What is a population?
Interbreeding group of individuals that belong to the same species and live within a restricted geographical area.
What are population genetics?
Consequences of Mendelian genetics, a shift from individual to population-level thinking. We do this because the frequency of an allele in a population is often not the same as the ratio from a single Mendelian cross.
Why is population genetics important?
Because changes in allele frequency contribute to evolution.
What are Darwin’s conditions for evolution by natural selection?
- Individuals within a species vary.
- Some variation is passed to offspring (heritability).
- Survival and reproduction is not random, but related to phenotypic variation.
When will evolution by natural selection not occur?
- If there is no variation (might happen if alleles become fixed in a population - only one allele available).
- Variation is not heritable.
- Variation is heritable but has no fitness consequences (reproductive success).
What happens to genetics variation in the absence of evolution?
It will remain unchanged over time (fixed).
How do we test a hypotheses?
- We need to establish that there is something to explain at all (Ex. is evolution happening?).
- A default condition needs to be established, what is being compared against in testing (null hypotheses).
What is our null hypotheses for evolution?
If evolution is change in allele frequencies over time, then null hypothesis should be no change in allele frequencies over time.
What did Hardy and Weinberg use to solve the following question:
What will happen to a single trait, at a single gene, that is encoded by two alleles, in the absence of evolution?
Probability theory was used to solve this problem.
What is the first assumption of the probability model?
A single locus with two alleles does not change state between generations (no mutation). No new alleles arise in the population. Only A and a.
What is the second assumption of the probability model?
Alleles are not added to the population (no gene flow from other populations). No migration will occur between different populations of same species.
What is the third assumption of the probability model?
The population is infinite in theory.
When assuming that a population is infinite, what does this eliminate within evolution?
A large population will lower the chances of changing alleles. Random processes will have a lower effect (no genetic drift). Ex. a wildfire could result in a loss of a large amount of the population, which may shift allele frequency. With a large population, there will be a lesser impact.
What is the fourth assumption of the probability model?
Natural selection does not affect the alleles. All diploid individuals have the same fitness (reproductive success). The probability of surviving to breed is the same, and mating and fertilizing ability is the same.
What is the fifth assumption of the probability model?
There is random mating (reunion of gametes). Ex. throwing a bunch of haploid gametes in a bucket and they come together at random.
What are the conditions of the Hardy-Weinberg equilibrium model? In short?
- No mutation.
- No migration (gene flow).
- Population is infinitely large.
- Genotypes do not differ in fitness (no selection).
- Mating is random.
What is the purpose of the Hardy-Weinberg assumptions? Are they actually possible?
The purpose is that with these conditions, we expect that allele frequency will not change (so they will be in equilibrium). This is not possible in a real life scenario.
Theoretically, if we look at a population with two alleles, how can we represent the frequency of these alleles?
- By using p and q.
- p = freq(A)
- q = freq(a)
- p + q = 1
What is probability theory?
The probability of two independent events occurring together is the product of their individual probabilities. Ex. Probability of A combing with A is gonna be the probability of both gametes multiplied together (P(event 1) x P(event 2)).
What is the expected probability of two dominant gametes mating?
p^2. Or, p x p.
What is the expected probability of two recessive gametes mating?
q^2. Or, q x q.
What is the expected probability of a recessive and a dominant gamete mating?
2pq. Or, 2(p x q).
What do expected genotype frequencies tell us?
That these probabilities will be present under Hardy-Weinberg equilibrium, regardless of the genotypic frequencies of the previous generation.
What can we assume about a population if it is under all Hardy-Weinberg conditions, in relation to genotypic frequencies?
If we allow one round of random mating with all the other conditions met, the population will return to equilibrium.
