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Mutations
•Variations which do not resemble either parent and have not occurred in family history. Do not have any known cause. Not necessarily harmful.
•Mutant: An organism which possesses a mutation
•Mutagens / Mutagenic agents: increase the rate by which mutations occur (do not necessarily cause defects)
-E.g mustard gas, formaldehyde, sulphur dioxide, some antibiotics, radiation (UV, X-ray, Cosmic), radioactive substances
•Mutations can be in two types of cell:•Somatic Mutations: Mutations in the body cells
-Individual is affected but generally not offspring (eg of exception: PKU)
•Germinal / Germline mutations: Mutations in the gametes / sex cells
-Individual is generally not affected but offspring usually are-Often naturally aborted
Two types:
1. Gene Mutations•Change in the sequence of nitrogen bases in a gene.•May:
-Alter protein being made-Have no effect-Not make protein at all
•E.g. Albinism, Duchenne Muscular dystrophy, Cystic fibrosis
2. Chromosomal Mutations•Change is all or part of chromosome (many genes)•May be:
-Deletions: loss of part of a chromosome-Duplications: section occurs twice (part breaks off and rejoins to wrong chromatid)-Inversions: breaks occur and piece rejoins but backwards-Translocations: addition of part of a chromosome (part breaks off and rejoins to wrong chromosome)-Non-disjunctions: chromosome pairs do not separate (also called aneuploidy)
•E.g. Down syndrome, Patau syndrome, Klinefelter’s syndrome, Cri du chat syndrome, Turner’s syndrome
New Variations and Survival•E.g Sickle cell anaemia:
-Inheritance of sickle cell anaemia results in death at birth-This should gradually reduce frequency of the allele until it disappears - not the case-Possible explanation could be that the rate of mutation (production of new sickling cells) equals the rate of loss due to infant death - also not the case (loss is 100x greater than mutations)
New Variations and Survival•E.g Sickle cell anaemia:
-Second explanation is that heterozygous (sickle cell trait) is a selectively advantageous mutation.-An example of natural selection (environment favours one genotype over another)
oIndividuals with favourable genotype pass this trait on the next generationoIndividuals without favourable genotype often die out before reproduction