How are "gene penetrance" and "gene expressivity" different?
A. With penetrance, the gene is either expressed completely or is not expressed at all. With expressivity, the gene is always expressed but the degree of expression can range from minor to extreme.
B. Penetrance and expressivity are both related to "gene dosage." With penetrance, only one copy of the gene is expressed and, with expressivity, more than one copy of the gene can be expressed.
C. Gene penetrance and gene expressivity are merely different terms for the same concept, overexpression of recessive alleles.
D. Penetrance refers to the actual gene structure in the DNA and expressivity refers to the chromosome locus of the gene.
A
A dominant gene may be present and normal (or abnormal) and not expressed consistently in all people who have that gene or allele. This situation is referred to as reduced penetrance. The gene is present but either is or is not expressed. Expressivity refers to variation in degree of expression. The gene (and its alleles) is present and expressed, but in some people the phenotype may be so slight that the trait is barely seen, and in other people the phenotype may be so strong it cannot be missed.
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