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AS/A-level Biology - Genetic Diversity and Adaptation

Genetic Diversity and Adaptation

· Mutation,natural selection,gene flow,adaption,A-level Biology
  • As the number of alleles increases so does genetic diversity in a population.
  • Genetic diversity allows natural selection to occur.
  • Evolution is a change in a populations' alleles and genotypes from generations to generations. Therefore it should be considered at a population level.

When it comes to AS/A-level Biology, do you know what are the factors that affect the proportion of both homozygote and heterozygote?

Five factors affect the proportion of homozygote and heterozygote:
 

(1) Genetic drift

  • This is a change in the gene pool that occurs in a small population due to chance.
  • Two situations can lead to genetic drift:

(i) Population Bottlenecks - This is when a large number of a population is wiped out due to disease, natural disasters or overhunting.
(ii) Founder Effect - This is when a new colony is found by a small number of individuals.

(2) Gene flow

  • This is the movement of alleles from one population to another when a member moves into another population.
  • The variety of alleles that this member has can significantly affect the gene pool of a population especially if it has good survival and mating skills.

(3) Mutations

  • These are changes to an organism's DNA.
  • The change is transferred to gametes which immediately changes the gene pool.
  • This is a rare event but the cumulative effect is massive.
  • Mutations themselves play an insignificant role in changing the frequency of alleles in a population.
(4) Non-random mating
  • Homozygous individuals increase when preferred organisms mate with each other, causing frequency of genotypes to differ significantly from equilibrium values.
  • Populations consist of individuals with different genetic make-ups.
  • This means that Hardy-Weinberg equilibrium is not maintained.
(5) Natural selection
  • Populations consist of individuals with different genetic make-ups.
  • Colourful and vibrant organisms are more susceptible to predation.
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Directional Selection

  • It happens in bacteria.
  • E.g. Bacteria are resistant to antibiotics leading to an increase in the frequency of the allele that is resistant to antibiotics.

Stabilising Selection

  • It happens in a changing environment and occurs in the natural selection of birth mass in humans.
  • Extremes of the phenotype range are selected leading to a reduction in variation.

References:

1. https://www.storyboardthat.com/storyboards/4f2c9e8a/rabbit-natural-selection-

That’s the end of the topic!

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Drafted by Bonnie (Biology)

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