Genetics and Evolution (14 & 22)

Law of Segregation

Alleles separate during gamete formation; each gamete receives one allele.

Law of Independent Assortment

Alleles of different genes separate independently during meiosis.

Gene

A segment of DNA that codes for a trait.

Allele

A version or form of a gene.

Genotype

The genetic makeup of an organism (AA, Aa, aa).

Phenotype

The physical expression of a trait.

Homozygous

Two identical alleles for a gene.

Heterozygous

Two different alleles for a gene.

Complete Dominance

Dominant allele fully masks recessive allele.

Incomplete Dominance

Heterozygote shows an intermediate/blended phenotype.

Codominance

Both alleles are fully expressed.

Sex Linked Trait

A trait associated with a gene located on a sex chromosome, often affecting one sex more than the other.

Evolution

Change in allele frequencies in a population over time.

Hardy Weinberg Equilibrium

No evolution if no mutation, migration, drift, selection, or nonrandom mating occurs.

Genetic Drift

Random change in allele frequencies, strongest in small populations.

Bottleneck Effect

Sudden population reduction causing loss of genetic diversity.

Founder Effect

Small group colonizes a new area, shifting allele frequencies.

Directional Selection

Favors one extreme phenotype.

Disruptive Selection

Favors both extremes

selects against intermediates.

Stabilizing Selection

Favors intermediate phenotypes.

Balanced Polymorphism

Maintains multiple alleles in a population.

Prezygotic Isolation

Prevents mating or fertilization.

Postzygotic Isolation

Hybrids fail to develop or are sterile.