Chapter 11, Problem 1A

Summary Introduction

To determine:

Term for the person who is heterozygous for a recessive disorder.

Introduction:

Genes are made up of DNA. DNA provides instruction which determines various traits or characteristics. Different variety or version of gene are called alleles. For every gene a child inherits two alleles − one from the paternal side and other from the maternal side. These alleles together are referred to as genotypes.

When two alleles are same, it is known as homozygous genotypes while when two different types of alleles are present, it is called as heterozygous genotypes.

The relation between the between the two alleles affects the traits that is expressed and also determines the characteristics the person carries.

Explanation of Solution

When two alleles for a trait is inherited by a person from both the parents, one of the alleles expresses itself more strongly and is called dominant alleles. While the other allele, which is masked by dominant allele is called as recessive alleles.

Often a mutated gene can cause genetic conditions resulting in disorder or disease. The expression of DNA is altered by mutation leading to these genetic or sex-linked disorders.

Dependent on the condition, the mutated gene might be dominant or recessive in nature. If the mutated gene is recessive in nature, and is present in a heterozygous individual, it fails to express it. The dominant non-mutated or normal gene covers the effect of mutated recessive gene. However, the person is said to be ‘carrier’ because he himself might not show any symptoms of the disorder due to the heterozygous alleles but may pass this recessive mutated gene to his offspring.

Conclusion

Thus, the person who is heterozygous for a recessive disorder is called as a carrier as he might transfer the recessive disorder gene to next generations.