Genetics Terminology

A collection of key genetics terms and definitions to aid in understanding and studying genetic concepts.

Genotype

An organism’s genetic makeup, or allele combination.

Phenotype

The observable traits of an organism.

Sexual reproduction

Reproduction that combines genetic material from two parents.

Genetic variation

Differences in DNA or traits among individuals.

Diploid

Having two sets of chromosomes.

Haploid

Having one set of chromosomes.

Meiosis

Cell division that produces haploid sex cells.

Sex chromosomes

Chromosomes that determine biological sex.

Autosomes

All chromosomes that are not sex chromosomes.

Homologous chromosomes

A matching pair of chromosomes with the same genes.

Karyotype

An organized picture of a cell’s chromosomes.

Meiosis I

The first meiotic division, where homologous chromosomes separate.

Meiosis II

The second meiotic division, where sister chromatids separate.

Non-sister chromosomes

Chromosomes from different homologous pairs.

Recombination

Exchange of DNA between chromosomes, creating new allele combinations.

Gametes

Haploid sex cells, like sperm and egg.

Zygote

The diploid cell formed when two gametes fuse.

Somatic cells

Body cells that are not sex cells.

Sex cells

Gametes; sperm and egg cells.

Dominant

An allele that shows its effect when present.

Recessive

An allele expressed only when no dominant allele is present.

Allele

A version of a gene.

Monohybrid cross

A cross that tracks one trait.

Law of segregation

Allele pairs separate during gamete formation.

Homozygous

Having two identical alleles for a gene.

Heterozygous

Having two different alleles for a gene.

Probability

The chance that an event will happen.

Addition rule of probability

The chance of either of two mutually exclusive events happening.

Multiplication rule of probability

The chance that two independent events both happen.

Chi-square test

A statistical test that compares observed and expected results.

Law of independent assortment

Alleles of different genes separate independently into gametes.

Dihybrid cross

A cross that tracks two traits.

Pedigree

A family tree that shows how a trait is inherited.