Question

A mutation in the operator locus of lac operon that confers constitutive expression of β-galactosidase is .............

• A. cis dominant
• B. trans dominant
• C. co-dominant
• D. dominant negative

Hint:

In gene regulation, a \textbf{cis dominant} mutation affects the gene's expression on the same DNA strand, while \textbf{trans} mutations act across different molecules.

Answer 1

The Correct Option is A

Step 1: Understanding the lac operon mutation.
The lac operon is a genetic system in bacteria that regulates the breakdown of lactose. Mutations in the operator region can result in constitutive expression, meaning the genes are expressed continuously. A cis dominant mutation means that the mutation affects only the DNA to which it is directly linked, rather than being able to act on other alleles.
Step 2: Analyzing the options.
(A) cis dominant: Correct — This type of mutation affects the operator region on the same DNA strand, causing continuous expression.
(B) trans dominant: Incorrect — Trans mutations affect regions on different DNA molecules.
(C) co-dominant: Incorrect — This term refers to mutations that express both alleles equally, not relevant here.
(D) dominant negative: Incorrect — This refers to mutations that produce a protein that inhibits the activity of the normal protein.
Step 3: Conclusion.
The correct answer is (A) cis dominant because this mutation affects the operator region on the same chromosome, causing constant expression of β-galactosidase.