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HLA Genetics & Molecular Biology Flashcards

6 cards from real CHT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What phenomenon occurs when a heterozygous individual at HLA-DQA1 and HLA-DQB1 can form up to four different DQ heterodimers?

    Answer: Trans (in-trans) DQ pairing

    In heterozygous individuals, DQA1 and DQB1 chains from opposite chromosomes can pair in trans, generating up to four different DQ heterodimers.

  2. The HLA system is the most polymorphic genetic system in the human genome. Which locus currently has the greatest number of recognized alleles?

    Answer: HLA-B

    HLA-B has the greatest number of recognized alleles of any HLA locus, with thousands catalogued in the IMGT/HLA database.

  3. What is a 'null' allele in HLA nomenclature?

    Answer: An allele with a stop codon or splice mutation resulting in no cell-surface expression

    Null alleles (designated 'N' in the allele name) harbor mutations such as premature stop codons that prevent surface expression of the HLA protein.

  4. Which feature distinguishes HLA class II molecules from class I in terms of their antigen presentation?

    Answer: Class II presents exogenous peptides to CD4+ T cells; class I presents endogenous peptides to CD8+ T cells

    HLA class II molecules present peptides derived from extracellular (exogenous) antigens via the endosomal pathway to CD4+ helper T cells.

  5. In NGS-based HLA typing, what is a key advantage over Sanger sequencing?

    Answer: Resolves phase ambiguities and provides allele-level phased genotypes

    NGS typing can resolve cis/trans (phase) ambiguities that Sanger sequencing cannot, producing fully phased allele-level results.

  6. What is the clinical significance of HLA-C typing in solid organ transplantation?

    Answer: HLA-C mismatches contribute to rejection and are included in some matching algorithms

    HLA-C is polymorphic and mismatches at this locus have been associated with rejection outcomes, so many programs include it in compatibility assessments.