AQA AS Biology Unit 2 - Genetic Diversity

The third topic for Unit 2 AS BAQA Biology- Genetic diversity

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What is genetic diversity

  • The greater the number of different alleles that all members of a species posses the greater the genetic diversity of that species.
  • The greater the genetic diversity the more likely that a species will be able to adapt to some environmental change.
  • This is because it will have a wider range of alleles and therefore a wider range of characteristics.
  • There is therefore a greater probability that some individual will possess a characteristic to suits its new environmental conditions.
  • Genetic diversity is reduced when a species has fewer different alleles.
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Selective Breeding

(also known as artificial selection)

It involves identifying individuals with desired characterisitcs and using them to parent the next generation. Offspring that do not exhibit the desired characteristics are killed, or at least prevented from breeding, In this way alleles for unwanted characterisitcs are bred out of the population. The variety of alleles in the populations is deliberately restricted to a small number of desired alleles.

Ofver many generations, this will lead to a population all of which possess the desired qualities but which has reduced genetic diversity.

Selective breeding is commonly carried out in order to produce high-yielding breeds of domesticated animals and strains of plants.

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The Founder effect

The founder effect occurs when just a few individuals from a population colonise a new region. These individuals will carry with them only a small fraction of alleles of the populations as a while.

These alleles may not be representative of the larger population.

The new population that develops from the few colonisers will therefore show less genetic diversity than the population from which they came.

The founder effect is often seen when new volcanic islands rise out of the sea. The few individuals that colonise these barren islands give rise to apopilation that is genetically distincts from the populations they left behind, The new populations may in time develop separate species. As these species have fewer alleles they are less able to adapt ti changing conditions.

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Genetic bottlenecks

  • Populations of a species may from time to time suffer a dramatic drop in numbers. Sometimes the reason for this drop is a chance event (e.g volcanic eruption or interference by man).
  • The few survivors will posses a much smaller variet of alleles than the original population - there will be much lower genetic diversity.
  • As these individual breed and re-establish, the genetic diversity will remain restricted.
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