Mutations


  • Mutations increase genetic diversity of the population they occur in and are the only source of new alleles for a species.


  •  Migration from one population to another results in mutated alleles entering the gene pool of other populations.


  • The alleles of a gene that are in the greatest numbers in a gene pool of a natural population are called 'wild-type' alleles. These produce the correct amount of functional proteins. 


  • Mutated alleles are less common in natural populations because they can produce smaller amounts of protein or proteins that do not function as well. 


  • However in selectively bred populations, people breed animals with mutated phenotype eg yellow feathered parrots created by a mutated allele are bred more than the normal (wild-type) green feathered parrot.


  • Often more than one mutation occurs in a gene, resulting in many alleles for that gene (eg coat colour gene in rabbits, dominant C allele produces dark grey while recessive c allele produces albino (white) colour. Two different mutations of coat colour produces light grey (cch) or himalayan pattern (ch). The order of dominance for the alleles are C - cch - ch - c. The mutated allele ch produces an enzyme that only functions in low temperatures so dark fur occur in cool areas of the body like nose, ear, foot and tail.


  • Harmful mutations - Some mutations cause genetic disorders eg cystic fibrosis caused by a mutation in a gene on chromosome number 7. The normal allele produces a protein that transports chloride ions actoss plasma membranes. About 70% of mutations in this gene results in 3 bases (CTT) being missed and the resulting protein can't transport chloride ions in a normal way, which leads to mucus build up.


  • Helpful mutations - Some mutations are helpful that give a better chance of survival. Individuals survive to reproduce and pass on the beneficial mutation. This results in more individuals in population  carrying the mutated allele, so the alleles frequency in the gene pool increases and the other allele frequency for the gene decreases.
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