USMLE Step 1 Genetics Exam Questions with Correct Answers

co-dominance examples - Answer-blood groups a-1 antitrypsin deficiency variable expressivity example - Answer-NF1 incomplete penetrance example - Answer-BRCA1 mutations don't always result in breast/ovarian cancer pleiotropy: definition and example - Answer-one gene contributes to multiple effects example: PKU mosaicism - Answer-presence of genetically distinct cell lines in the same individual McCune-Albright Syndrome - Answer-due to mutation affecting G-protein signaling unilateral cafe-au-lait spots, polyostotic fibrous dysplasia, precocious puberty, multiple endocrine abnormalities lethal if mutation occurs before fertilization due to genetic mosaicism locus heterogeneity example - Answer-albinism allelic heterogeneity example - Answer-B-thalassemia heteroplasmy - Answer-presence of both normal and mutated tDNA, resulting in variable expression in mitochondrially inherited disease heterodisomy - Answer-uniparental disomy due to meiosis I error isodisomy - Answer-uniparental disomy due to meiosis II error chromosome affected by angel man and prader-willi disease - Answer-chromosome 15 MELAS Syndrome - Answer-mitochondrial inheritance mitochondrial encephalopathy, lactic acidosis, stroke like episodes general features of mitochondrial myopathies - Answer-myopathy, lactic acidosis, CNS disease x-linked dominant disease example - Answer-hypophosphatemic rickets list the x-linked recessive disorders - Answer-ornithine transcarbamylase deficiency