Vocabulary # 1

Alelle:One of a number of different forms of a gene.

Codominance:Refers to a relationship between two alleles of a gene. 

Dihibrid cross:Is a cross between F₁ offspring (first generation offspring) of two individuals that differ in two traits of particular interest.

Epitasis:Interaction among the products of two or more gene pairs.

F1:The offspring of an initial genetic cross.

F2:The offspring of parents who are the first filial generation from a genetic cross.

Gene:Unit of information for a heritable trait, passed from parents to offspring.

Genotype:Genetic makeup of an organism; a single gene pair or the sum total of an individual's genes.

Heterozygous:Having a pair of nonidentical alleles at a gene locus (that is, on a pair of homologous chromosomes).

Homozygous dominant:Having a pair of dominant alleles at a gene locus (on a pair of homologous chromosomes).

Homozygous recessive:Having a pair of recessive alleles at a gene locus (on a pair of homologous chromosomes).

Hybrid offspring:Of a genetic cross, offspring having a pair of nonidentical alleles for a trait.

Incomplete dominance:Condition in which one allele of a pair is not fully dominant.

Independent assortment :Mendelian theory that by the end of meiosis, each pair of homologous chromosomes (and linked genes on each one) are sorted before shipment to gametes independently of how the other pairs were sorted. Later modified to account for the disruptive effect of crossing over on linkages.

Monohybrid cross:Intercross between two F₁ heterozygotes that are identical for one gene locus.

Multiple allele system:Three or more slightly different molecular forms of a gene that occur among individuals of a population.

Phenotype:Observable trait or traits of an individual that arise from gene interactions and gene-environment interactions.

Pleiotropy:Positive or negative effects on two or more traits owing to expression of alleles at a single gene locus.

Probability:The chance that each outcome of a given event will occur is proportional to the number of ways the outcome can be reached.

Punnett-square method:Construction of a simple diagram as a way to predict probable outcomes of a genetic cross.

Segregation:Mendelian theory. Separation of alleles during gamete formation.

Test cross:Experimental cross to determine whether an individual of unknown genotype that shows dominance for a trait is either homozygous dominant or heterozygous.

True-breeding lineage:Of sexually reproducing species, a lineage in which only one version of a trait appears over the generations in all parents and their offspring.