Genetics Terms and Principles: Mendelian Inheritance, Linkage, and Pedigree Analysis

P generation

The parental generation; the first set of individuals crossed.

F1 generation

The first filial generation; offspring of the P cross.

F2 generation

The second filial generation; offspring produced when F1 individuals self-cross or cross with each other.

Dominant

An allele that is expressed when present; masks recessive alleles.

Recessive

An allele expressed only when two copies are present (homozygous recessive).

Homozygous

Having two of the same allele (AA or aa).

Heterozygous

Having two different alleles (Aa).

Phenotype

The observable trait (e.g., purple flowers).

Genotype

The genetic makeup (e.g., PP, Pp, or pp).

Law of Segregation

Each individual has two alleles for every gene, and these alleles separate during meiosis so each gamete receives only one allele.

Law of Independent Assortment

Alleles of different genes separate into gametes independently of one another if the genes are on different chromosomes or far apart on the same chromosome.

Complete Dominance

One allele completely masks another.

Codominance

Both alleles are fully expressed.

Incomplete Dominance

Heterozygote shows a blended phenotype.

Multiple Alleles

More than two possible alleles exist in the population.

Pleiotropy

One gene influences multiple traits.

Epistasis

One gene affects the expression of another gene.

Polygenic Inheritance

Traits controlled by many genes; shows a continuum.

Sex-linked traits

Traits carried on the X chromosome (most common).

Test cross

A test cross determines the genotype of an individual showing a dominant phenotype.

Gene linkage

Linked genes are located close together on the same chromosome.

Pedigree

A pedigree is a chart showing inheritance patterns across generations.