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But if you're looking for the effects of a recessive gene, you'll need a rat that is homozygous recessive, or who carries two identical copies of the recessive gene. Wild rats are typically brown, but most lab rats are albino, meaning they don't have any pigment in their fur or eyes. The albinism gene lives at a certain locus, or place on the DNA strand.
People with albinism may have trouble with their vision, but are otherwise fairly healthy.
Recessive alleles are ones that only show their traits if two copies of that allele are present.
So it's good to have one copy, but bad to have two.
Albinism can occur in people, too - not just in rats.
Free 5-day trial Most plants and most animals - including you, if you're human - have two copies of each of their genes.