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What is the primary purpose of G-banding in conventional cytogenetic analysis?

To identify single nucleotide variants in coding regions

To produce a reproducible banding pattern for chromosome identification and structural analysis

To quantify gene expression levels across the genome

To detect methylation patterns at CpG islands

to track

2026 Statistics

Key Facts: ABMGG LGG Exam

150

Specialty Exam Questions

Three 50-item blocks

100

General Exam Questions

Two 50-item blocks

53%

Applications & Interpretation

Largest content domain

$2,850

Total Exam Fees

Application + general + specialty

2 years

Fellowship Required

ACGME-accredited LGG program

Annual

Exam Frequency

August testing window

The LGG certification requires passing both a 100-item general exam and a 150-item specialty exam during the same testing cycle (August 2026). The specialty exam covers 5 domains: Applications & Interpretation (53%), Pathogenesis (20%), Normal Structure & Function (10%), Nomenclature (10%), and Laboratory Management (7%). Exams are administered at Pearson VUE test centers. Candidates must hold an MD, DO, or PhD and complete a 2-year ACGME-accredited LGG fellowship.

Sample ABMGG LGG Practice Questions

Try these sample questions to test your ABMGG LGG exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1What is the primary purpose of G-banding in conventional cytogenetic analysis?

A.To identify single nucleotide variants in coding regions

B.To produce a reproducible banding pattern for chromosome identification and structural analysis

C.To quantify gene expression levels across the genome

D.To detect methylation patterns at CpG islands

Explanation: G-banding (Giemsa banding) uses trypsin digestion followed by Giemsa staining to produce a characteristic light and dark banding pattern on metaphase chromosomes. This reproducible banding pattern allows cytogeneticists to identify each chromosome pair and detect numerical and structural abnormalities such as translocations, deletions, inversions, and duplications. G-banding has a resolution of approximately 5-10 Mb and remains the standard first-line cytogenetic test for constitutional and acquired chromosomal abnormalities.

2A karyotype shows 45,X in 80% of cells and 46,XX in 20% of cells from peripheral blood. How should this result be reported using ISCN nomenclature?

A.45,X/46,XX

B.mos 45,X[80]/46,XX[20]

C.45,X[80%]/46,XX[20%]

D.46,XX/45,X

Explanation: Under ISCN conventions, mosaic karyotypes are designated with 'mos' preceding the clone descriptions. Each cell line is listed with its chromosome complement followed by the number of cells observed in square brackets. The abnormal clone is listed first. The correct designation is mos 45,X[80]/46,XX[20], indicating that 80 cells had monosomy X and 20 cells had a normal female karyotype. Percentages are not used in the cell count brackets, and the 'mos' prefix explicitly indicates mosaicism.

3Which technique is MOST appropriate for rapidly confirming a suspected diagnosis of trisomy 21 in a neonate before full karyotype results are available?

A.Whole genome sequencing

B.Interphase FISH with chromosome 21-specific probes

C.Southern blot analysis

D.Sanger sequencing of the DYRK1A gene

Explanation: Interphase FISH (fluorescence in situ hybridization) using locus-specific probes for chromosome 21 provides rapid results (typically within 24-48 hours) without the need for cell culture. By counting the number of signals in interphase nuclei, a third signal for chromosome 21 confirms trisomy 21. This is far faster than conventional karyotyping (7-14 days) and more targeted than whole genome sequencing. Southern blot and Sanger sequencing are not appropriate for aneuploidy detection.

4A chromosomal microarray (CMA) reveals a 3 Mb deletion at 22q11.2 in a child with conotruncal heart defect and palatal abnormalities. What is the most likely diagnosis?

A.Williams syndrome

B.DiGeorge syndrome / 22q11.2 deletion syndrome

C.Angelman syndrome

D.Smith-Magenis syndrome

Explanation: A 3 Mb deletion at 22q11.2 is the hallmark finding in DiGeorge syndrome (22q11.2 deletion syndrome), which presents with conotruncal heart defects (e.g., tetralogy of Fallot, interrupted aortic arch), palatal abnormalities, immune deficiency, and hypocalcemia. Williams syndrome involves a 7q11.23 deletion, Angelman syndrome involves a 15q11.2 deletion (maternal), and Smith-Magenis syndrome involves a 17p11.2 deletion. CMA can detect submicroscopic deletions and duplications below the resolution of conventional karyotyping.

5In the ACMG/AMP 5-tier variant classification system, which category indicates that there is strong evidence supporting a causative role in disease?

A.Likely benign

B.Variant of uncertain significance (VUS)

C.Likely pathogenic

D.Pathogenic

Explanation: The ACMG/AMP 5-tier classification system categorizes variants as: Pathogenic, Likely Pathogenic, Variant of Uncertain Significance (VUS), Likely Benign, or Benign. The 'Pathogenic' classification indicates strong evidence (greater than 99% certainty) that the variant is disease-causing, based on criteria including population data, computational/predictive data, functional data, and segregation data. 'Likely Pathogenic' indicates greater than 90% certainty. The distinction is clinically important as only Pathogenic and Likely Pathogenic variants should be used for clinical decision-making.

