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Mutations and Chromosomal Abnormalities

Mutations and Chromosomal Abnormalities. Higher Human Biology. Mutations. A mutation is a change in the structure or amount of an organisms genetic material When a change in genotype produces a change in phenotype, the individual is called a mutant. Gene Mutations.

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Mutations and Chromosomal Abnormalities

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  1. Mutations and Chromosomal Abnormalities Higher Human Biology

  2. Mutations • A mutation is a change in the structure or amount of an organisms genetic material • When a change in genotype produces a change in phenotype, the individual is called a mutant

  3. Gene Mutations • POINT MUTATIONS – substitution, inversion; bring about only a minor change (ie one different amino acid); sometimes the organism is affected only slightly or not at all • FRAMESHIFT MUTATIONS – insertion , deletion; leads to a large portion of the gene’s DNA to be misread; the protein produced differs from the normal protein by many amino acids and is usually disfunctional

  4. Substitution

  5. Inversion • Inversion of two or more nucleotides

  6. Insertion

  7. Insertion

  8. Deletion

  9. Chromosomal Abnormalities • During meiosis in humans unusual gametes can be formed which contain 22 or 24 chromosomes • These abnormal gametes are formed when a spindle fibre fails and one of the pair of homologous chromosomes fail to become separated • This is called non-disjunction

  10. Non-disjunction

  11. Down’s Syndrome • Due to non-disjunction of chromosome 21 • An extra copy of chromosome 21 is seen in the karyotype of someone with Down’s syndrome • The affected individual is characterised by mental retardation and distinctive physical features • Egg mother cells of older women tend to be more prone to non-disjunction at meiosis

  12. Down’s Syndrome Karyotype

  13. Non-disjunction of Sex Chromosomes • If human sex chromosomes are affected by non-disjunction during meiosis then unusual gametes are formed

  14. Turner’s Syndrome

  15. Turner’s Syndrome • Chromosome complement 2n = 44 + XO • Individuals are always female and short in stature • Their ovaries do not develop so they are infertile and fail to develop secondary sexual characteristics e.g. breast development and menstruation

  16. Klinefelter’s Syndrome

  17. Klinefelter’s Syndrome • Chromosome complement 2n = 44 + XXY • Individuals are always male and possess male sex organs • They are infertile since their testes only develop to half the normal size and fail to produce sperm • Testes produce low levels of testosterone so facial hair, deepening of voice are only weakly expressed

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