Lecture 17. The Principles of Population Genetics Flashcards
What does genetic variation diploid populations arise from ?
Mutation and sexual reproduction
What does mutation allow ?
New variants
What does sexual reproduction allow ?
Variations to be continuously recombined in unique formations
What are a pair of homologous chromosomes defined by ?
Their ability to pair up during meiosis
What is a locus ?
A fixed position on a chromosome
What are alleles ?
Alternate versions of the DNA sequences that occur at the same locus on homologous chromosomes
What are the most commonly observed types of mutation ?
Single nucleotide variant
What is the genotype ?
The genetic material possessed by an individual at a given locus
What is the gene pool ?
The sum of all alleles in the breeding members of a population at any given time
In a diploid population of N individuals how many N alleles is there at an autosomal locus ?
2N alleles
What do we describe the gene pool in terms of ?
Allele and genotype frequencies
What is the formula for allele frequency F(A) ?
Allele count/Total number of alleles
What is the formula for a biallelic variant ?
F(A) + F(a) = p + q = 1
What is a single nucleotide polymorphism ?
A relatively common single nucleotide variant
What is a minor allele ?
Low frequency in the population
What is the major allele ?
Higher frequency in population
What is the genotypic frequency formula F(AA) ?
Genotype count/Total number of individuals
What is the genotypic frequency for a biallelic variant ?
F(AA) + F(Aa) + F(aa) = 1
What is a core concept if we have observed the genotype frequencies of a population ?
We can calculate the allele frequencies
What is a core concept about knowing the allele frequencies of a population ?
We can predict the expected genotype frequencies
When is a population in hardy weinberg equilibrium ?
If its observed genotype and allele frequencies do not change through the generations. They remain constant
What does it take to bring genotypes to equilibrium proportions ?
One generation if random mating
What does hardy weinberg equilibrium require ?
- Random combination of alleles at each generation - random mating
- No change in allele frequencies between generations - no evolution
What are some violations to random mating ?
- Geography ie setting a limit
- Phenotype
- Interbreeding
What is the principle of random mating ?
All other individuals in the population must be equally likely to be chosen as a mate
What is a characteristic of the Wahlund effect ?
Lack of heterozygotes
What is the wahlund effect
Non random mating
What does non-random mating not change ?
Allele frequencies
Is a population in hardy weinberg equilibrium evolving ?
No
If there is still random mating in the observed genotype what will their frequencies do ?
They will match those expected within any single generation
What are the violations in the hardy weinberg equilibrium that lead to evolution ?
- Mutation
- Genetic drift
- Gene flow/migration
- Selection
What does mutation do ?
Changes the allele frequency by creating a new variant
How will a mutation change the minor allele frequency at an invariant locus ?
Change it from 0 to 1/2N
What is genetic drift also known as ?
Sampling error
What is genetic drift ?
Alleles are sampled at random from the gene pool to contribute to the next generation
In genetic drift, when is error smaller ?
The larger the sample size
Where is random drift stronger ?
In smaller populations
Where is random drift weaker ?
In larger populations
What are some extreme examples of genetic drift ?
- Population bottleneck
2. Founder effect
What is population bottleneck ?
Reduction in overall population size due (chance)
What is the founder effect ?
Isolation of a small fraction of the population from the larger group
What is gene flow ?
The movement of genetic material from one population to another
What does isolation lead to ?
Divergence in allele frequencies
What is genetic differentiation ?
Accumulation of allele frequency differences due to restricted gene flow
What allows for gene flow ?
A reduction in the barriers to mating
What is admixture ?
Gene flow between two or more genetically distinguishable populations
What can be considered if gene flow is high enough ?
The two populations can be considered a single random mating population
What happens if gene flow is low enough ?
Subpopulations can be detected through allele frequencies differences called population structure
Where are clines observed ?
When gene flow occurs more frequently between neighboring groups
Why are populations always evolving ?
- Mutation is inevitable
- Population sizes are finite
- The earth is dynamic - continuous isolation and flow
What is selection ?
A non-random change in allele frequencies due to interactions between phenotype and environment
