An Introduction to Genetic Analysis.

Molecular bases of penetrance and expressivity

Mendel was performing his classical experiments with pea planta that have very clear-cut phenotypes. The plant was either with purple or white flowers, with yellow or green seeds, etc. However, when working with human disorders time to time we would observe certain traits that should be expressed but they are not, or they will be expressed but with varying degrees among the offspring [1, 2]. The advancement of the Molecular Genetics allowed for better understanding of the mechanisms underlying these phenomena [3].

Can you find examples of traits that show penetrance or varying expressivity not only in humans but in other organisms as well? Can you find explanation from a molecular point of view what the underlying mechanism is?

1. Griffiths AJF, Miller JH, Suzuki DT, et al. An Introduction to Genetic Analysis. 7th edition, New York: W. H. Freeman; 2000.

2. Miko, I. (2008) Phenotype variability: penetrance and expressivity. Nature Education 1(1):137

3. Zlotogora, J. Penetrance and expressivity in the molecular age. Genet Med 5, 347–352 (2003)

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