Key terms
Locus: The location of a gene on a chromosome.
Homologous chromosomes: Chromosome pairs, one from each parent, that are similar in length, gene position and centromere location. Diploid cells (2n) contain these.
Allele: A version of a same gene. They specify different versions of the same trait. These are found in the same position or locus.
Phenotype: Observable characteristics of an organism.
Genotype: Alleles present within cells of an individual, for a particular trait or characteristic.
Dominant: Characteristic in which the allele responsible is expressed in the phenotype, even in those with heterozygous genotypes.
Recessive: Characteristic in which the allele responsible is only expressed in the phenotype if there is no dominant allele present.
Homozygous: Where both alleles in a pair are identical, AA, aa, RR, rr.
Heterozygous: Where the alleles in a pair are different, Aa, Rr
Autosome: Any chromosome that is not a sex chromosome (these are allosomes).
P, F1 and F2:
P – parental generation
F1 – First (filial) generation offspring
F2 – Second (filial) generation offspring
Filial means ‘denoting the offspring of a cross’.