Polygenic Inheritance and Pleiotropy

Polygenic (multiple-gene) inheritance (fig. 4.17a) is a phenomenon in which genes at two or more loci, or even on different chromosomes, contribute to a single pheno-typic trait. Human eye and skin colors are normal poly-genic traits, for example. They result from the combined expression of all the genes for each trait. Several diseases are also thought to stem from polygenic inheritance, including some forms of alcoholism, mental illness, cancer, and heart disease.

Pleiotropy (ply-OT-roe-pee) (fig. 4.17b) is a phenomenon in which one gene produces multiple pheno-typic effects. Sickle-cell disease, for example, is caused by a recessive allele that changes one amino acid in

Polygenic inheritance

Gene 1

Gene 2

Phenotype

Gene 3

Gene 3

Pleiotropy Examples Humans

Figure 4.17 Polygenic Inheritance and Pleiotropy. (a) In polygenic inheritance, two or more genes combine their effects to produce a single phenotypic trait, such as skin color. (b) In pleiotropy, a single gene causes multiple phenotypic traits, as in sickle-cell disease.

Figure 4.17 Polygenic Inheritance and Pleiotropy. (a) In polygenic inheritance, two or more genes combine their effects to produce a single phenotypic trait, such as skin color. (b) In pleiotropy, a single gene causes multiple phenotypic traits, as in sickle-cell disease.

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Chapter 4 Genetics and Cellular Function 149

hemoglobin. It causes red blood cells (RBCs) to assume an abnormally elongated, pointed shape when oxygen levels are low, and it makes them sticky and fragile. As RBCs rupture, a person becomes anemic and the spleen becomes enlarged. Because of the deficiency of RBCs, the blood carries insufficient oxygen to the tissues, resulting in multiple, far-reaching effects on different parts of the body (see chapter 18).

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  • artemisia
    Is sickle cell anemia polygenic inheritance?
    7 years ago

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