Certified Histocompatibility Specialist 2025 – 400 Free Practice Questions to Pass the Exam

In the context of heterozygous Sequence-Based Typing (SBT) for HLA-Cw alleles, the presence of a deletion within exon 3 will have specific effects on the resulting sequence data. The correct choice indicates a situation where there is a normal sequence followed by consecutive positions that show mostly heterozygosity.

This scenario suggests that after the normal sequence, the deletion causes disruption, leading to discrepancies in the expected nucleotide sequences at those positions. Due to the nature of a deletion, one allele is missing a nucleotide compared to the other allele, which would result in varying patterns during sequencing. In heterozygous individuals, the presence of a deletion on one allele implies that sequencing may reveal differences where one allele presents a normal sequence while the other has the deleted nucleotide, thus typically appearing as consecutive variants or heterozygosity in subsequent bases.

This situation will stand out on the electropherogram as it contrasts with other scenarios where one might only see an absence of nucleotides uniformly (indicating the potential absence of one allele) or slight abundances and variability in nucleotides that lack the definitive pattern that indicates a deletion specifically. Thus, understanding this concept is critical in confirming the diagnosis of the deletion through careful interpretation of