Target Exam

CUET

Subject

Biology

Chapter

Principles of Inheritance and Variation

Question:

Identify the autosome-linked recessive disorder.

Options:

Myotonic dystrophy

Color blindness

Thalassemia

Haemophilia

Correct Answer:

Thalassemia

Explanation:

The correct answer is Option (3) → Thalassemia

Thalassemia : This is also an autosome-linked recessive blood disease transmitted from parents to the offspring when both the partners are unaffected carrier for the gene (or heterozygous). The defect could be due to either mutation or deletion which ultimately results in reduced rate of synthesis of one of the globin chains (α and β chains) that make up haemoglobin.

Color Blindness: It is a sex-linked recessive disorder due to defect in either red or green cone of eye resulting in failure to discriminate between red and green colour. This defect is due to mutation in certain genes present in the X chromosome. It occurs in about 8 per cent of males and only about 0.4 per cent of females. This is because the genes that lead to red-green colour blindness are on the X chromosome. Males have only one X chromosome and females have two. The son of a woman who carries the gene has a 50 per cent chance of being colour blind. The mother is not herself colour blind because the gene is recessive. That means that its effect is suppressed by her matching dominant normal gene. A daughter will not normally be colour blind, unless her mother is a carrier and her father is colour blind.

Myotonic dystrophy : An example of an autosomal dominant condition is myotonic dystrophy. Myotonic dystrophy is an inherited disorder that causes muscle weakness and myotonia (inability of muscles to relax after use), which becomes more severe over time. Specific problems in other systems of the body can also occur.

Haemophilia is a sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding.