CHT HLA Genetics & Molecular Biology 3

Question 1

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

Accepted Answer

Trans (in-trans) DQ pairing

Answer

Allelic exclusion

Answer

Haplotype imbalance

Answer

MHC restriction

Question 2

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

Accepted Answer

HLA-B

Answer

HLA-A

Answer

HLA-DRB1

Answer

HLA-C

Question 3

What is a 'null' allele in HLA nomenclature?

Accepted Answer

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

Answer

An allele with no sequence polymorphism vs. reference

Answer

An allele shared by all human populations

Answer

An allele encoding only intracellular protein

Question 4

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

Accepted Answer

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

Answer

Class II presents endogenous peptides; class I presents exogenous peptides

Answer

Both present endogenous peptides but to different lymphocyte subsets

Answer

Class II requires β2-microglobulin; class I does not

Question 5

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

Accepted Answer

Resolves phase ambiguities and provides allele-level phased genotypes

Answer

Requires less DNA template

Answer

Faster turnaround for all clinical cases

Answer

Does not require PCR amplification

Question 6

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

Accepted Answer

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

Answer

HLA-C is not polymorphic and therefore not typed

Answer

HLA-C is only relevant for bone marrow transplantation

Answer

HLA-C mismatches have no immunological significance