Chapter 11, Problem 6A

Summary Introduction

Introduction:

A pedigree uses symbols to illustrate the inheritance of trait. By analyzing the pedigree we can infer the genotypes by observing the phenotypes. Phenotypes of entire family are analyzed to determine the family genotypes. Pedigrees help to determine whether the inheritance patterns are dominant or recessive. The given pedigree illustrates inheritance of a rare genetic disorder called Huntington’s disease.

Answer to Problem 6A

Correct answer :

The correct answer is option B. 2males, 1 female

Explanation of Solution

Explanation/justification for the correct answer:

Option B. 2males, 1 female - Huntington’s disease is a dominant genetic disease. In a pedigree diagram, symbols are used to illustrate the inheritance of a trait. Males are represented by squares and females are represented by circles. One who is affected by the trait is represented by dark, or filled square or circle and one who is unaffected is represented by unfilled square or circle. In the given pedigree, there are 2 affected squares and 1 affected circle. Therefore there are 2 affected males and 1 affected female.

Hence this is the correct option.

Explanation for incorrect answer:

Option A. 1 male, 2 females- In the given pedigree, there are 2 affected squares and 1 affected circle. Therefore there are 2 affected males and 1 affected female. Hence this is not the correct option.

Option C. 1 male, 1 female- In the given pedigree, there are 2 affected squares and 1 affected circle. Therefore there are 2 affected males and 1 affected female. Hence this is not the correct option.

Option D. 2 males, 2 females- In the given pedigree, there are 2 affected squares and 1 affected circle. Therefore there are 2 affected males and 1 affected female. Hence this is not the correct option.