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Which of the following observations is the strongest evidence for an important genetic component in the causation of type-1 diabetes mellitus (IDDM)?
A Pancreatic b-cell autoantibodies are frequently present.
B Approximately 10% of affected indivifuals have an affected sibling.
C Onset of disease is usually in childhood.
D The concordance rate in monozygotic twins is approximately 30%.
E The concordance rate in monozygotic twins is five times that in dizygotic twins.

d or e

E

is stronger for genetics

EEE
Remember that monozygotic (MZ) twins have identical genotypes and dizygotic (DZ) twins share only 50% of their genetic information. Therefore if a trait is non-genetically determined then there should be no difference in the concordance rate (how often members of a twin pair show the same phenotype) between MZ and DZ twin pairs. If a trait has a genetic component then the rate of concordance is expected to be higher in MZ twins then in DZ twins.