Selective Breeding

Process of choosing and breeding speicific organisms for particular physical features or behaviours.

Example: Appaloosa Horse of the Rocky Mountains.

True Breeding

Organisms that are homozygous for a particular trait or set of traits and produce offspring that exhibit the same characteristics generation after generation.

Example: Mendel's Pea plants that cross pollinated and produced offsprings with the same traits.

Dominant

Describes a trait which always appears in an individual that is either heterozygous (Aa) or Homozygous (AA) for that trait.

Example: The allele for purple coloured flower is dominant over the allele for a white coloured flower.

Complete Dominance

A condition in which the dominant allele of a gene completely conceals the presence of the recessive allele of a gene; an individual with one recessive and one dominant allele has the same observable physical characteristic as an individual with two dominant alleles.

Example: When a pink and white flower are crossed, and the offspring produced are all pink, it shows that pink flowers completely dominate white flowers.

Genotype

The combination of alleles for any given trait.

Example: Blood type.

Phenotype

The visible physical and physilogical traits of an organism

Example: Hair colour.

Test Cross

Cross of n individual of an unknown genotype with a homozygous recessive individual: used as a method to determine the unknown genotype.

Example: Crossing YY x yy.

Dihybrid Cross

Cross of two individuals that differ in two traits.

Example: Crossing a pea plant for shape and colour.

Co-dominance

Describes a situation in which two alleles may be expressed equally; occurs when two different alleles for a trait are both dominant.

Example: A roan horse has both black and white hair mixed throughout his body.

Incomplete Dominance

A condition in which neither o two alleles for the same gene can completely conceal the presence of the other.

Example: Cross between a red and white flower that produces a pink flower.