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There are pairs of chromosomes in the nucleus of a body cell.

The chromosomes in a pair carry the same genes in the same places.

But there are different versions of the same gene.

Alleles: different versions of the same gene.

For example, the gene for eye colour has an allele for blue eye colour and an allele for brown eye colour.

For any gene, a person may have the same two alleles or two different ones. [1]

Dominant alleles

A dominant allele is always expressed, even if the individual only has one copy of it.

For example, the allele for brown eyes is dominant.

You only need one copy of it to have brown eyes.

Two copies will still give you brown eyes. [2]

Recessive alleles

A recessive allele is only expressed if the individual has two copies of recessive and does not have the dominant allele of that gene.

For example, the allele for blue eyes is recessive.

You need two copies of this allele to have blue eyes. [3]





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