Discontinuous and continuous variation

Discontinuous variation Describes the qualitative differences between phenotypes. There are no intermediate categories eg blood group, male or female. Different alleles at a single gene locus have large effects on the phenotype Different gene loci have quite different effects on the phenotype Eg= codominance, dominance and recessive patterns of inheritance. Continuous variationThis describes quantitative differences between phenotypes. These are phenotypic differences where there is a wide range of variation within the population, with no distinct categories. Eg- height, mass, length, yield and size. Traits exhibiting continuous variation are controlled by two or more genes Each gene provides an additive component to the phenotype Different alleles at each gene locus have a small effect on the phenotype A large number of different genes may have a combined effect on the phenotype. These are known as polygenes and the characteristics they control is described as polygenic. These genes are unlinked they are on separate chromosomes.