Chapter 11, Problem 5A

Summary Introduction

Introduction:

Scientists study family history using a diagram that traces inheritance of a particular trait through several generations. Such diagrams are called pedigree. 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.

Answer to Problem 5A

Correct answer :

The correct answer is option D. Huntington’s disease

Explanation of Solution

Explanation/justification for the correct answer:

Option D. Huntington’s disease - The given pedigree illustrates inheritance of a rare genetic disorder. In this diagram, some express the disease and some do not have the disease. There are no circles or squares which are half filled; so there are no carriers of the disease. Hence we can say that the disorder is a dominant genetic disorder because a recessive genetic disorder will have a carrier. Amongst the diseases given only Huntington’s disease is a dominant genetic disease. The other three are recessive genetic disorders.

Hence this is the correct option.

Explanation for incorrect answer:

Option A. cystic fibrosis- It is a recessive genetic disorder. Since the given pedigree does not show any carrier of the disease, it may be concluded that the pedigree shows a dominant genetic disorder. Hence this is not the correct option.

Option B. albinism- It is a recessive genetic disorder. Since the given pedigree does not show any carrier of the disease, it may be concluded that the pedigree shows a dominant genetic disorder. Hence this is not the correct option.

Option C. Tay-Sachs disease- It is a recessive genetic disorder. Since the given pedigree does not show any carrier of the disease, it may be concluded that the pedigree shows a dominant genetic disorder. Hence this is not the correct option.