July 22, 2021
- 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.
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!
Drafted by Bonnie (Biology)