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Bottlenecks and founder effects

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The molecular basis of variation and inheritance: key words

  • The human genome varies by about 0.5% between individuals. This variation arises from single nucleotide polymorphisms and from insertions, deletions, inversions and duplications of longer sequences.
  • Patterns of sequence variation between populations provide information about human origins and the selective pressures that humans have experienced.
  • Only a small proportion of sequence variation causes detectable phenotypic change.
  • Although monogenic diseases such as cystic fibrosis tend to be rare, several mechanisms account for the fact that selection has not altogether eliminated the deleterious alleles from the population: recurrent mutation, delayed onset after reproductive age, and heterozygote advantage.
  • Genetic susceptibility to common diseases such as type 2 diabetes probably arises from the combined effects of numerous alleles contributing to risk, each having small effects, coupled with environmental and developmental factors.
  • Not all inheritance is genetic. Disease risk can be transmitted by cultural or behavioural factors, and there is increasing evidence for trans-generational persistence of epigenetic modifications of DNA and gene expression.


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