Detecting Alzheimer’s disease at an early age. Geneticists at Australian National University are studying whether the cognitive effects of Alzheimer’s disease can be detected at an early age (Neuropsychology, Jan. 2007). One portion of the study focused on a particular strand of DNA extracted from each in a sample of 2,097 young adults between the ages of 20 and 24. The DNA strand was classified into one of three genotypes: E4 + >E4 +, E4 + >E4 - , and E4 - >E4 - .

The number of young adults with each genotype is shown in the table. Suppose that in adults who are not afflicted with Alzheimer’s disease, the distribution of genotypes for this strand of DNA is 2% with E4 + >E4 +, 25% with E4 + >E4 - , and 73% with E4 - >E4 - . If differences in this distribution are detected, then this strand of DNA could lead researchers to an early test for the onset of Alzheimer’s. Conduct a test (at a = .05) to determine if the distribution of E4/E4 genotypes for the population of young adults differs from the norm.

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Genotype: E4/E4 E4/E4 E4/E4 Number of young adults: 56 517 1,524