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Genetics — Step 1 practice questions
105 questions in this area, with an explanation for every answer choice.
Three samples below, free and without an account.
How this shows up on Step 1
Inheritance patterns, pedigree interpretation, and the molecular basis of named conditions. Many questions are answerable from the pedigree alone. Population genetics appears often enough to be worth the small effort it takes to learn.
Sample questions
Sample question 1
A patient has hyperextensible, fragile skin, joint hypermobility, and easy bruising, with a defect in collagen synthesis. Which of the following is the most likely diagnosis?
Explanations
A. Marfan syndrome
Marfan syndrome results from a FIBRILLIN (not primarily collagen) defect, causing a different phenotype (tall stature, lens dislocation, aortic dilation) without this classic skin hyperextensibility/fragility pattern.
B. Osteogenesis imperfecta exclusively
Osteogenesis imperfecta also involves collagen defects but primarily manifests as bone fragility/fractures, not primarily this skin hyperextensibility pattern.
C. Down syndrome
Down syndrome is a chromosomal trisomy, unrelated to this collagen defect presentation.
D. Klinefelter syndrome
Klinefelter syndrome is a sex chromosome abnormality, unrelated to this collagen defect presentation.
E. Ehlers-Danlos syndrome · correct
Ehlers-Danlos syndrome, resulting from various collagen synthesis/structure defects, classically causes hyperextensible fragile skin, joint hypermobility, and easy bruising/poor wound healing.
Sample question 2
A child in a malaria-endemic region has a rapidly growing jaw mass. Biopsy shows a "starry sky" pattern with sheets of monotonous medium-sized cells. Cytogenetics reveal t(8;14). Which of the following is the most likely diagnosis?
Explanations
A. Mantle cell lymphoma
Mantle cell lymphoma shows t(11;14) with cyclin D1 overexpression, a different translocation and typically a different presentation.
B. Diffuse large B-cell lymphoma
DLBCL shows sheets of large atypical cells, without this specific translocation/starry sky/jaw mass combination as classically described for Burkitt.
C. Burkitt lymphoma · correct
The endemic (African) form of Burkitt lymphoma classically presents with a jaw mass, is associated with EBV infection (in malaria-endemic regions), shows the characteristic "starry sky" pattern (tingible body macrophages among monotonous lymphoma cells), and the t(8;14) translocation causing MYC overexpression.
D. Hodgkin lymphoma
Hodgkin lymphoma shows Reed-Sternberg cells, not this starry sky pattern.
E. Follicular lymphoma
Follicular lymphoma shows t(14;18) with BCL-2 overexpression and a nodular pattern, not this "starry sky" pattern or jaw mass presentation.
Sample question 3
Which of the following is the most common cytogenetic mechanism underlying Down syndrome?
Explanations
A. Meiotic nondisjunction resulting in trisomy 21 · correct
The vast majority (about 95%) of Down syndrome cases result from meiotic nondisjunction (typically maternal, with increasing risk with advanced maternal age), causing full trisomy 21.
B. Ring chromosome formation
Ring chromosome formation is a rare, unusual mechanism, not the most common cause of Down syndrome.
C. Robertsonian translocation
Robertsonian translocation is an important but less common cause of Down syndrome (accounting for a minority of cases), often associated with younger maternal age and familial recurrence risk.
D. Deletion of chromosome 21
Down syndrome results from an extra copy (trisomy), not a deletion, of chromosome 21.
E. Mosaicism exclusively
Mosaic Down syndrome is a less common variant (a small percentage of cases), not the most common mechanism.
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