USMLE STEP 1 GENETICS Questions and Answers with Complete Solutions 2024

USMLE STEP 1 GENETICS Questions and Answers with Complete Solutions 2024 Codominance - ANSNeither of the two alleles is dominant Contributions of both alleles are visible and one does not overpower the other completely ex) ABO blood type Variable expression - ANSNature and Severity of the phenotype vary between individuals given a particular genotype Incomplete penetrance - ANSNot all individuals with a mutant genotype show the phenotype Pleiotropy - ANSA particular gene has more than one effect on an individual's phenotype ex) PKU causes many seemingly unrelated symptoms Imprinting - ANSPhenomenon where certain genes are expressed in parent-of- origin specific manner Leads to differences in phenotype depending on whether the mutation is of maternal or paternal origin Anticipation - ANSSeverity of disases worsens OR age of onset is earlier in successive generations Loss of heterozygosity - ANSLoss of normal function of one allele of a gene in which the other allele was already defective (normal heterozygote -> mutant homozygote) Commonly seen with tumor suppressor genes and oncogenesis (two hit hypothesis); NOT the case with oncogenes (need only