What is the definition of haploinsufficiency?

• A. Presence of extra genetic material
• B. One functional copy that does not produce a normal phenotype
• C. Two functional copies working together
• D. Loss of genetic information

Answer: (B)

Haploinsufficiency refers to a situation in which one functional copy of a gene is not sufficient to bring about a normal phenotype. This typically occurs when one allele of a gene is mutated or deleted, leaving only one remaining functional allele. If that single functional allele does not produce enough gene product (such as protein) to meet the biological requirements of the organism, the result is a phenotype that deviates from normality.

In essence, haploinsufficiency illustrates the concept that some genes require both copies to be functional to ensure normal development or function. This understanding is important in genetics as it can explain certain disease mechanisms where a single mutated allele contributes to a disorder due to the insufficiency of the remaining functional gene copy.

This concept is distinct from the presence of extra genetic material or the complete loss of genetic information. It focuses specifically on the inadequate functionality of one gene copy, which is critical for understanding certain genetic conditions, particularly those involving dominant mutations.