Lesson 21: Mechanisms of Evolutionary Change

Genotype

The genetic constitution or makeup of an individual.

Phenotype

The apparent characteristics of an individual resulting from its genotype and environmental factors.

Hardy-Weinberg Principle

explains why populations maintain multiple alleles and why genotype proportions remain constant under certain conditions.

Hardy-Weinberg Equilibrium

A state where genotype proportions remain constant due to no evolutionary forces acting on a population.

Artificial Selection

Deliberate selection for certain characteristics in a population by humans.

Polymorphic Variation

Genetic variation manifesting as different forms, such as a range of flower colors in lupines.

Selection Pressure

Environmental factors that affect survival and reproduction rates, influencing natural selection.

Observable Evolution

Evolutionary changes that can be actively observed in populations with short lifespans.

Evolution

Change in populations of organisms over time, specifically through shifts in allele frequencies within the populations.

Genetic Variation

The presence of different alleles for a trait in a population, which is necessary for any change in allele frequencies to occur.

Mechanisms of Evolutionary Change

Mutation, Gene Flow, Genetic Drift, and Selection.

Mutation

Any change in the base sequence of DNA, ultimate source of genetic variation and giving rise to different alleles.

Gene Flow

The movement of alleles from one population to another, occurring when individuals or gametes move to join a new population.

Genetic Drift

Change in allele frequencies due to sampling error or random chance, which has the largest effect in small populations.

Founder Effect

a few individuals disperse and establish a new population, likely display a different allele frequency or lack certain alleles compared to the original population.

Bottleneck Effect

a population loses genetic variation from a drastic reduction in size (e.g., due to disease, natural disasters), even if the population rebounds, its genetic variability remains lower.

Selection

The process of organisms leaving differential numbers of progeny based on phenotype and behavior.

Natural Selection

A process where environmental conditions affect which individuals produce the most offspring, leading to individuals with favorable variations having higher fitness.

Evolution vs. Natural Selection

Natural selection is the process that leads to evolution, while evolution refers to the historical record of change through time and is the outcome of natural selection or other mechanisms (mutation, gene flow, genetic drift).

Evolutionary Fitness

Reproductive success, with components including survival, mating success, and the number of offspring per mating.

Detecting Evolutionary Processes

Comparing a population's allele and genotype frequencies to those predicted by the Hardy-Weinberg equilibrium; if these frequencies are changing over time, it indicates that evolutionary forces are at work.

Guppy Color Variation Experiment

An experiment demonstrating that in predator-free environments, guppies develop brighter features, while with predators, selection favors duller guppies for camouflage, illustrating observable evolutionary change.

Interaction of Evolutionary Forces

Evolutionary forces can interact, sometimes working together and sometimes in opposition; for example, mutation and genetic drift can counter selection, and gene flow can promote or prevent change in allele frequencies.

Hardy-Weinberg Equilibrium Conditions

No mutations, no gene flow/migration, random mating, very large population size, no selection