Population Genetics

Concept 10: Genetic Diversity & Allele Frequency

Success Criteria

  • I can define the terms gene pool, genetic diversity, and allele frequency.

Vocabulary

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Gene pool & genetic diversity

Gene pool is all the alleles held by the individuals in a population.

Genetic diversity is the variation of genotypes in a gene pool. Having many different combinations of alleles may offer a survival advantage to a species if environmental conditions change.

In small island populations, there is possibility of interbreeding and this can lead to low genetic diversity. In large populations, there are more individuals, therefore a greater chance of random mating which will result in greater genetic diversity.

Allele frequency & allele fixation

Allele frequency is the percentage of each allele in a gene pool.

Allele fixation is the change in a gene pool from a situation where there is at least two alleles in a population to a situation where only one of the alleles remains for a particular gene.

When the allele frequency is 100%, the allele is said to be ‘fixed’.

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There are four factors that cause changes to the allele frequency within a gene pool:

  1. Natural selection

  2. Mutation

  3. Migration

  4. Genetic drift

SciPAD

Page 157 - Genetic Biodiversity and Allele Frequency

Education Perfect

Task called 'Concept 10: Allele Frequency'

Concept 11: Natural Selection & Mutant Alleles

Success Criteria

  • I can discuss how natural selection acts on gene pools.

  • I can explain how mutant alleles contribute to evolution and genetic change.

Vocabulary

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Transformation

Do Now

Calculate the allele frequencies of the population of beads shown.

Natural Selection

Success Criteria:
I can discuss how natural selection acts on gene pools.

Individuals with alleles best adapted to the environment will survive and reproduce, and pass these favourable alleles onto their offspring and therefore the gene pool.

Better suited alleles increase in frequency, and less suited alleles decrease in frequency in the gene pool. Non-favourable alleles will be lost from the population as it is selected against due to its lower chance of survival and reproduction.

Selection pressures may reduce the frequencies of certain alleles.

For example. the phenotype produced by the allele combination aa is more vulnerable to frost.

Mutations

Success Criteria:
I can explain how mutant alleles contribute to evolution and genetic change.

Mutation is the permanent change in the gene sequence, giving a new allele to a population.

Mutant alleles can enter the gene pool if they occur in gametes. They can also become established in the gene pool if the allele is beneficial, and gives the individual a higher chance of survival and reproduction.

Peppered moths are a classic example of a beneficial mutation selected for by natural selection.

Task 1: Watch this video.

Task 2: SciPAD

Page 158-159 - Evolution and Darwin

Page 160 - Mechanisms for Evolution - Natural Selection

Page 161 - Natural Selection and the Importance of Genetic Variation

Page 165 - Mechanisms for Evolution - Mutation

Task 3: Education Perfect

Task called 'Concept 11: Natural Selection and Mutations'

Concept 12: Gene Flow & Genetic Drift

Success Criteria

  • I can explain how gene flow affects the genetic biodiversity of both small and large populations.

  • I can discuss the impact of genetic drift on the allele frequency both within and between populations.

  • I can compare and contrast the founder effect and the bottleneck effect.

Vocabulary

Energy

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Transformation



Gene Flow

Success Criteria:
I can explain how gene flow affects the genetic biodiversity of both small and large populations.

Migration is when individuals moving into or out of a population.

These individuals can only contribute their alleles to the gene pool if they interbreed with individuals in the new population (i.e. after successful reproduction). This is called gene flow.

Migration may increase the frequency of alleles in a gene pool by adding alleles (immigration of individuals), or decrease the frequency of alleles by removing alleles (emigration of individuals).

Stop watching at 6:10

Genetic Drift

Success Criteria:
I can discuss the impact of genetic drift on the allele frequency both within and between populations.
I can compare and contrast the founder effect and the bottleneck effect.

Genetic drift is the random change in allele frequency of a population, due to chance.

The frequency of the alleles can change through chance, especially if the population is or becomes small. In small populations, relatively small changes in allele numbers can have a big impact on the allele frequency in the total population.

Founder Effect

The founder effect describes the gene pool of a small population that was established from a subset of a larger population. As the founder population is small, it is likely subject to genetic drift.

The allele frequency of the founder population may not be representative of the allele frequency of the original population. Therefore, there could be less genetic diversity in founder effect populations.

Bottleneck Effect

It is possible for populations to suddenly be reduced to very small numbers due to catastrophic events (e.g. floods, volcanic eruptions, landslide) and heavy predation or disease.

The bottleneck effect is where a species is reduced to a few individuals and then recovers with low genetic diversity. The small population will be subject to genetic drift.

SciPAD

  • Page 167 - Migration (Gene Flow)

  • Page 168 - Genetic Drift and The Founder Effect

  • Page 169 - The Bottleneck Effect

  • Page 170 - Modelling the Founder Effect and Bottlenecks

  • Page 172 - Writing Extended Answers - Genetic Change

  • Page 173 - Genetic Change - The Tuatara

  • Page 174 - Genetic Change - The Possum

Education Perfect

Task called 'Concept 12: Gene Flow and Genetic Drift'