S13) DNA Mutations Flashcards

1
Q

What is a mutation?

A

A mutation is a change in a DNA sequence

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2
Q

Describe 4 ways in which mutations can arise

A
  • DNA replication errors during cell division (mitosis and meiosis)
  • Exposure to ionising radiation (mutagens)
  • Exposure to chemicals (chemical mutagens)
  • Infection by viruses
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3
Q

Distinguish between a somatic mutation and a germ line mutation

A
  • A germ line mutation occurs in the eggs/sperm, affecting all cells in the body and can be passed on to offspring
  • A somatic mutation occurs in a somatic cell and is not passed on to offspring
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4
Q

Why are RNA translation errors not as severe as errors in the genome?

A
  • RNA errors are unlikely to occur repeatedly in the same place
  • RNAs are quickly degraded
  • RNAs are not inherited molecules passed down to offspring
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5
Q

Mitochondrial DNA is also prone to somatic mutations, which are not inherited.

Why are mitochondrial somatic mutations often severe?

A
  • mtDNA has a limited ability to repair itself so mutations accumulate over time
  • mutations of mtDNA are associated with forms of cancer and an increased risk of age-related disorders e.g. heart disease, Alzheimer’s Parkinson’s
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6
Q

With reference of autosomal dominant and recessive disorders respectively, outline the possibility of spontaneous mutations

A
  • In an autosomal dominant disorder, e.g achondroplasia, if a parent is not affected then a spontaneous mutation has occurred in the affected child
  • In an autosomal recessive disorder, e.g cystic fibrosis, if no heterozygous/homozygous parents, then a spontaneous mutation of the same gene on both chromosomes has occurred (incredibly unlikly)
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7
Q

Classify germ line mutations in terms of macro and micro mutations.

A
  • Micromutations (gene): substitution, insertion, deletion
  • Macromutations (chromosome):

I. Structural - deletion, duplication, inversion, translocation

II. Numerical - non-disjunction

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8
Q

Explain why the mutation rate in male gametes is approx. 5x higher than in female gametes

A
  • The number of germline divisions in spermatogenesis vastly exceeds that in oogenesis
  • Spermatogonial germ cells are continually active in adult men and the male mutation rate increases with age
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9
Q

Why do male and female gametocyte mutations increase with age?

A
  • Spermatozoa are continually made
  • Older spermatagonia have been exposed to mutagens/radiation for a longer time
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10
Q

What do you think are the possible outcomes if a very early embryo was exposed to radiation?

A
  • Death/aborted
  • Teratogenesis
  • Cancer when born
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11
Q

Which 4 features enable a germ cell mutation to be inheritable?

A
  • Not lethal to the gamete
  • Does not impair gamete function
  • Not lethal at fertilisation
  • Allows for the production of a viable adult with normal reproductive capacity
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12
Q

In terms of their respective effects, describe the general trends observed in recessive and dominant mutations

A
  • In general, recessive mutations cause loss of function and often affect biochemical pathways
  • In general, dominant mutations cause increased function and often cause structural abnormalities
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13
Q

In terms of mutations in proteins, explain why there is an increased incidence of recessive mutations

A

A given mutation is much more likely to be deactivating/inactivating than introduce a new function because there are far more ways to deactivate/ inactivate a protein

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14
Q

In terms of the trends seen in protein mutations, account for the varying effects amongst recessive and dominant mutations

A
  • Reccesive mutation: if heterozygous, failure of one allele to produce a protein can be compensated for by the normal allele, thus masks the effect
  • Dominant mutation: if heterozygous, overproduction by a single allele cannot be ‘compensated for’ by the other normal allele, thus produces an effect
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15
Q

How do somatic mutations arise?

A
  • Mutagens
  • Radiation
  • Viruses
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