BIO A01: Lecture 3 - Hardy-Weinberg and the Agents of Evolution

Vocabulary practice flashcards covering microevolution, allele and genotype frequencies, the Hardy-Weinberg Principle and its equilibrium conditions, and the five evolutionary agents from BIO A01 Lecture 3.

Genotype frequency

The percentage of individuals in a population with a specific genotype, reflecting the distribution of allele combinations such as $AA$, $Aa$, or $aa$.

Allele frequency

The percentage of all copies of a specific gene in a population that carry a particular allele, reflecting the distribution of genetic variants such as $A$ or $a$.

Evolution (genetic definition)

The change in allele frequencies within a population over generations.

Hardy-Weinberg Principle

The principle stating that allele and genotype frequencies in a population remain constant across generations when only Mendelian segregation and recombination are at work, in the absence of evolutionary agents.

Null model

A theoretical baseline representing the genetic makeup of a population if it were not evolving at a specific gene locus, against which real population data can be tested.

Conditions for Hardy-Weinberg Equilibrium

1. No mutations occur; 2. No gene flow (population is closed to migration); 3. Infinite (very large) population size; 4. No natural selection (all genotypes survive and reproduce equally); 5. Random mating with respect to genotypes.

Hardy-Weinberg equation

$p^2 + 2pq + q^2 = 1$, where $p^2$ represents the frequency of the homozygous dominant genotype, $2pq$ represents the heterozygous genotype frequency, and $q^2$ represents the homozygous recessive genotype frequency.

Mutation (evolutionary agent)

A spontaneous, heritable change in DNA that serves as the major primary source introducing novel genetic variation into a population.

Deleterious mutation

A harmful mutation that decreases fitness; lethal mutations result in death, though they may persist in a population when recessive.

Neutral mutation

A mutation that is neither harmful nor helpful, such as a silent mutation that does not alter amino acids or an amino acid substitution that does not affect protein function.

Advantageous mutation

A mutation that benefits an organism and may be favoured by natural selection to increase reproductive success, such as novel host adaptations.

Gene flow

The change in allele frequencies that occurs when individuals or gametes (such as pollen or seeds) move between populations and reproduce.

Genetic drift

Random, chance-driven fluctuations in allele frequencies that have the greatest effect in small populations and tend to reduce genetic variability or eliminate alleles.

Population bottleneck

A drastic, often temporary reduction in population size caused by catastrophic events such as drought, starvation, or disease, which rapidly reduces genetic variation and can lead to allele fixation.

Founder effect

A type of genetic drift that occurs when a small group of individuals colonizes a new location, establishing a new population with allele frequencies that differ by chance from the parent population.

Natural selection

A non-random process where individuals possessing certain heritable traits survive and reproduce at higher rates than others because of those traits.

Relative fitness

The contribution an individual makes to the gene pool of the subsequent generation relative to the contributions made by other individuals in the population.

Directional selection

A form of natural selection that favours phenotypes at one extreme end of the phenotypic spectrum, shifting the mean phenotype.

Stabilizing selection

A form of natural selection that favours individuals with intermediate phenotypes over individuals with extreme phenotypes, narrowing variation.

Disruptive selection

A form of natural selection that favours individuals at both phenotypic extremes over individuals with intermediate traits.

Nonrandom mating

The selection of mates based on specific phenotypes and genotypes, which alters genotype frequencies and prevents genetic equilibrium without directly changing allele frequencies.