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M utations

M utations. 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

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M utations

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  1. Mutations

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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)

  7. 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) • Individuals with favourable genotype pass this trait on the next generation • Individuals without favourable genotype often die out before reproduction

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