Variation at the Population Level Flashcards
What is the central issue in population genetics?
Genetic variation
What are the 3 questions about genetic variation in population genetics?
- What is the extent within populations
- Why is it there
- How does it change over many generations
What is the gene pool?
All alleles of every gene in a population
What do population geneticists study?
Genetic variation within the gene pool and how it changes from one generation to the next
What is a phenotype?
Characteristic of an individual organism
What is a genotype?
Genetic constitution of an individual
What is a locus?
Place on a chromosome, gene that occupies a site
What is an allele?
A particular form of a gene, distinguishable by its effects on phenotype
What is a haplotype?
A set of alleles that is a DNA segment that can be distinguished from homologous sequences
What is a gene copy?
Number of representatives of a gene. Ex. 200 gene copies with 100 2N individuals
What is an allele frequency?
Relative proportion of a particular allele at a particular locus in a population, the relative commonness or rarity of an allele
What is a genotype frequency?
Relative proportion of a particular genotype in a population
What is a population?
A group of individuals of the same species living in the same region at the same time
What is a deme?
A smaller local population that is part of a larger population
Why do demes have different gene pools than other demes within a larger population?
They are often isolated by moderate geographic barriers and are more likely to interbreed with each other
How do you calculate the total number of alleles in a diploid population?
Number of individuals x 2
How do you calculate the total number of a certain allele in a population?
Add two copies for each homozygote and one copy for each heterozygote
How do you calculate the allele frequency in a population?
Number of copies of an allele in a population/ total number of gene copies in a population
How do you calculate the genotype frequency in a population?
Number of individuals with a particular genotype in a population/ total number of individuals in a population
What should the total frequency of all alleles add up to?
1
What is a monomorphic gene? What should the allele frequencies be?
A gene with only 1 allele. The frequency will be 1 or close to 1
What is the Hardy-Weinberg equilibrium?
A simple mathematical expression that relates allele frequencies and genotype frequencies in a population
Is the Hardy-Weinberg equilibrium a null or alternative hypothesis?
Null hypothesis. Predicts that allele and genotype frequencies will not change over the course of many generations
What are the 5 assumptions of the Hardy-Weinberg equilibrium?
- No mutations
- No gene flow
- Random mating
- No natural selection
- Extremely large population
What does it mean if the assumptions of the Hardy-Weinberg equilibrium are met?
The population is not evolving
Why does the Hardy-Weinberg equilibrium assume no mutations?
Mutations will modify the gene pool
Why does the Hardy-Weinberg equilibrium assume random mating?
Individuals showing preference in breeding will change genotype frequencies
Why does the Hardy-Weinberg equilibrium assume large populations?
Small populations are very prone to random genetic drift
Why does the Hardy-Weinberg equilibrium assume no gene flow?
Immigration and emigration will change allele frequencies
Why does the Hardy-Weinberg equilibrium assume no natural selection?
Natural selection will lead to certain alleles becoming more common and other alleles becoming less common
What does it mean when any of the Hardy-Weinberg equilibrium assumptions are violated?
The population is evolving
What is the Hardy-Weinberg equilibrium formula for a gene with 2 alleles?
p^2 + 2pq + q^2 = 1
What is p^2 in the Hardy-Weinberg equilibrium formula?
The genotype frequency of homozygous dominant individuals in the population
What is 2pq in the Hardy-Weinberg equilibrium formula?
The genotype frequency of heterozygous individuals in the population
What is q^2 in the Hardy-Weinberg equilibrium formula?
The genotype frequency of homozygous recessive individuals
Does the Hardy-Weinberg equilibrium describe a hypothetical or real population?
Hypothetical. In reality none of the assumptions would likely be met
What is p in the Hardy-Weinberg equilibrium?
Allele frequency of dominant allele
What is q in the Hardy-Weinberg equilibrium?
Allele frequency of the recessive allele
How might a natural population be in Hardy-Weinberg equilibrium?
A population can be evolving at some genes and be in Hardy-Weinberg equilibrium at other genes
How is the phenylketonuria locus in Hardy-Weinberg equilibrium?
It is an autosomal recessive disorder. There is low mutation rate, mate selection is random with respect to that gene, natural selection can only act on homozygous recessive individuals that don’t follow the diet, population is large, and migration has no effect
What does it mean when a population is at Hardy-Weinberg equilibrium?
Allele frequencies are not changing from generation to generation
What are the steps to determine if a population is at Hardy-Weinberg equilibrium?
- Calculate allele frequencies
- Calculate the expected genotype frequencies (using p^2, 2pq, and q^2)
- Multiply genotype frequencies by the population size to get the expected number of individuals
- Compare the genotype frequencies in a population with the expected number of individuals
- If expected number of individuals with that genotype is + or - 5% of the number of individuals with that genotype are the same, the population is at Hardy-Weinberg equilibrium
What is sympatric population variation?
Variation among populations with overlapping geographic distributions
What is parapatric population variation?
Variation among neighbouring populations that are adjacent, but don’t overlap
What is allopatric population variation?
Populations that are separated by geographic barriers
What is a subspecies?
A recognizable distinct population occupying a different geographic area from others of the same species
What is a cline?
Gradual change in a character or allele frequencies over geographic distance
