ABMGG Cytogenetics and Chromosomal Analysis 3

Question 1

A copy number variant (CNV) is generally defined as a segment of DNA greater than how many base pairs that shows variation in copy number relative to a reference genome?

Accepted Answer

1,000 bp (1 kb)

Answer

CNVs are conventionally defined as segments ≥1 kb (1,000 bp) that are present at variable copy numbers compared to a reference genome, distinguishing them from smaller insertion/deletion variants.

Question 2

Which prenatal cytogenetic technique provides the earliest diagnostic result for chromosomal abnormalities, typically performed at 10–13 weeks gestation?

Accepted Answer

Chorionic villus sampling (CVS)

Answer

CVS is performed at 10–13 weeks and provides fetal chromosomal material earlier than amniocentesis (15–20 weeks) or cordocentesis (18+ weeks).

Question 3

In cancer cytogenetics, a deletion of 17p13.1 is most associated with loss of function of which tumor suppressor gene?

Accepted Answer

TP53

Answer

TP53, which encodes the p53 tumor suppressor protein, is located at 17p13.1, and its deletion or mutation is one of the most common alterations across many cancers.

Question 4

Chromosomal instability syndromes such as Bloom syndrome, Fanconi anemia, and ataxia-telangiectasia share which cytogenetic hallmark?

Accepted Answer

Increased frequency of chromosomal breaks and rearrangements

Answer

These syndromes are caused by defects in DNA repair pathways, resulting in elevated rates of chromosomal breaks, sister chromatid exchanges, and structural rearrangements detectable cytogenetically.

Question 5

When reporting a Robertsonian translocation between chromosomes 13 and 14, the correct ISCN notation for a carrier with 45 chromosomes is:

Accepted Answer

45,XY,rob(13;14)(q10;q10)

Answer

ISCN uses rob() to denote Robertsonian translocations; 45,XY,rob(13;14)(q10;q10) correctly indicates a male carrier with 45 chromosomes due to fusion of acrocentric chromosomes 13 and 14 at their centromeres.

ABMGG - American Board of Medical Genetics and Genomics Practice Test

ABMGG - American Board of Medical Genetics and Genomics Practice Test

ABMGG Cytogenetics and Chromosomal Analysis 3