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An allele is an alternative version of a gene.
still at the same locus on the chromosome
codes for the same polypeptide
alteration to the DNA base sequence may alter the proteins structure
Mutations with neutral effects
if a gene is altered by a change to its base sequence, it becomes an allele of the gene
no change to the organism may occur if:
The mutation is in a non-coding region of the DNA
The mutation is a silent mutation
if the mutation causes a change to the structure of the protein, which gives a different
characteristic, but the changed characteristic gives no particular advantage or disadvantage to the
organism, the mutation is said to be NEUTRAL
Mutations with harmful or beneficial effects
early humans in Africa had dark skin
the pigment melanin protected their skin from the harmful effects of UV light
they were still able to synthesise vitamin D from the action of intense sunlight on their skin
any humans with mutations to some of the genes determining skin colour, producing paler kin
old have burned and suffered from skin cancer
as humans migrated to more temperate climates, the sunlight was not intense enough to cause
enough Vitamin D to be made by those with dark skin
humans with mutations producing paler skin would have had an advantage over those with
dark skin, as they could synthesise more vitamin D


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