation.

Gametes are formed by a type of cell division called meiosis. In animals the gametes are sperm and eggs.

In flowering plants the gametes are pollen and eggs.

In meiosis:

• copies of the genetic information are made
• the cell divides twice to form four gametes, each with a single set of chromosomes known as haploid cells
• all gametes are genetically different from each other, they show variation

Comparing mitosis and meiosis