Adaptations, Constraints, and Genetic Drift

Vocabulary terms and definitions covering fitness landscapes, evolutionary constraints, trade-offs, genetic drift, probability errors, and heterozygosity calculations.

Fitness Landscape

A theoretical, three-dimensional model used to visualize adaptations and solutions to biological problems, where vertical peaks represent higher fitness and valleys represent lower fitness.

Phylogenetic Constraint

The evolutionary limitation where an organism is stuck with ancestral traits and cannot de-evolve down into a valley of lower fitness to reach an alternative or superior adaptation.

Fitness

The overrepresentation or underrepresentation of a particular genotype or phenotype in the next generation.

Heterozygote Advantage

A genetic condition in which heterozygous individuals have higher fitness than homozygous individuals.

Balanced Lethal System

A genetic system in Crested Newts where homozygous individuals ($AA$ or $BB$) die, leaving only heterozygotes to survive and causing $50\%$ of the population to die every generation.

Developmental Constraint

A biological limitation during organismal development that restricts adaptive paths, such as upright walking restricting the human birth canal while brain size increased, requiring humans to be born exceptionally early.

Allometric Scaling

A pattern where a specific trait (such as antler size in elk) increases relative to body size at a faster rate than body size itself increases.

Life History Traits

A bundle of organismal characteristics and reproductive strategies, including lifespan, age at sexual maturity, reproductive frequency, and the number of eggs or offspring produced.

Genetic Drift

A strictly random evolutionary mechanism rooted in probability that alters allele frequencies across every population in every generation.

Type I Error

A statistical error that occurs when a test yields a false positive result.

Type II Error

A statistical error that occurs when a test yields a false negative result.

March to Homozygosity

The evolutionary process driven by genetic drift where, given sufficient time without other forces acting, all alleles except one are randomly lost from a population.

Fixation

The point at which an allele reaches a frequency of $100\%$ in a population, resulting in zero remaining genetic variation for that gene.

Heterozygosity

A mathematical measurement of standing genetic variation and gene diversity, calculated as $1 - (p^2 + q^2)$, which reflects the probability of producing heterozygous individuals in the next generation rather than the direct proportion of existing heterozygotes.

Homozygosity

A mathematical measurement representing the total proportion of homozygous genotypes within a population, calculated as $p^2 + q^2$.