Understanding Phenotypes and Genotypes

Phenotype

appearance of a particular characteristic in an organism

Phenotypic ratio

compares the number of each phenotype that is expressed in the offspring

Genotype

genetic makeup of an organism

Homozygous

organism has matching alleles e.g. PP or pp

Homozygous dominant

both alleles give the dominant trait e.g. PP

Homozygous recessive

both alleles give the recessive trait e.g. pp

Heterozygous

organism has non-matching alleles e.g. Pp

Genotypic ratio

compares the number of each genotype that is expressed in the offspring

Complete dominance

all the traits are either dominant or recessive

Incomplete dominance

the hybrid expresses a mixture of the traits displayed by its purebred parents

Codominance

both traits are completely expressed in the hybrid e.g. One parent with Type A blood crosses with one with Type B blood to give offspring of Type AB blood

Sex chromosomes

Female: XX, Male: XY

Sex linkage

sex-linked gene is located on the sex chromosome (X or Y) e.g. X-linked: XR, X', Y-linked: YG, Y⁹