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Mendelian traits behave according to the model of monogenic or simple gene inheritance in which one gene corresponds to one trait. Discrete traits (as opposed to continuously varying traits such as height) with simple Mendelian inheritance patterns are relatively rare in nature, and many of the clearest examples in humans cause disorders.
Complex traits are phenotypes that are controlled by two or more genes and do not follow Mendel's Law of Dominance. They may have a range of expression which is typically continuous. Both environmental and genetic factors often impact the variation in expression. Human height is a continuous trait meaning that there is a wide range of heights ...
Genetic variation can be identified at many levels. Identifying genetic variation is possible from observations of phenotypic variation in either quantitative traits (traits that vary continuously and are coded for by many genes, e.g., leg length in dogs) or discrete traits (traits that fall into discrete categories and are coded for by one or a few genes, e.g., white, pink, or red petal color ...
Typically, QTLs underlie continuous traits (those traits which vary continuously, e.g. height) as opposed to discrete traits (traits that have two or several character values, e.g. red hair in humans, a recessive trait, or smooth vs. wrinkled peas used by Mendel in his experiments).
Many traits are not discrete features (e.g. purple or white flowers) but are instead continuous features (e.g. human height and skin color). These complex traits are products of many genes. [52] The influence of these genes is mediated, to varying degrees, by the environment an organism has experienced.
Characters are unitary, that is, they are discrete e.g.: purple vs. white, tall vs. dwarf. There is no medium-sized plant or light purple flower. Genetic characteristics have alternate forms, each inherited from one of two parents. Today these are called alleles. One allele is dominant over the other. The phenotype reflects the dominant allele.
They can show either smooth, continuous gradation in a character, or more abrupt changes in the trait from one geographic region to the next. [2] A cline is a spatial gradient in a single specific trait, rather than in a collection of traits; [3] a single population can therefore have as many clines as it has traits, at least in principle. [4]
The lack of discontinuities in genetic distances between human populations, absence of discrete branches in the human species, and striking homogeneity of human beings globally, imply that there is no scientific basis for inferring races or subspecies in humans, and for most traits, there is much more variation within populations than between them.