6What is the resolution limit of standard G-banded karyotype analysis?

A.50-100 kb

B.1-2 Mb

C.5-10 Mb

D.50-100 Mb

Explanation: Standard G-banded karyotype analysis has a resolution of approximately 5-10 Mb (megabases), meaning deletions, duplications, or rearrangements smaller than this cannot be reliably detected. High-resolution banding with extended chromosomes can improve resolution to approximately 3-5 Mb. For detection of smaller copy number variants, techniques such as FISH (100 kb-1 Mb), chromosomal microarray (20-100 kb), or next-generation sequencing are required.

7Which FISH probe strategy would be MOST useful for detecting a BCR-ABL1 fusion gene in chronic myeloid leukemia?

A.Centromeric enumeration probes for chromosomes 9 and 22

B.Dual-color, dual-fusion probes targeting BCR and ABL1

C.Whole chromosome painting probes for chromosome 22

D.Telomeric probes for the long arms of chromosomes 9 and 22

Explanation: Dual-color, dual-fusion (D-FISH) probes are the optimal strategy for detecting BCR-ABL1 fusion in CML. One probe (e.g., red) spans the BCR gene on chromosome 22 and another probe (e.g., green) spans the ABL1 gene on chromosome 9. In a normal cell, there are two separate red and two separate green signals. In a cell with t(9;22), the fusion produces two yellow (overlapping red/green) signals from both the der(9) and der(22) chromosomes. This strategy reduces false-positive rates compared to single-fusion probe designs.

8During SNP array analysis, contiguous stretches of homozygosity (ROH) across multiple chromosomes are identified. What is the most likely explanation?

A.Technical artifact from poor DNA quality

B.Consanguinity in the parents

C.Uniparental disomy of a single chromosome

D.Somatic mosaicism for a balanced translocation

Explanation: Regions of homozygosity (ROH) distributed across multiple chromosomes are characteristic of consanguinity (parental relatedness). The extent and number of ROH segments correlate with the degree of relatedness. In contrast, uniparental disomy (UPD) typically produces ROH on a single chromosome. Identity-by-descent segments from consanguinity increase the risk of autosomal recessive disorders. SNP arrays are particularly useful for detecting ROH because they genotype millions of SNPs across the genome.

9What is the primary advantage of array comparative genomic hybridization (aCGH) over conventional karyotyping?

A.Ability to detect balanced translocations

B.Higher resolution for detecting submicroscopic copy number variants

C.Ability to assess cell culture viability

D.Detection of low-level mosaicism below 5%

Explanation: Array CGH (aCGH) has significantly higher resolution than conventional karyotyping, capable of detecting copy number variants as small as 20-100 kb compared to the 5-10 Mb resolution of G-banding. This allows detection of submicroscopic deletions and duplications causing microdeletion/microduplication syndromes. However, aCGH cannot detect balanced rearrangements (translocations, inversions) since there is no net gain or loss of material. It also has limited sensitivity for low-level mosaicism compared to karyotyping, typically requiring at least 15-20% abnormal cells.

10A laboratory receives an amniotic fluid specimen for prenatal chromosomal microarray analysis. Which finding would require parental studies for proper interpretation?

A.Trisomy 21

B.A 47,XXY karyotype

C.A 500 kb deletion classified as a variant of uncertain significance

D.Normal female result, arr(1-22)x2,(X)x2

Explanation: A copy number variant (CNV) classified as a variant of uncertain significance (VUS) requires parental studies (trio analysis) to determine whether the variant is de novo or inherited. A de novo CNV is more likely to be clinically significant, while an inherited CNV from a healthy parent may be benign. Trisomy 21 and 47,XXY are well-characterized aneuploidies with established clinical significance that do not require parental studies for interpretation. A normal result requires no follow-up.

About the ABMGG LGG Exam

The ABMGG Laboratory Genetics and Genomics (LGG) certification is a doctoral-level board credential for laboratory geneticists who direct and interpret clinical cytogenetic and molecular genetic analyses. Diplomates are qualified to serve as laboratory directors under CLIA and consult on diagnosis and management of inherited and acquired genetic disorders.

