Mendelian traits are defined by their discrete or discontinuous nature, meaning their phenotypic expressions are distinctly categorized without any overlapping forms. A prime example of this is the ABO blood group system, which includes four phenotypes that are entirely separate, with no intermediate types between A and B. In essence, Mendelian traits display clear-cut variations rather than a continuous spectrum.
On the other hand, polygenic traits exhibit a wide range of phenotypic expressions, forming a graded series or continuum. Unlike Mendelian traits, which are influenced by a single genetic locus, polygenic traits arise from the combined effects of alleles at two or more loci. Each of these loci contributes to the overall phenotype.
Most observable phenotypic variation in humans can be attributed to polygenic traits, which have historically been used in racial classification. skin, hair, and eye color, numerous other characteristics such as stature, facial shape, and fingerprint patterns are polygenic. Due to their continuous nature, these traits can be quantified along a scale with equal increments.
For instance, height is typically measured in feet and inches or meters and centimeters. When measuring the height of a large population, the resulting data would show a continuous distribution from the shortest to the tallest individuals. This continuous variation is characteristic of polygenic traits. The ability to measure these traits enables physical anthropologists to employ various statistical analyses for a deeper understanding of human diversity.
For Mendelian traits, the approximate or precise locations of genetic loci are well documented, allowing for the examination of inheritance mechanisms and patterns at these specific sites. In contrast, such detailed studies are not yet feasible for polygenic traits, these traits are influenced by a multitude of genes, each of which may contribute only a small effect to the overall phenotype. As a result, the specific genetic loci associated with polygenic traits are still being identified and traced
