Chapter 2: Mendelian Genetics Terminology
Allele
An alternative version of a gene that produces variation in a trait (e.g., A or a).
Gamete
A reproductive cell (sperm or egg) that contains one copy of each gene (haploid).
P Generation (Parental Generation)
The original pair of organisms used in a genetic cross.
F1 Generation (First Filial Generation)
The offspring produced from crossing the P generation.
F2 Generation (Second Filial Generation)
The offspring produced by crossing individuals from the F1 generation.
True Breeding
Organisms that consistently produce offspring with the same phenotype when selfcrossed; they are homozygous for a trait.
Reciprocal Cross
Two crosses that swap the sexes of the parents to test whether a trait is sex-linked.
Test Cross
A cross between an individual with an unknown genotype and a homozygous recessive
individual to determine the unknown genotype.
Genotype
The genetic makeup of an organism; the specific alleles it carries.
Phenotype
The observable physical or biochemical traits of an organism.
Dominant
An allele that is expressed in the phenotype when at least one copy is present.
Recessive
An allele that is only expressed in the phenotype when two copies are present.
Heterozygote Genotype
A genotype consisting of two different alleles for a gene (e.g., Aa).
Homozygote Genotype
A genotype consisting of two identical alleles for a gene (e.g., AA or aa).
Law of Segregation
Allele pairs separate during gamete formation so each gamete carries only one allele for
each gene.
Law of Independent Assortment
Alleles of different genes segregate independently during gamete formation (applies to
genes on different chromosomes or far apart on the same chromosome).
Autosomal Inheritance
Inheritance of traits controlled by genes located on autosomes (non-sex chromosomes).
Pedigree
A diagram that tracks the inheritance of a trait through multiple generations of a family.