Science 1.9 Key Words

Words you must learn

Allele

Different forms of the same gene. They can be dominant or recessive.

Trait

A genetically determined characteristic.

Genotype

The particular alleles of an organism.

Phenotype

The observable characteristics of an individual resulting from its genotype.

Purebred

An organism that is homozygous for a particular trait.

Homozygous

An individual with two alleles that are the same for a particular trait.

Heterozygous

An individual with two alleles that are different for a particular trait.

Pedigree Chart

A diagram that shows the phenotypes of related individuals.

Test cross

A cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait so the unknown genotype can be determined from the offspring.

Dominant

An allele which is always expressed, even if only one is present. Expressed with an upper-case letter (i.e. ‘A’).

Recessive

An allele which is only expressed when two of them are present. Expressed with a lower-case letter. (i.e. ‘b’).