The next slide shows the key elements for this topic in the

Gateway Biology for OCR Biology

Genetic variation

Caused by

Alleles

are

Different versions of the cells DNA code

Gametes

are

Male and female sex cells

Contain only 23 chromosomes and all are

different

1. Gamete formation – splitting

of the male and female cell in gamete

formation leads to random different sex

cells.

2. Fertilisation – when gametes combine during

fertilisation the 23 chromosomes from

the male and female randomly form the 46 chromosomes of the

new baby

3.Mutations – spontaneous

incorrect division of DNA OR

environmental factors such as

aggressive chemical attack, UV, X rays or gamma rays on cells