A Hypothetical Condition in Some Domesticated Fowl Is Identified Phenotypically

Multiple Choice

A hypothetical condition in some domesticated fowl is identified phenotypically by patchy loss of feathers on the animals' backs. Although several factors, genetic and environmental, are found to be involved, only about 3% of any population with any of these factors are found with feather loss. Which of the following is a likely cause?

A) continuous variation
B) high number of alleles in one of the genes
C) low mutation frequency
D) threshold of liability
E) high number of environmental effects