A phenotypic trait, or simply a trait, is defined as a distinct variant of a phenotypic characteristic of an organism, meaning that it is a measurable and observable expression of one or more genes. Some common human traits include the degree to which the earlobe merges with the head, the extent to which the terminal phalanx of the thumb can be bent backwards (where thumbs that can be bent relatively far are known as of "hitchhiker's thumbs"), and the ability to roll the lateral edges of the tongue into a tube. A common misconception about these three traits is that they are controlled by a single locus in an inheritance model, or what are called simple Mendelian traits. Say no to plagiarism. Get a tailor-made essay on “Why violent video games should not be banned”?Get an original essayIn the case of distal hyperextensibility of the thumb attachment and earlobe, a continuous distribution may be observed , most individuals having thumbs or ears with values, not one of two distinct values ​​in each case. Glass and Kistler (1953) arbitrarily classified thumbs capable of bending at an angle equal to or greater than 50 degrees as "hitchhiker's thumbs." They found that many individuals possessed one thumb that qualified as a hitchhiker's thumb and one that did not, but classified the individuals as having the hitchhiker's thumb trait. They described that distal thumb hyperextensibility did not appear to be affected by age or gender, and that in general people with hitchhiker's thumb did not exhibit any other type of double joint. They also observed that this trait might have a skeletal basis and not simply be due to longer ligaments after studying x-rays of the thumbs of a man who had only one thumb classified as hyperextensible. A study of the lead author's family pedigree over 3 generations revealed no evidence that the trait was not a simple autosomal recessive. In a family study by Glass and Kistler (1953) of 192 families, they concluded (using formulas derived from Snyder's (1934) Hardy-Weinberg principle) that thumb type was a simple Mendelian trait, with l allele of a right thumb. being dominant, despite the fact that a mating of two people with straight thumbs produced a child with a hitchhiker's thumb. They explained that this was due to a case of incomplete penetrance, or in other words, that other genes or non-genetic factors also influence the trait. Earlobes can be broadly classified into two types, free and attached, although they display a continuous distribution, similarly. to distal hyperextensibility of the thumb. Lai and Walsh (1966) classified “attached” earlobes as those in which the lowest point of the earlobe was the point of attachment to the head and all others as “free.” They studied two groups of subjects; a series of 160 families with 347 children from the western highlands of New Guinea, and a second group composed of 6 populations around the world. They found no differences in the distribution of earlobe types between men and women or between different age groups. In a family study of 160 families, they tested the possibility that the earlobe phenotype could be due to a single genetic effect using the Hardy-Weinberg principle, assuming that the responsible gene is autosomal dominant or autosomal recessive. They also tested the possibility that the phenotype could be due to.