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Genetic Drift & HWE
Intro to Evolution
| Question | Answer |
|---|---|
| What is evolution? | A change in allele and genotype frequencies in a population over generations |
| What are the four mechanisms that cause evolution? | Natural selection, genetic drift, gene flow, and mutation |
| What is genetic drift? | A change in allele frequency due to random chance or sampling error, completely independent of an organism's fitness |
| What are the core features of genetic drift? | It is unbiased, causes genetic variation to be lost, makes initially identical populations different, and leads to allele fixation or loss without selection |
| How does population size affect genetic drift? | Genetic drift has a much stronger and more noticeable impact in smaller populations, where alleles can be fixed or lost quickly |
| What is effective population size (N_e)? | The number of individuals in an ideal population that would show the exact same rate of genetic drift as the real population |
| How does effective population size (N_e) affect adaptation in flies vs. humans? | Adaptation is more precise in species with large N_e. Flies (large N_e) have ~50% codon differences from adaptation and 50% from drift; humans (small N_e) have ~15% from adaptation and 85% from drift. |
| What is purifying selection vs. neutral mutation? | Purifying selection removes harmful non-synonymous mutations in coding regions under selective constraint. Neutral mutations occur at sites free of selection and are driven by drift |
| What is the Founder Effect? | The loss of genetic variation when a small group immigrates to establish a new population, carrying a non-random subset of genes from the source population (e.g., red imported fire ants) |
| What is the Bottleneck Effect? | A sudden, drastic reduction in overall population size that leads to a severe loss of genetic diversity (e.g., Northern elephant seals) |
| What is the purpose of Hardy-Weinberg Equilibrium (HWE)? | It acts as a null hypothesis describing a non-evolving population where allele frequencies remain constant across generations |
| What are the 6 assumptions required for a population to be in HWE? | Random mating No natural selection No genetic drift No gene flow No mutations Infinitely large population size |
| What are the HWE allele frequency formulas and symbols? | p + q = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele |
| What are the HWE genotype frequency formulas and symbols? | p^2 + 2pq + q^2 = 1, where p^2 = homozygous dominant, 2pq = heterozygous, and q^2 = homozygous recessive |
| How do you calculate the expected number of individuals for a genotype in HWE? | Expected Count = Genotype Frequency x Total Population Size |
| What is the formula for the Chi-Square (X^2) test in HWE? | X^2 = ∑ (Observed - Expected)^2/Expected |
| How many degrees of freedom (df) are used for a standard 3-genotype HWE Chi-Square test? | df = Number of categories - 1 = 3 - 1 = 2 |
| What does a Chi-Square test p-value ≤ 0.05 indicate? | Reject the null hypothesis; the population deviates significantly from HWE and evolution is occurring |
Created by:
bbrdd