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Chapter 10. Multifactorial Inheritance and Gene × Environment Interactions

Suppose that a condition, blueism, occurs commonly in a population of individuals. After careful genetic analysis of hundreds of people in the population, you discover three different genes that are located on three different chromosomes (blueism 1, blueism 2, and blueism 3). A mutation in any one of these genes can cause this condition. From this information you can conclude that:

A. blueism exhibits multifactorial inheritance.

B. blueism exhibits polygenic inheritance.

C. there are marked environmental influences on blueism.

D. there is no environmental influence on blueism.

E. blueism exhibits genetic heterogeneity.

E is the correct answer.

Different genes at different loci producing the same phenotype is genetic heterogeneity (more exactly locus heterogeneity). This is not consistent with the definitions of polygenic or multifactorial inheritance. Although the environment could obviously modify the phenotype, that is not the explanation for the three different loci.

Which of the following is true about conditions that show a multifactorial inheritance pattern?

A. The recurrence risk is lower if more than one family member is affected.

B. If the expression of the disease in the proband is more severe, the recurrence risk is lower.

C. The recurrence risk is higher if the proband is of the less commonly affected sex.

D. The recurrence risk for the disease is quite high even in remotely related relatives.

E. Environmental influences are not important.

C is the correct answer.

Refer to the list of characteristics of multifactorial inheritance in this chapter. For choices A, B, and D the information is the opposite of what is true. Of course E is wrong, because environmental influences are central in multifactorial inheritance.

Assume that nose size is inherited in a polygenic manner. Based on this you would predict that:

A. at least 50 different genes contribute to the size of the nose.

B. a person with a big nose who mates with a person with a small nose would most likely have children with normal sized noses.

C. there would be a high threshold effect for persons with few liabilities for a large nose.

D. a survey of the population ...

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