lecture 21 - population genetics & natural selection Flashcards
What is the principle of the Hardy-Weinberg equation?
The genetic variation in a population will remain constant from one generation to the next, in the absence of disturbing factors
What is the formula for the Hardy-Weinberg equation?
p^2 + 2pq + q^2 = 1
In the Hardy-Weinberg equation, what do the symbols p and q represent?
p = frequency of dominant allele, q = frequency of recessive allele
What is the sum of p and q in the Hardy-Weinberg equation?
1
How is frequency of alleles expressed?
As a proportion/decimal
What are the drivers of change in allele frequency (7)?
non-random mating, random genetic drift, mutation, bottleneck effect, founder effect, natural selection, gene flow/migration
What is random genetic drift?
A random change in allele frequencies due to random sampling error over generations. Often leads to a reduction in genetic variation as certain alleles can be lost over time.
What is the bottleneck effect?
Genetic drift that occurs when a population is severely reduced, removing alleles from the population and reducing genetic variation.
What is the founder effect?
An extreme example of genetic drift that occurs when a small population (containing few alleles) breaks away from the large population and forms another seperate colony, which has limited genetic variation.
What phenomenon causes the founder effect?
Migration
What is stabilising selection?
Natural selection that favours the ‘average’ phenotype, so the distribution curve of the phenotypes gets narrower and higher over time.
What is directional selection?
Natural selection that favours an extreme phenotype, meaning the distribution curve of phenotype becomes skewed to the left or right over time. The symmetrical normal distribution then reestablishes with a new mean closer to the extreme.
What is disruptive selection?
Natural selection that favours traits at 2 opposite extremes, because two niches can be occupied, creating a distribution with two peaks, with few individuals with the mean phenotype.
How does sexual selection affect genetic variation?
Sexual selection allows certain phenotypes to be more successful in reproducing, meaning their genes will be passed on, increasing their frequency in the population.
What is frequency-dependent selection?
The fitness of a certain group is dependent on the phenotype of another population. As the favoured phenotype increase in prevelance, so too will the fitness of the species, leading to an increase in the frequency of the alleles of the group.
