ABMGG ABMGG Molecular Genetics and Genomics Techniques 2 — Questions and Answers
Question 1: What does fluorescence in situ hybridization (FISH) detect that a standard G-banded karyotype typically cannot?
- Submicroscopic deletions at specific loci (Correct answer)
- Whole chromosome aneuploidy
- Large chromosomal translocations
- Polyploidy
Correct answer: Submicroscopic deletions at specific loci
FISH uses labeled probes to detect deletions or duplications at targeted loci below the ~5–10 Mb resolution of conventional karyotyping.
Question 2: Which sequencing methodology is used to detect epigenetic modifications such as DNA methylation patterns relevant to imprinting disorders?
- Bisulfite sequencing (Correct answer)
- Sanger sequencing
- Short-read whole exome sequencing
- SNP array
Correct answer: Bisulfite sequencing
Bisulfite treatment converts unmethylated cytosines to uracil while leaving methylated cytosines intact, enabling methylation mapping by sequencing.
Question 3: RNA sequencing (RNA-seq) adds clinical value in medical genetics primarily by:
- Identifying splicing defects and allele-specific expression abnormalities (Correct answer)
- Detecting copy number variants with higher resolution than CMA
- Replacing whole genome sequencing for SNV detection
- Measuring protein levels directly
Correct answer: Identifying splicing defects and allele-specific expression abnormalities
RNA-seq can reveal aberrant splicing caused by deep intronic variants and confirm whether a variant affects gene expression, increasing diagnostic yield.
Question 4: In the context of ABMGG laboratory practice, what is a mosaic variant?
- A variant present in only a subset of an individual's cells (Correct answer)
- A de novo variant found in both parents
- A benign polymorphism present in >1% of the population
- A variant spanning two different chromosomes
Correct answer: A variant present in only a subset of an individual's cells
Mosaicism arises when a post-zygotic mutation occurs in a progenitor cell, resulting in two or more genetically distinct cell populations within the same individual.
Question 5: Which term describes a variant that arose newly in a patient and is not present in either biological parent?
- De novo variant (Correct answer)
- Compound heterozygous variant
- Hemizygous variant
- Synonymous variant
Correct answer: De novo variant
A de novo variant occurs as a new mutation in the proband and is confirmed by demonstrating its absence in both parents via trio sequencing or targeted testing.
Question 6: Long-read sequencing technologies (e.g., PacBio, Oxford Nanopore) offer a key advantage over short-read platforms for clinical genomics because they:
- Can span repetitive regions and resolve complex structural variants (Correct answer)
- Provide lower error rates per base than short reads
- Are less expensive per gigabase than Illumina sequencing
- Require less DNA input than short-read platforms
Correct answer: Can span repetitive regions and resolve complex structural variants
Long reads can traverse repetitive DNA, phasing variants and characterizing structural rearrangements that short reads cannot span.
ABMGG ABMGG Molecular Genetics and Genomics Techniques 2
What does fluorescence in situ hybridization (FISH) detect that a standard G-banded karyotype typically cannot?