Chapter 13, Problem 13STP

Summary Introduction

To list and classify:

Three genetic disorders and name of the affected organ.

Introduction:

Genetic disorders result from inheritance of traits which are either dominant or recessive. Most disorders are due to recessive alleles but some disorders like Huntington’s disease is due to dominant allele. Pedigrees help to determine whether the inheritance patterns are dominant or recessive.

Answer to Problem 13STP

S.no	Name of genetic disorder	Classification	Organs affected
1	Huntington’s disease	Dominant genetic disorder	Nervous system, muscular system
2	Cystic fibrosis	Recessive genetic disorder	Mucus producing glands, sweat glands, lungs, pancreas and digestive system
3	Tay-Sachs disease	Recessive genetic disorder	Brain

Explanation of Solution

Huntington’s disease: It is a rare genetic disorder in whichsome express the disease and somedo not have the disease. Thedisorder is a dominant genetic disorderso it will be expressed in both homozygous (for dominant gene) and heterozygous condition. An unaffected person will be homozygous recessive for the gene. The disease affects the nervous system. Symptoms of the disease include gradual loss of brain function, uncontrolled movements and emotional disturbances.

Cysticfibrosis: It is a recessive genetic disorder in which the patient secretes thick mucus from glands. The disease affects the mucus producing glands, sweat glands and digestive enzymes. This mucus clogs the respiratory pathways and ducts in pancreas which interrupts digestion. Thick mucus is produced because the cells are unable to absorb chloride ions due to some faulty gene.

Tay-Sachs disease: It is a recessive genetic disorder. It is identified by a cherry red spot on the back of the eye. TSD is caused by the absence of enzymes responsible for breaking down fatty acids called gangliosides. The gangliosides accumulate in the brain causing mental retardation.