Which of the following represents invalid molecular nomenclature?

The molecular nomenclature for HLA (Human Leukocyte Antigen) genes is governed by specific guidelines that allow for a standardized way of naming alleles based on their genetic sequences. The correct representation of HLA alleles typically includes a gene name, followed by an asterisk, and then a series of numbers that specify the allele's unique characteristics.

In the case of molecular nomenclature standards, "A20101" does not conform to the expected format for identifying HLA allele equivalents. In particular, the gene designation "A2" is not valid since it improperly combines the gene and its designation; proper nomenclature would simply reference the gene as "A" followed by its allele number with an asterisk, such as "A0101" instead.

This distinction is essential for clarity and to ensure uniformity across the scientific community. Violation of these nomenclature standards can lead to confusion regarding the identification and sharing of genetic data, particularly in translational medicine and compatibility testing for organ transplantation.