Question

Read the following four statements (A-D).
(A) In transcription, adenosine pairs with uracil.
(B) Regulation of lac operon by repressor is referred to as positive regulation.
(C) The human genome has approximately 50,000 genes.
(D) Haemophilia is a sex linked recessive disease.

Which of the above statements are correct?

• A. B and C
• B. A, C and D
• C. A, B, C and D
• D. A only
• E. D only

Answer 1

The correct option is E D only

Adenosine is a nucleoside composed of adenine molecule attached to a ribose sugar molecule via a glycosidic bond. In transcription, adenine pairs with uracil, not adenosine. Regulation of lac operon by inducer-repressor is referred to as negative regulation and its regulation by CAP-cAMP is referred to as positive regulation. According to human genome project, the human genome has approximately 20,500 genes instead of earlier estimation of 50,000 genes. Hemophilia is an X-linked recessive disorder. The associated genes are located on the X chromosome. Since, males are hemizygous for X-chromosome (have only one X chromosome), one copy of the affected gene in each cell is sufficient to cause the disorder (X${}^h$Y). Females have two X chromosomes and hence, need two copies of the affected gene to cause the disorder (X${}^h$X${}^h$).

Thus, the correct answer is option E.