Classical Genetics!

Genotype

Genetic makeup (genes); ex. TT or Tt or tt.

Phenotype

Observable trait (gene product); ex. Brown or white fur color.

Allele

Different versions of a gene; ex. yellow and green pea seeds or T or t.

Homozygous

Both alleles for a trait are the same; ex. TT or tt.

Heterozygous

Both alleles are different; ex. Tt.

True-Breeding

If allowed to self-pollinate, they would produce offspring identical to themselves; ex. homozygous dominant or recessive (TT or tt).

Hybrid

The offspring of two different true-breeding varieties; ex. heterozygous (Tt).

Dominant

When only one of the two different alleles in a heterozygous individual appears to affect the trait; represented by an upper-case letter.

Recessive

The allele that seems to be suppressed by the dominant allele in the heterozygous state; represented by a lower-case letter.

Mendel’s Law of Dominance

In the heterozygous state, the dominant trait will be expressed in the phenotype.

Mendel’s Law of Segregation

The two alleles for a character separate during the formation of gametes.

Monohybrid Cross

A mating event between two individuals involving one gene.

Test Cross

Breeds an individual of unknown genotype but dominant phenotype, with a homozygous recessive individual in order to figure out whether the parent is homozygous dominant or heterozygous for a given trait.

Mendel’s Law of Independent Assortment

Genes located on different chromosomes will be inherited independently of each other.

Linked Genes

Genes located on the same chromosome that tend to be inherited together in genetic crosses.

Dihybrid Cross

Cross between two individuals that includes two completely different traits; ex. Eye color & hair color.

Incomplete Dominance

Both alleles are dominant and the heterozygote shows an intermediate phenotype.

Co-dominance

When heterozygous for two dominant traits, the individual expresses both traits separately.

Multiple Alleles

There are more than two alleles available for a gene; ex. blood types.

Antigen

A substance that can trigger an immune response causing the production of antibodies as part of the body's defense against infection and disease.

Rh-factor

An antigen that is found on red blood cells.

Polygenic inheritance

Traits controlled by multiple genes.

Carrier

Carries the recessive allele, but does not show the recessive phenotype.

Pedigree

A diagram that shows the pattern of inheritance of a gene in a family.