Chapter 14, Problem 38A

Summary Introduction

To infer:

The type of inheritance pattern as represented in the given pedigree.

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. Pedigrees help to determine whether the inheritance patterns are dominant or recessive.

Answer to Problem 38A

The given pedigree illustrates inheritance of a rare genetic disorder calledTay-Sachs disease. It is a recessive genetic disorder.

Explanation of Solution

Tay-Sachs disease- The given pedigree illustrates inheritance of a rare genetic disorder. Tay-Sachs disease is caused by lack of an enzyme involved in lipid metabolism. The missing enzyme causes build- up of lipid in central nervous system which can lead to death.

In this diagram, one child (II3) expresses the disease and others(II1, II2, II4) do not have the disease. The parents (I1 and I2) are carriers of the disease as circles and squares are half filled. Hence we can say that the disorder is a recessive genetic disorder because a recessive genetic disorder will have a carrier. The parents are unaffected but their child is affected indicating that each parent carries a recessive allele; i.e they are heterozygous for the disease causing gene. Recessive disorders are expressed only in homozygous condition. Hence II3 expresses the disease. It must be homozygous for recessive allele.