Question

Read statements a—d.
(a) In transcription, adenine pairs with uracil
(b) Regulation of lac operon by repressor is positive regulation
(c) Human genome has approximately $50,000$ genes
(d) Haemophilia is sex-linked recessive disease
How many of the above statements are correct?

• A. $3$
• B. $2$
• C. $4$
• D. $2$

Answer 1

The correct option is B $2$

Statement a
Transcription is the process of formation of m-RNA from DNA. In DNA, usually adenine pairs with thymine. But in RNA, thymine is replaced with uracil. Thus adenine pairs with uracil in transcription. The given statement a is correct.

Statement b
The repressor protein binds to the operator region, blocking the RNA polymerase and preventing the transcription.
● The regulation of operon by the repressor is called negative regulation.
● The regulation of an operon by the activator protein is called positive regulation.
● Thus, the given statement is incorrect.

Statement c
The total number of genes present in the human genome is estimated to be $30000$.
Thus, the given statement is incorrect.

Statement D
Haemophilia is a X-linked recessive disease in which one of the protein responsible for clotting of blood is affected.
Thus, the given statement is correct.

Final answer
(A) $2$