Question

A modifier gene a. must cause disease. b. alters the expression of a disease. c. must be in linkage disequilibrium with the disease allele. d. all of the above. e. none of the above.

Short answer

Answer: A modifier gene alters the expression of a disease.

Step-by-step solution

Understand Modifier Genes

A modifier gene is a gene that has an indirect effect on the expression of another gene. It does not directly cause a disease but can affect the severity, onset, or presentation of a disease caused by another gene.

Evaluate Each Option

Now let's evaluate each option based on the definition and characteristics of a modifier gene: a. must cause disease: Incorrect, as a modifier gene does not directly cause the disease but rather affects the expression of another gene causing the disease. b. alters the expression of a disease: Correct, as a modifier gene can affect the severity, onset, or presentation of a disease caused by another gene. c. must be in linkage disequilibrium with the disease allele: Incorrect, as a modifier gene does not necessarily have to be in linkage disequilibrium with the disease allele. d. all of the above: Incorrect, as not all the statements are correct. e. none of the above: Incorrect, as option b is true.

Choose the Correct Option

Based on the evaluation of options, the correct answer is: b. alters the expression of a disease