Question

recharge
skin color
multiple choice question
the diagram shows a model of the relationship between the genotypes and phenotypes of the polygenetic trait of skin tone. the model shows possible shades of skin tone from three sets of alleles. in reality, the trait is thought to involve more than three genes.
which statement best describes the changes in the graph if the model included 10 sets of alleles?

• the graph would change so that it was bell shaped but the frequency increases for every set of alleles after 6.
• the graph would change so that it was bell shaped but that the bell was more narrow.
• the graph would change so that is was no longer a bell curve, but a straight line with increasing frequency for every set of alleles.
• the graph would change so that it was bell shaped but that the bell was wider.

Explanation:

This question is about polygenic inheritance (skin color as a polygenic trait). When more gene sets (alleles) are added to a polygenic trait model, the distribution of phenotypes (skin tone here, related to number of dominant alleles) follows a bell - shaped curve (normal distribution). With 3 gene sets, we have a certain bell - curve width. When we increase the number of gene sets to 10, the range of possible dominant alleles (and thus phenotypes) increases, leading to a wider bell - shaped curve. The first option is incorrect as frequency doesn't just increase after 6. The second option is wrong because more genes lead to a wider, not narrower, curve. The third option is incorrect as polygenic traits still follow a bell - curve, not a straight line.

Answer:

The graph would change so that it was bell shaped but that the bell was wider.