Presentation on theme: "Mutatio ns. Variations which do not resemble either parent and have not occurred in family history. Do not have any known cause. Not necessarily harmful."— Presentation transcript:
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) o Individuals with favourable genotype pass this trait on the next generation o Individuals without favourable genotype often die out before reproduction
Your consent to our cookies if you continue to use this website.