learning objectives 4 Flashcards
Define evolution in genetic terms.
Evolution is the change in the gene pool over time.
What is a gene?
A gene is a small region of a chromosome that codes for a molecule (usually a protein) which performs a function for a cell.
Define allele frequency.
Allele frequency is the proportion of all the copies of a given gene that are a particular allele.
How is allele frequency calculated?
Allele frequency = Number of a certain allele / Total number of alleles.
What is the convention for allele frequencies?
Frequency of one allele = p; Frequency of the other allele = q; p + q = 1.
Define population in genetic terms.
A population is a group of interbreeding individuals.
What is genotype frequency?
Genotype frequency is the proportion of a specific genotype in a population.
Define genotype count.
Genotype count is the number of individuals with a certain genotype.
What is a gene pool?
A gene pool is the combination of all the genes (including alleles) present in a reproducing population or species.
Why is there a shift in beetle colors through generations?
Due to natural selection, genetic drift, migration from other populations, or mutation.
What is the purpose of testing for Hardy-Weinberg Equilibrium (HWE)?
To measure microevolution by comparing the expected genetic makeup of a population if it were not evolving to the observed population.
What does it mean if observed genotype counts match expected counts under HWE?
The population is not measurably evolving, and mating is random.
What does it mean if observed genotype counts differ from expected counts under HWE?
The population may be evolving, and the differences can provide clues about how.
List the 5 conditions required for a gene in a population to be in HWE.
- No genetic drift (large population)
- No natural selection
- No gene flow/migration
- No new mutation
- Random mating
How do you calculate expected genotype frequencies under HWE?
For alleles p and q:
Frequency of homozygote TT = p²
Frequency of homozygote tt = q²
Frequency of heterozygote Tt = 2pq
What statistical test is used to evaluate whether a population is in HWE?
A chi-squared (χ²) goodness of fit test.
True/False: If p² + 2pq + q² = 1, the population is in HWE.
False, you must compare observed and expected genotype counts with a chi-squared test.
What is genetic drift?
Genetic drift is the change in allele frequencies due to random sampling effects in finite populations.
How does genetic drift affect allele frequencies?
It causes random changes, which are slower in medium/large populations but can reduce genetic variation over time.
Describe the bottleneck effect.
A sudden change drastically and randomly reduces the population size, reducing genetic diversity and changing allele frequencies by chance.
Describe the founder effect.
A small number of individuals start a new population, often with different allele frequencies from the source population due to chance.
Does genetic drift occur in populations that remain the same size?
Yes, genetic drift occurs in every population, in every generation, but is stronger in small populations.
How does natural selection affect allele frequencies?
It can select for some genotypes and against others, changing allele frequencies over time.
What is gene flow, and how does it affect populations?
Gene flow is the transfer of alleles between populations, which can alter allele frequencies, reduce genetic differences among populations, and counteract the effects of natural selection.
What is mutation’s role in evolution?
Mutation introduces new genetic variants and is essential for genetic variation, but its effects on allele frequencies are usually small over short time scales.
Define assortative mating.
Assortative mating is non-random mating where individuals with similar genotypes are more likely to mate, often producing excess homozygotes.
Define disassortative mating.
Disassortative mating is non-random mating where individuals with different genotypes are more likely to mate, often producing excess heterozygotes.
