patterns of inheritance

genetic makeup of an organism

visible characteristic of an organism

a version of a gene

not true-breeding; having different alleles at a particular gene locus on a pair of homologous chromosomes

true-breeding; having identical alleles at a particular gene locus on a pair of homologous chromosomes

determined by a single gene

involving two gene loci

where both alleles present in the genotype of a heterozygous individual contribute to the individual’s phenotype

characteristic for which there are three or more alleles in the population’s gene pool

gene present on (one of) the sex chromosome

gene loci present on the same autosome (non-sex chromosome) that are often inherited together

interaction of non-linked gene loci where one masks the expression of the other; from the greek, ephistanai, meaning ‘stoppage’

statistical test designed to find out if the difference between observed and expected data is significant or due to chance

variation that produces phenotypic variations where the quantitative traits vary by very small amounts between one group and the next

genetic variation producing discrete phenotypes- two or more non-overlapping categories

a type of natural selection that occurs when an environmental change favours a new phenotype and so results in a change in the population mean

when a small sample of an original population establishes in a new area; its gene pool is not as diverse as that of the parent population

a sharp reduction in size of a population due to environmental catastrophes such as earthquakes, floods, disease or human activities such as habitat destruction, overhunting or genocide, which reduces genetic diversity; as the population expands it is less genetically diverse than before

natural selection leading to constancy within a population; intermediate phenotypes are favoured and extreme phenotypes selected against; alleles for extreme phenotypes may be removed from the population; stabilising selection reduces genetic variation within the population

members of a species living in the same place at the same time that can interbreed

formation of two different species from one original species, due to geographical isolation

the splitting of a genetically similar population into two or more populations that undergo genetic differentiation and eventually reproductive isolation, leading to the evolution of two or more new species

formation of two different species from one original species due to reproductive isolation while the populations inhabit the same geographical location

selective breeding of organisms; involves humans choosing the desired phenotypes and interbreeding those phenotypes individually; therefore selecting the phenotypes that contribute to the gene pool of the next generation of these organisms