ABMGG Cytogenetics and Chromosomal Analysis

Question 1

Which banding technique is most commonly used to produce a standard karyotype in clinical cytogenetics laboratories?

Accepted Answer

G-banding

Answer

G-banding (Giemsa banding) is the standard technique used in clinical cytogenetics to produce a karyotype with characteristic dark and light band patterns.

Question 2

According to the ISCN (International System for Human Cytogenomic Nomenclature), how is a male with trisomy 21 correctly written?

Accepted Answer

47,XY,+21

Answer

47,XY,+21 indicates a male (XY) with 47 total chromosomes due to an extra chromosome 21, which is the correct ISCN notation for Down syndrome in a male.

Question 3

Fluorescence in situ hybridization (FISH) is best suited for detecting which type of chromosomal abnormality?

Accepted Answer

Submicroscopic deletions at targeted loci

Answer

FISH uses locus-specific probes to detect submicroscopic deletions or duplications at targeted regions that are too small to be seen by conventional karyotyping.

Question 4

A chromosomal microarray (CMA) using SNP probes has an advantage over array CGH in that it can detect:

Accepted Answer

Uniparental disomy (UPD)

Answer

SNP-based arrays can identify stretches of homozygosity that indicate uniparental disomy, which array CGH cannot detect because UPD does not involve copy number change.

Question 5

The most common cause of trisomy 21 (Down syndrome) is:

Accepted Answer

Meiotic nondisjunction

Answer

Approximately 95% of Down syndrome cases result from meiotic nondisjunction, most often in maternal meiosis I, leading to a gamete with two copies of chromosome 21.

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