Genetics Flashcards
A woman (but not her husband) suffers from Von Willebrand disease, an autosomal dominant condition that shows 50% penetrance. This condition is expected to be phenotypically expressed in what percent of her offspring?
25% Individuals with autosomal dominant diseases are almost always heterozygotes, as the possession of two mutated alleles is nearly always lethal. Therefore, this woman has a 50% chance of passing the Von Willebrand allele to each of her children. Due to the mentioned penetrance value, such a child then has a 50% chance of expressing the trait. (0.5)(0.5) = 0.25, or 25%.
A student performs a research study on a type of plant that expresses either waxy or smooth leaves, depending on the dryness of the season. The student obtains the following data on preferential expression and genetic analysis. What can be concluded from this data?
The trait for waxy leaves displays incomplete penetrance. We can see that the expression of this gene varies based on the season, but the percentage of members with the trait in the population remains constant over time. This means that, at times, at least some plants who have the gene are not expressing its associated trait. This indicates that there is penetrance of less than 100%. We can make no conclusions about expressivity because we do not know how waxy the leaves are.
The ability of a cell to express multiple self-surface protein markers, each coded for by an allele variant from the same gene and carrying out its own independent function, is an example of:
Codominance. Codominance is the idea that two dominant phenotypes can be expressed simultaneously without a blend. For example, two dominant colored parents may produce a striped child. The ability to produce multiple proteins from the same gene is an example of codominance, because multiple phenotypes are co-existing simultaneously.
Describe the difference between expressivity and penetrance.
Penetrance is the idea in genetics that - for an individual with a certain genotype - there is a certain likelihood that the corresponding phenotype will or will not be expressed. Will or will not have the trait?
Expressivity is the idea that genes can be expressed to different extents, leading to a variable resultant phenotype. How much of the trait?
