The human body contains billions of cells, and each one of those cells contains 46 chromosomes. All except your sex cells.

Your sex cells are unique. Unlike every other cell in your body they only contain half the amount of chromosomal DNA.

Fertilisation

The sperm cell contains exactly half the amount of chromosomes of the individual, as does the egg.

When they meet, they create a cell with 46 chromosomes. Exactly half from each parent.

These sex cells and called Gametes.

When the fuse together they create a zygote.  

Even though the male can make millions of gametes, no two are the same.

This is because of how cells replicate and divide to form gametes. The process is called, Meiosis.

This causes genetic variation, which is extremely important in life.

These gametes are produced in the testes for men, and ovaries for women.

As we said before, your genetics are exactly 50% mum and 50% dad, however you may notice that your mother has brown eyes, while your dad has blue eyes.

We know humans have 46 chromosomes. On these chromosomes are genes. These genes code for proteins, which determine your appearance.

For example, lets say there’s one gene which codes for eye colour, and that gene is located on chromosome 3. Your mother may have the gene for brown eyes, while your dad has the gene for blue eyes. This variation is called an allele. An allele is a variation of a gene.

We know that in females there are two X chromosomes, while in men there is an X and a Y.

This means, that your mother can only give you of her X chromosomes, while your father can give you either his X or Y.