Question

The phenomenon of expression of only one allele of an immunoglobulin gene in lymphocytes is known as

• A. Allelic exclusion
• B. Allelic inclusion
• C. Allelic variation
• D. Allelic heterogeneity

Answer 1

The Correct Option is A

Allelic exclusion is a biological mechanism that ensures only one allele of an immunoglobulin (Ig) gene is actively transcribed and translated in a single B-cell. This prevents the expression of multiple Ig specificities, allowing a B-cell to produce a single type of antibody. 

Step 1: Understanding Allelic Exclusion - Every B-cell has two alleles for immunoglobulin genes, one from each parent. - However, to maintain antigen specificity, only one allele is expressed, while the other remains inactive. - This process ensures that each B-cell produces only one type of antibody, preventing the creation of mixed or non-functional antibodies. 

Step 2: Evaluating the Options - Option (A) - Correct: Allelic exclusion ensures that a single allele is expressed in a given B-cell to maintain antigen specificity. - Option (B) - Incorrect: Allelic inclusion would imply both alleles are expressed, which does not happen in functional B-cells. - Option (C) - Incorrect: Allelic variation refers to different genetic variations in a population, not the selective expression in a cell. - Option (D) - Incorrect: Allelic heterogeneity means different mutations in the same gene cause similar diseases, unrelated to immunoglobulin gene expression. 

Step 3: Conclusion Since allelic exclusion ensures that a B-cell expresses only one allele for immunoglobulin genes, the correct answer is option (A).