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Mutations and genetic variation

Mutations and genetic variation. Learning outcomes: Causes of mutations Effects of mutations Type of mutations. Keywords. Gametic mutation – permanent change to DNA of gametes, inherited mutation

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Mutations and genetic variation

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  1. Mutations and genetic variation Learning outcomes: Causes of mutations Effects of mutations Type of mutations

  2. Keywords • Gametic mutation – permanent change to DNA of gametes, inherited mutation • Somatic mutation – permanent change to DNA of normal body cells, affects person during their lifetime but not passed on. • Gene mutations – Mutations that affect one gene arise from point mutations – a change in the nucleotides on a DNA strand.

  3. Keywords continued • Chromosome mutation – occur during meiosis and result in whole sections of the chromosome being changed. • Aneuploidy – having an extra or missing chromosome due to non-disjunction during meiosis. • Polyploidy – having more than 2n chromosomes in each cell, usually only occurs in plants.

  4. What causes mutations? • http://www.youtube.com/watch?v=zcaeSKiZ37Y • http://www.youtube.com/watch?v=JLrMS_zs1kE

  5. What causes mutation • Mutations are spontaneous • Increases in the number of mutations are caused by environmental factors (mutagens) • UV light • X-rays • Benzene, formaldehyde, carbon tetrachloride

  6. Gametic and somatic mutations • Gametic – testis of males, ovaries of females, inherited • Somatic – in normal body cells occuring beyond zygote formation, not inherited but may effect the person during their lifetime. Chimaeras

  7. Mutagens and their effects • Ionising radiation – Nuc radiation, xrays, gamma rays (e.g. medical treatment) associated with development of cancers (e.g. leukaemia, thyroid cancer and skin cancer)

  8. Mutagens and their effects • Viruses and microorganisms – integrate into human chromosome, upset genes and can trigger cancer

  9. Mutagens and their effects • Environmental poisons – Organic solvents such as formaldehyde, tobacco, coal tars, benzene, asbestos, some dyes

  10. Mutagens and their effects • Alcohol and diet – High alcohol intake increase the risk of some cancers. Diet high in fat and those containing burned or highly preserved meat

  11. The effect of mutations • Not all are harmful • For some it can be a survival advantage • Most common among bacteria and viruses but also seen in insects • If no selective pressure against it, a mutation may remain in gene pool.

  12. Harmful mutations • Cystic fibrosis and sickle cell anaemia • Disfunctional proteins • Albinism – caused by mutation in gene of enzyme pathway of melanin

  13. Beneficial mutations • Bacteria – antibiotic resistance through mutation, transfer between bacterial species • Superbugs such as MRSA have arisen this way • RNA viruses – such as HIV – mutates it’s protein coat so that the host human is unable to make antibodies quick enough against it

  14. Neutral mutations • Neither harmful or beneficial to the organism but may be important in an evolutionary sense • Silent mutations • Virtually impossible to detect because no observable effect

  15. Normal red blood cell “Sickle” cell SOME MUTATION EXAMPLES

  16. BENEFIT Most mutations are harmful. Beneficial ones more common with short generation times. Many may be silent – not observed – and may only be selected for or against at a later date. Neutral mutations make no change at all, due to Degeneracy Example: DNA mRNA Amino acids Mutant DNA mRNA

  17. GENE MUTATIONS Three types : substitution, deletion, insertion Mutations that affect one gene arise from point mutations – a change in the nucleotides on a DNA strand. Normal DNA Normal polypeptide Mutant DNA mRNA Mutated DNA creates a STOPcodon which prematurely ends synthesis of the polypeptide chain e.g. Sickle cell anaemia

  18. Insertion Deletion Causes a frame shift – it stuffs up the whole rest of the sequence. Mutation: Insertion of C Original DNA Normal polypeptide Large scale frame shift results in a new amino acid sequence. The resulting protein is unlikely to have any biological activity. Mutant DNA mRNA Amino acids Page 144

  19. CHROMOSOME MUTATIONS These can only occur during meiosis. a.k.a. Block mutations. Inversion: Deletion: Examples: Cri-Du-Chat, Prader-Willi Examples: On chromosome 2 – unviable offspring

  20. Translocation: A section of one chromosome is lost to another one Duplication: A section of one chromosome is lost to its Homologue Chromosomes 9 and 22 – chronic leukaemia

  21. WHOLE CHROMOSOME MUTATIONS Normal (Euploid) humans have chromosomes (2 exact sets). Aneuploidy is the term for having 1 or more missing or extra. Monosomy = only one of a pair Polysomy = more than 2 of a pair, e.g. Trisomy = 3 homologues. This normally results from non-disjunction during meiosis. 46 Somatic cell Some examples: Trisomy chromosome 21 (Down’s) Monosomy sex chromosome (XO = Turner’s) Trisomy sex chromosome (XXY = Klinefelters) Gametes

  22. POLYPLOIDY n = haploid (gametes) 2n = diploid (normal individual) 3n or more = polyploidy Usually only in plants. Allopolyploidy – from a cross between 2 species. Hybrids, being a recombination of 2 lines, often show increased hybrid vigour. Autopolyploidy – from the same species.

  23. Autopolyploidy Allopolyploidy Page 159-160, Look at 161/2

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