ASCP Molecular Diagnostics 3

Question 1

Reverse transcriptase PCR (RT-PCR) begins with which enzymatic step?

Accepted Answer

Conversion of mRNA to complementary DNA (cDNA) by reverse transcriptase

Answer

RT-PCR first uses reverse transcriptase (RNA-dependent DNA polymerase) to synthesize cDNA from an mRNA template. The resulting cDNA then serves as the template for standard PCR amplification.

Question 2

Loss of heterozygosity (LOH) at a tumor suppressor gene locus typically indicates:

Accepted Answer

Deletion or mitotic recombination eliminating the wild-type allele

Answer

LOH occurs when the remaining wild-type allele of a tumor suppressor gene is lost through deletion, uniparental disomy, or mitotic recombination, leaving only the mutant allele — fulfilling Knudson's two-hit hypothesis for cancer development.

Question 3

Which oncogene mutation is found in more than 90% of pancreatic adenocarcinomas?

Accepted Answer

KRAS (most commonly G12D)

Answer

KRAS mutations (predominantly G12D, G12V, and G12R) are found in more than 90% of pancreatic ductal adenocarcinomas (PDAC). KRAS encodes a GTPase; mutations lock it in the GTP-bound active form, driving continuous proliferative signaling.

Question 4

The International Sensitivity Index (ISI) is used to calculate the INR. What is its purpose?

Accepted Answer

To standardize PT results across different laboratories using different thromboplastin reagents

Answer

Different thromboplastin reagents vary in sensitivity to reductions in vitamin K-dependent factors. The ISI calibrates each reagent against an international reference; the INR formula [INR = (PT patient/PT normal) to the power of ISI] normalizes results so warfarin monitoring is comparable across labs.

Question 5

Which molecular technique provides the highest resolution for HLA allele-level typing?

Accepted Answer

Next-generation sequencing (NGS)

Answer

NGS provides the highest resolution allele-level HLA typing by generating phased sequence data, resolving ambiguities that arise with SSO, SSP, or Sanger sequencing. It is becoming the standard for unrelated donor searches in hematopoietic stem cell transplantation.

ASCP Practice Test

ASCP Practice Test

ASCP Molecular Diagnostics 3