Molecular Biology/Genetics USMLE Step 1 Practice Questions
58 board-style USMLE Step 1 questions in Biochemistry. Each question shows the correct answer; create a free account for the full explanation and adaptive practice.
- USMLE Step 1 · medium25. A 25-year-old male presents with red-green color blindness. Population screening reveals an allele frequency of color blindness in males at 1 in 100. Genetic testing confirms X-…
- USMLE Step 1 · medium26. A woman whose brother has cystic fibrosis seeks genetic counseling. She is told that she, her brother, and other family members can be tested for the common mutations known to c…
- USMLE Step 1 · medium27. A 20-year-old male presents with progressive weakness and myotonia, most pronounced in the hands and feet. Vital signs show HR 78/min, BP 118/76 mmHg, RR 14/min. Serum creatine…
- USMLE Step 1 · medium28. A 20-week gestation fetus is delivered after spontaneous abortion. Physical examination reveals microcephaly, microphthalmia, cleft lip and palate, polydactyly (six fingers bila…
- USMLE Step 1 · medium29. A scientist exposes a culture of a bacterium with minimal nutritional requirements to a chemical mutagen, then streaks out the bacteria on plates filled with a complex medium su…
- USMLE Step 1 · medium30. A 10-year-old female is admitted to the hospital because of a recurrent neurologic disorder. Her right arm and leg have become limp, and she is found to have lactic acidosis. Tw…
- USMLE Step 1 · medium31. A 32-year-old man with autosomal recessive inheritance disorder (prevalence 1/40,000) presents with progressive neurologic decline. Physical examination reveals BP 118/76, HR 88…
- USMLE Step 1 · medium32. RNA is isolated from the rough endoplasmic reticulum of several tissues, subjected to electrophoresis, blotted, and probed with a 32P-cDNA. The results from the autoradiogram ar…
- USMLE Step 1 · medium33. A 25-year-old male and his wife go to a fertility clinic for evaluation. His wife has no significant past medical history and is given a 'clean bill of health.' He has had bronc…
- USMLE Step 1 · medium34. A 2-year-old boy presents to the emergency department with gross hematuria and a palpable right abdominal mass. Vital signs reveal blood pressure of 128/82 mmHg (>95th percentil…
- USMLE Step 1 · medium35. A 2-year-old obese female has been diagnosed with Prader-Willi syndrome. To confirm the diagnosis, a DNA methylation assay is performed. A sample of her DNA is first cut with Ec…
- USMLE Step 1 · medium36. DNA, extracted from a patient, is to be tested by PCR and DNA sequencing to ascertain the presence of a particular mutation. The DNA sequence to be amplified by PCR is shown bel…
- USMLE Step 1 · medium37. A family is afflicted with a form of degenerative muscle disease. All members of the family represented by the pedigree have undergone PCR-based DNA testing, as shown. Based upo…
- USMLE Step 1 · medium38. In the family shown below, individuals affected with profound deafness are represented by a shaded symbol. (Pedigree shows two couples in generation I and II with normal hearing…
- USMLE Step 1 · medium39. A family has a history of genetic disease with an autosomal dominant pattern of inheritance. DNA from the grandfather (who is heterozygous for the disease) is cloned and used to…
- USMLE Step 1 · medium40. A 45-year-old male is diagnosed with cancer of the proximal portion of the colon. His father died of colon cancer at the age of 52. He has 3 siblings. His 55-year-old brother ha…
- USMLE Step 1 · medium41. Pseudogenes are homologues of functional genes that lack promoters and are therefore part of the unexpressed DNA. It is thought that at least some of these pseudogenes were prod…
- USMLE Step 1 · medium42. A 28-year-old white female and her 25-year-old white male partner present for genetic counseling. Both have one sibling with cystic fibrosis confirmed by sweat chloride testing…
- USMLE Step 1 · medium43. A gene product thought to be involved in the down-regulation of fetal hemoglobin expression is being investigated. Samples of primary tissue cultures of fetal, neonatal, and adu…
- USMLE Step 1 · medium44. When a cloned DNA fragment is used as a probe, a restriction fragment length polymorphism (RFLP) is revealed in the region adjacent to the centromere of chromosome 21. Four hapl…
- USMLE Step 1 · medium45. Police are investigating the case of a missing mother of 4 children. All 4 children have the same biological father. Single-locus short tandem repeat (STR) analysis was performe…
- USMLE Step 1 · medium46. On physical examination, a newborn is found to have micrognathia, a prominent occiput, low-set ears, and rocker-bottom feet. There is very little mental development during the f…
- USMLE Step 1 · medium47. A 5-year-old, intellectually impaired male is brought to the city from a rural community for evaluation. A careful history reveals intellectual impairment in a number of other f…
- USMLE Step 1 · medium48. A 45-year-old microbiologist studies a bacterial mutant with a lethal defect preventing chromosome replication. The organism shows BP 120/80, HR 78, RR 16, Temp 37°C. DNA analys…