Questions

150 scored questions

Time Limit

3 hours (three 60-minute blocks)

Passing Score

Criterion-referenced (not publicly disclosed)

Exam Fee

~$2,850 total (application + general + specialty exam) (American Board of Medical Genetics and Genomics (ABMGG))

ABMGG LGG Exam Content Outline

53%

Applications and Interpretation

Core laboratory techniques (FISH, microarray, NGS, Sanger, PCR), diagnosis of symptomatic individuals, predictive/carrier testing, prenatal screening, tumor genomics, pharmacogenomics, and bioinformatics

20%

Pathogenesis

Nondisjunction, structural aberrations, mosaicism, triplet expansion, single nucleotide variants, imprinting/methylation, LOH/UPD, microsatellite instability, mitochondrial mutations

10%

Normal Structure and Function

Chromosome structure, genome organization, mitosis/meiosis, cell cycle, DNA/RNA structure, gene mapping, transcription/translation, X-inactivation

10%

Nomenclature

ISCN cytogenetic nomenclature (2024 edition), HGVS molecular nomenclature for sequence variants, standard reporting conventions

Laboratory Management

Quality assurance/quality control, CAP/CLIA regulations, proficiency testing, assay validation, personnel qualifications, laboratory accreditation

How to Pass the ABMGG LGG Exam

What You Need to Know

Passing score: Criterion-referenced (not publicly disclosed)
Exam length: 150 questions
Time limit: 3 hours (three 60-minute blocks)
Exam fee: ~$2,850 total (application + general + specialty exam)

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

ABMGG LGG Study Tips from Top Performers

1Prioritize the Applications and Interpretation domain (53% of the exam) — master FISH, microarray, NGS workflows, PCR methods, and variant classification

2Know ISCN 2024 nomenclature thoroughly for describing karyotypes, FISH results, and microarray findings

3Study HGVS nomenclature for describing sequence variants at the DNA, RNA, and protein levels

4Review ACMG/AMP 5-tier variant classification criteria (pathogenic, likely pathogenic, VUS, likely benign, benign)

5Understand CAP/CLIA laboratory regulations, proficiency testing requirements, and assay validation parameters

6Practice interpreting cytogenetic cases including complex karyotypes, mosaicism, and structural rearrangements

7Study NGS bioinformatics pipelines from library prep through variant calling, annotation, and filtering

8Review prenatal testing methods including NIPT, amniocentesis, CVS, and PGT indications and limitations

Frequently Asked Questions

What is the ABMGG LGG certification?

The ABMGG Laboratory Genetics and Genomics (LGG) certification is a doctoral-level board credential offered by the American Board of Medical Genetics and Genomics. It certifies competence in directing and interpreting clinical cytogenetic and molecular genetic analyses for diagnosis and management of inherited and acquired genetic disorders. LGG diplomates are qualified to serve as CLIA laboratory directors.

How many questions are on the ABMGG LGG exam?

The LGG specialty exam has 150 items split into three blocks of 50 questions, with 60 minutes per block and 10-minute breaks between blocks. Candidates must also pass the 100-item general exam (two blocks of 50 questions). Both exams must be passed during the same testing cycle.

What are the prerequisites for the ABMGG LGG exam?

Candidates must hold a doctoral degree (MD, DO, or PhD in genetics, genomics, human genetics, or a related biological science) and complete a 2-year ACGME-accredited laboratory genetics postdoctoral training fellowship. A 200-case logbook documenting cytogenetic and molecular laboratory experience must also be submitted.

What topics are covered on the ABMGG LGG exam?

The five content domains are: Applications and Interpretation (53%) covering lab techniques like FISH, microarray, NGS, and PCR; Pathogenesis (20%) covering mechanisms of genetic disease; Normal Structure and Function (10%); Nomenclature (10%) using ISCN 2024 and HGVS standards; and Laboratory Management (7%) covering QA/QC, CAP/CLIA, and proficiency testing.

How much does the ABMGG LGG certification cost?

Total fees are approximately $2,850: application review fee (~$750), general examination fee (~$1,000), and specialty examination fee (~$1,100). A late application fee of $400 applies after the January 15 deadline. Credit card payments incur a 3% processing fee; ACH payments have no additional fee.

When is the ABMGG LGG exam offered?

The ABMGG certification exams are offered annually in August. The 2026 exam dates are August 12-15, 2026. Exams are administered at Pearson VUE test centers worldwide. Candidates must complete training by July 31 of the exam year.

What is the passing score for the ABMGG LGG exam?

The ABMGG uses a criterion-referenced passing standard that is not publicly disclosed as a specific percentage. The passing score is determined by subject matter experts using psychometric methods to ensure a minimum competency standard. Pass/fail results are typically released several weeks after the exam.

How should I prepare for the ABMGG LGG exam?

Focus study on the five content domains weighted by the official blueprint. The Applications and Interpretation domain (53%) should receive the most attention, covering techniques like NGS, FISH, microarray, and variant classification. Use the ABMGG content outline and learning guide, review ACMG/AMP variant classification guidelines, and practice with cytogenetic and molecular case interpretations.

What is the difference between the ABMGG general exam and the LGG specialty exam?

The general exam (100 items) tests broad medical genetics knowledge across all specialties including chromosomal inheritance, population genetics, cancer genetics, and genetic counseling principles. The LGG specialty exam (150 items) focuses specifically on laboratory techniques, molecular and cytogenetic analysis, variant interpretation, and lab management. Both must be passed in the same testing cycle for initial certification.