Figure Polygenic inheritance in grain colour of wheat. Examples of such quantitative traits or characteristics in humans or animals of high order are height, weight, intelligence and that of plants include size, shape, and color of plants. In polygenic inheritance patterns, the characters do not show clear cut differences unlike in monogenic inheritance patterns. They portray a combination of the character inherited from both parents. In summary, it is of great importance to understand these inheritance patterns in order to understand the manner in which different traits are expressed in organisms.
The two main forms monogenic inheritance and polygenic inheritance represents the traditional Mendelian inheritance pattern and the later discovered Non — Mendelian inheritance patterns, respectively. In these two patterns, the inheritance is governed by the number of genes involved in determining the particular trait or phenotype or character of an organism.
Thus, monogenic, as the name suggests, uses one gene to determine a character; in contrast, polygenic patterns involve more than one gene to give rise to a single character.
This is the difference between monogenic and polygenic inheritance. The study of the genes involved in these inheritance patterns is important as it helps to study mutations of genes which give rise to genetic disorders and to build up genetic relationships among organisms for a common character and thereby evaluate evolutionary traits.
You can download PDF version of this article and use it for offline purposes as per citation notes. Available here. Samanthi Udayangani holds a B. Degree in Plant Science, M. Your email address will not be published. Leave a Reply Cancel reply Your email address will not be published. Monogenic vs Polygenic Inheritance. Monogenic inheritance is an inheritance pattern which determines a particular trait by one set of alleles or a specific gene.
In simple words, polygenic inheritance occurs the single phenotypic trait is controlled by two or more genes. Therefore, multiple genes interact with each other additively to influence a phenotypic trait. The inheritance of a phenotypic trait can be measured quantitatively. Polygenic inheritance can be observed in many different organisms, including humans and drosophila.
Height, skin colour, eye colour and weight are several examples of polygenic inheritance in humans. In polygenic inheritance, traits often show a phenotypic spectrum rather than showing clear-cut categories. For example, skin pigmentation in humans shows a phenotypic spectrum since it is controlled by several different genes.
Similar to pleiotropy, polygenic inheritance does not follow patterns of Mendelian inheritance. Pleiotropy is the phenomenon in which a single gene affects multiple phenotypic traits or phenotypes. Therefore, this particular gene does not code for a single characteristic. It contributes to multiple unrelated characteristics. For example, the gene coding for seed coat colour is not only responsible for seed coat colour; it contributes to flower and axil pigmentation as well.
In humans, there are many examples of pleiotropic genes. Marfan syndrome is a disorder which shows pleiotropy. One gene is responsible for a constellation of symptoms, including thinness, joint hypermobility, limb elongation, lens dislocation, and increased susceptibility to heart disease. Moreover, phenylketonuria PKU is one of the most widely cited examples of pleiotropy in humans. A defect in the gene coding for the enzyme phenylalanine hydroxylase results in the multiple phenotypes associated with PKU, including mental retardation, eczema, and pigment defects.
Many important genetic disorders are associated with a single gene and thus exhibit Mendelian patterns of inheritance. Cystic fibrosis is a well-known example. The gene involved with this disorder has a "normal" variant and another variant that causes cystic fibrosis.
Cystic fibrosis, however, is a recessive trait, so you have to inherit two copies of the disease-causing variant to have the disorder -- one copy from mom and one from dad. The ratio of children who have the disorder to children who do not can be predicted based on the variants that the parents have and the simple ratios that Mendel used to predict inheritance in his pea plants. Polygenic traits are much more complex than Mendelian traits.
Rather than being shaped by a single gene alone, a polygenic trait is influenced by multiple genes. In humans, eye color and skin color are two of the most well-known examples. There isn't a single gene for darker brown or lighter white skin; rather, there are multiple genes, and the combination you inherit determines your skin color. Many different combinations are possible, so humans exhibit many different shades of skin color.
Predicting how a Mendelian trait will be inherited is fairly straightforward.
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