Name: __________________
Genetics Terminology
Use the space to write definitions that will help you understand. There is no point having
complicated definitions that make no sense to you! Use examples if it helps!
Gene Allele –
Dominant Trait Recessive Trait –
P Generation -
F1 Generation F2 Generation –
Purebred -
Hybrid -
Genotype Phenotype –
Monohybrid Cross -
Homozygous -
Heterozygous -
Probability Punnett Squares –
Mendelian Ratio –
Principle of Dominance –
Law of Segregation –
Law of Independent Assortment –
Test Cross -
Name: __________________
Genetics Terminology
Gene - region of the chromosome that governs the expression of a
particular trait, ex. height
Alleles - alternate forms of a gene, ex. types of height: tall or short
Genotype - the genetic make-up of an organism (written in the form of
alleles)
Phenotype - the physical appearance of the trait in an organism (what it
looks like)
Homozygous - having two of the same alleles for a trait
Heterozygous - having two different alleles for a trait
Dominant Trait - a characteristic that is always expressed in an individual
if at least one dominant allele is present
Recessive Trait - a characteristic that is expressed when it is the only
allele present
Purebred - organisms that share similar traits inherited from ancestors, ex.
flower colour (all homozygous)
Hybrid - when a cross between two different purebred organisms results in
an organism that is heterozygous
Monohybrid Cross - a cross where only one trait is being observed/tested,
ex. height
P Generation - parent generation
F1 Generation - first filial generation (first set of offspring)
F2 Generation - second filial generation (second set of offspring)
Probability - the chance of a particular outcome, usually expressed as a
ratio
Punnett Squares - simple chart used to calculate the probability of
inheriting a particular trait
Mendelian Ratio - ratio of dominant phenotype (homozygous dominant
genotype and heterozygous genotypes) to recessive phenotype
(homozygous recessive genotype)
 special ratio of 3:1 when heterozygotes are crossed for one trait
 special ratio of 9:3:3:1 when heterozygotes are crossed for two
traits
Principle of Dominance - when individuals of contrasting traits are
crossed, the offspring will express only the dominant trait
Law of Segregation - states that inherited traits are determined by genes
which segregate (separate) in the gametes, with one in each gamete.
Test Cross - cross of an individual of unknown genotype with a
homozygous recessive individual, used as a method to determine the
unknown genotype