Population Genetics – Key Vocabulary

A set of vocabulary flashcards summarizing essential terms, formulas, and applications introduced in the lecture on population genetics.

Population Genetics

The biological field that studies the genetic composition of populations and how it changes over time under forces such as mutation, migration, selection, and genetic drift.

Evolution (Modern Definition)

Genetic changes within a population occurring over successive generations.

Mendelian Population

A group of interbreeding, sexually-reproducing individuals that share a common gene pool; the basic unit of study in population genetics.

Gene Pool

The complete set of all alleles present at every locus in all individuals of a population.

Genotypic Frequency

The proportion of individuals in a population that carry a particular genotype; calculated as number with the genotype divided by total individuals (∑ frequencies = 1).

Allelic Frequency

The proportion of all copies of a gene that is made up by a particular allele; reflects the true gene pool and also sums to 1 for a locus.

Hardy-Weinberg Law

A principle stating that genotype and allele frequencies in a large, randomly-mating population remain constant from generation to generation in the absence of evolutionary forces.

Hardy-Weinberg Equation

For a bi-allelic locus: p² + 2pq + q² = 1, where p and q are allele frequencies of A and a, respectively.

p (Allele Frequency)

Symbol commonly used for the frequency of the first (often dominant) allele at a locus.

q (Allele Frequency)

Symbol commonly used for the frequency of the second (often recessive) allele at a locus; p + q = 1.

Formula: p From Genotypes

p = f(AA) + ½ f(Aa); derives allele A frequency from genotype frequencies.

Formula: q From Genotypes

q = f(aa) + ½ f(Aa); derives allele a frequency from genotype frequencies.

Allele Counting Method

Calculating allele frequency by directly tallying all copies of each allele and dividing by total alleles (2N in diploids).

Genotype Inference Method

Calculating allele frequency by converting known genotype frequencies into allele frequencies using p = f(AA)+½f(Aa) etc.

Natural Selection

Differential survival or reproduction of genotypes leading to changes in allele frequencies; driven by heritable variation in fitness.

Mutation (Recurrent)

A continual source of new alleles that can alter allele frequencies over time.

Migration (Gene Flow)

Movement and interbreeding of individuals between populations, introducing new alleles and changing frequencies.

Genetic Drift

Random fluctuations in allele frequencies due to sampling error, especially in small populations.

Codominance

Inheritance pattern in which both alleles in a heterozygote are fully expressed, e.g., MN blood group (LM, LN).

Multiple Alleles

Presence of more than two alternative forms of a gene in a population, e.g., ABO blood group (IA, IB, i).

X-Linked Gene Frequency

Because males have one X chromosome, their genotypic frequency for an X-linked locus equals allele frequency, simplifying calculations.

Fitness

Relative reproductive success of a genotype, influencing its contribution to future generations.

Phenotypic Variation

Observable differences among individuals, much of which is heritable and forms the basis for natural selection.

Application: Disease-Risk Alleles

Population genetics helps identify and interpret allele variants associated with health and disease across regions.

Application: Adaptive Traits in Pathogens

Determining genes that confer virulence or drug resistance, guiding public-health interventions.

Antibiotic/Drug Resistance

Evolutionary increase in frequency of alleles that enable pathogens to survive treatments; monitored through population genetics.

Temporary Assemblage

Concept that diploid genotypes are dismantled each generation during gametogenesis, whereas allele frequencies persist.