Blood samples are usually stored in plates of 16 wells 36 we

Blood samples are usually stored in plates of 16 wells, 36 wells, or 100 wells (e.g., a 16-well plate contains 16 blood samples). These samples are genotyped (a process of translating a blood sample into DNA sequence data) in plates. The heterozygosity of a blood sample is a measurement that is used to determine whether the sample is contaminated or failed to genotype. An unusually large or small average heterozygosity of the blood samples in a plate is often indicative of genotyping error or blood sample contamination. When this happens, further inspection on the entire plate is required.

The heterozygosity of a typical (successfully genotyped) blood sample follows a distribution with the following characteristics (percentile abbreviated as pctl):

1st pctl

5th pctl

25th pctl

50th pctl

Mean

75th pctl

95th pctl

99th pctl

SD

0.26

0.30

0.34

0.35

0.35

0.36

0.40

0.44

0.03

1) A 16 well-plate was randomly selected. The average heterozygosity was calculated on the 16 blood samples in the plate. What would you expect the distribution of the average heterozygosity to look like? What would you expect if this is a 36 well-plate? A 100-well plate? Specify the mean, standard deviation, and the shape of the distribution. Justify your answer and make sure to state all assumptions. If you cannot come up with an answer, state so and briefly explain why not.

Solution

The blood samples does not follow the normal model, becuase the total probability exceeds unity.