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Mutations

Mutations. Any change in DNA sequence which is not immediately and properly repaired. If they occur in somatic cells then they are non-inheritable, if in gametes then can be passed on to offspring.

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Mutations

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  1. Mutations • Any change in DNA sequence which is not immediately and properly repaired. • If they occur in somatic cells then they are non-inheritable, if in gametes then can be passed on to offspring. • Can be due to mistakes in DNA replication (spontaneous) or caused by mutagenic agents e.g. UV light, ionising radiation, Xrays, chemicals, viruses

  2. May be harmful, beneficial or neutral. • Usually recessive in diploids, can pass through many generations with no further change. • Two main types: gene mutations (point) and chromosome mutations (block, number of chromosomes or sets of chromosomes)

  3. Point Mutations • These are single gene mutations. There is a change in the DNA sequence of one base. This affects the amino acid coded for and therefore the protein. There are 3 types of point mutation.

  4. Substitution: a base is swapped for another base, the code for the amino acid may be changed resulting in a non-functioning protein. E.g. sickle cell anaemia. • Insertion: an extra base is added resulting in a frame shift in the reading of the code making a new sequence of amino acids. • Deletion: a base is removed resulting in a frame shift in the reading of the code making a new sequence of amino acids. E.g. cystic fibrosis.

  5. Tautomerism is where the wrong base pairing occurs which results in the amino acid sequence being misread.

  6. Block mutations • A change in structure of the chromosome. Groups of genes are affected and often occurs during crossing over or due to mutagens. Four types:

  7. Deletion: loss of a section of chromosome • Inversion: part of a chromosome turned around. • Translocation: part of one chromosome breaks off and is joined to another chromosome. • Duplication: part of a chromosome is copied and added to the chromosome.

  8. A bird flys thru the trees • A flys thru the trees • A drib flys through the trees • A flys thru bird the trees • A bird bird flys thru the trees

  9. Chromosome numbers • Aneuploidy: loss or gain of whole chromosomes • Polyploidy: loss or gain of sets of chromosomes. • All cause diseases with multiple effects which are called syndromes.

  10. Aneuploidy • Normally a human has pairs of homologous chromosomes (disomy). • Aneuploidy is where one pair of chromosomes either has monosomy (only 1 chromosome) or trisomy (three chromosomes). • Can occur in autosomes (nonsex chromosomes) e.g. downs, patau, edward syndrome

  11. Can occur in sex chromosomes e.g. Klinefelter (XXY) or Turner (XO) syndrome.

  12. Polyploidy • 3+ complete sets of chromosomes, common in plants and rare in humans (spontaneously aborts). • Autopolyploidy – within a single species • Allopolyploidy – within hybrid

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