Human Characteristics (B1)

Sexual reproduction causes variation

Gametes contain only 23 chromosomes.They contain 1 of each chromosome type but the way they get split up is random. 

Chromosomes swap pieces of DNA with each other when they pair u during cell division. This increases variation.

Fertilisation:

Every egg and sperm is genentically unique.

The joining of an egg with one of millions of sperm is random.

Sex Chromosomes:

Women - **

Men - XY

The ratio of baby girls to baby…