CHT HLA Genetics & Molecular Biology 1 — Questions and Answers
Question 1: Which chromosome carries the HLA gene complex in humans?
- Chromosome 6 (Correct answer)
- Chromosome 7
- Chromosome 9
- Chromosome 12
Correct answer: Chromosome 6
The HLA gene complex (MHC) is located on the short arm of chromosome 6 at region 6p21.
Question 2: Which HLA class II loci are considered the most polymorphic and clinically significant for transplantation?
- HLA-DRB1 and HLA-DQB1 (Correct answer)
- HLA-DPA1 and HLA-DPB1
- HLA-DMA and HLA-DMB
- HLA-DOA and HLA-DOB
Correct answer: HLA-DRB1 and HLA-DQB1
HLA-DRB1 and HLA-DQB1 are the most polymorphic class II loci and are routinely typed for solid organ transplantation.
Question 3: What term describes the tendency of certain HLA alleles to occur together on the same chromosome more often than expected by chance?
- Linkage disequilibrium (Correct answer)
- Codominant expression
- Haplotype shuffling
- Allelic exclusion
Correct answer: Linkage disequilibrium
Linkage disequilibrium describes the non-random association of alleles at two or more loci on the same chromosome within a population.
Question 4: HLA molecules are encoded by genes in which genomic region?
- Major Histocompatibility Complex (MHC) (Correct answer)
- T-cell receptor locus
- Immunoglobulin heavy chain locus
- Complement gene cluster
Correct answer: Major Histocompatibility Complex (MHC)
HLA molecules are encoded by genes within the MHC, which spans approximately 4 Mb on chromosome 6p21.
Question 5: Which feature of HLA class I molecules allows them to present endogenous peptides?
- Peptide-binding groove formed by alpha-1 and alpha-2 domains (Correct answer)
- Peptide-binding groove formed by alpha-1 and beta-1 domains
- Transmembrane domain complexed with beta-2 microglobulin
- Variable CDR3 loop structure
Correct answer: Peptide-binding groove formed by alpha-1 and alpha-2 domains
HLA class I molecules have a peptide-binding groove formed by the alpha-1 and alpha-2 domains of the heavy chain that accommodates 8–10 amino acid peptides.
Question 6: What is the inheritance pattern of HLA haplotypes?
- Codominant Mendelian inheritance as a haplotype unit (Correct answer)
- X-linked dominant
- Autosomal recessive only
- Mitochondrial inheritance
Correct answer: Codominant Mendelian inheritance as a haplotype unit
HLA haplotypes are inherited as a unit from each parent in a codominant Mendelian fashion, so children express alleles from both parents.
CHT HLA Genetics & Molecular Biology 1
Which chromosome carries the HLA gene complex in humans?