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