7.1-7.4

Evolution

A change in the genetic makeup of a population over generations.

Natural Selection

The process where heritable traits that improve survival or reproduction become more common in a population.

Population

A group of the same species living in the same area that can interbreed.

Adaptation

A heritable trait that increases fitness in a specific environment, or the process of becoming better suited.

Variation

Differences in traits among individuals within a population.

Heritability

The extent to which a trait is genetically passed from parents to offspring.

Differential Survival

When individuals with certain traits are more likely to survive under specific conditions.

Differential Reproduction

When individuals with certain traits leave more offspring than others.

Fitness

Reproductive success measured by the number of surviving offspring produced.

Selective Pressures

Environmental factors that favor some traits over others, shaping which individuals survive and reproduce.

Biotic

Living components of the environment that can act as selective pressures.

Abiotic

Nonliving environmental factors that influence survival and reproduction.

Environmental Stability

How constant or variable environmental conditions are over time.

Genetic Diversity

The variety of alleles and genotypes present in a population.

Genetic Variation

Differences in DNA and traits among individuals within a population.

Mutations

Random changes in DNA that can create new alleles and new traits.

Phenotype

An organism’s observable traits, influenced by genes and the environment.

Directional Selection

Selection that favors one extreme form of a trait.

Stabilizing Selection

Selection that favors the average trait and acts against extremes.

Disruptive Selection

Selection that favors both extremes of a trait over the intermediate form.

Phenotypic Variation

Differences in observable traits (like color, size, or behavior) among individuals in a population.

Heritable Traits

Traits that are encoded by genes and can be passed from parents to offspring.

Genetic Recombination

The reshuffling of alleles during meiosis that creates new combinations in gametes.

Independent Assortment

The random distribution of different chromosome pairs into gametes during meiosis.

Random Fertilization

The chance pairing of one unique sperm with one unique egg to form a zygote.

Peppered Moths

A classic example where moth color frequencies shifted with pollution levels on tree bark.

Sickle Cell Trait

The heterozygous condition for the sickle-cell allele that provides resistance to malaria with few or no symptoms.

Heterozygote Advantage

When individuals with two different alleles (heterozygous) have higher fitness than either homozygote.

Balanced Polymorphism

The stable maintenance of two or more alleles in a population due to selective forces.

DDT Resistance in Insects

An example where pesticide use selected for insects with resistance alleles, increasing their frequency rapidly.

Artificial Selection

Human-directed breeding where people choose which organisms reproduce to increase desired traits.

Genetic Diversity

The variety of alleles and genes present within a population.

Gene Pool

All the alleles for all genes in a population at a given time.

Genetic Bottlenecks

Sharp reductions in genetic diversity when only a few individuals contribute genes to future generations.

Convergent Evolution

Different lineages independently evolve similar traits because they face similar selective pressures.

Allele Frequencies

The proportions of different alleles in the gene pool.

Point Mutations

Changes to a single base in DNA (such as silent, missense, or nonsense).

Chromosomal Mutations

Large-scale changes in chromosome structure, like deletions, duplications, inversions, or translocations.

Genetic Drift

Random changes in allele frequencies, strongest in small populations.

Bottleneck Effect

A sharp reduction in population size that reduces genetic diversity by chance.

Founder Effect

When a small group starts a new population with an allele mix that differs from the original population.

Gene Flow

Movement of alleles between populations through the migration of organisms or gametes.

Population Size

The number of individuals in a population, which affects how strongly chance processes act.

Speciation

The formation of new species when populations diverge enough to stop interbreeding.