Sexual Reproduction

sexual reproduction is the joining (fusion) of male and females gametes. The mixture of the genetic information from two parents leads to variety in the offspring

There are special cells that our bodies produce that only have 23 chromosomes. They are called gametes. The male gamete is the sperm cell. The female gamete is the egg cell.

When two gametes fuse together they form a new cell which has 46 chromosomes. This new cell my then divide and form a new individual which has a mixture of genes from each parent.

Sperm and egg cells form, in the testis and ovaries of the parents, when a normal cell splits, a process call meiosis.

Of the 23 pairs of chromosomes any sperm cell may get either chromosome from each pair. The chances of any two sperm cells having exactly the same chromosomes is therefore very small, the same as rolling a dice 23 times and landing on heads every time, about 1 in 8 and1/2 million. (Saying that the average male produces several hundred million sperm every day.)

Because successful sperm (and eggs) have different chromosomes the offspring will show variation.

Some will be taller or smaller. Some will be cleverer. Some will be faster or stronger. Some will have curly hair and other straight etc.

This of course does not apply to identical twins. In this case the egg splits into two embryos after fertilisation so the offspring have exactly the same chromosomes.