Light-to-dark transition of genes. Synechocystis, a type of cyanobacterium that can grow and survive in a wide range of conditions, is used by scientists to model DNA behavior. In the Journal of Bacteriology (July 2002), scientists isolated genes of the bacterium responsible for photosynthesis and respiration and investigated the sensitivity of the genes to light. Each gene sample was grown to midexponential phase in a growth incubator in ‘‘full light.'' The lights were extinguished and growth measured after 24 hours in the dark (‘‘full dark''). The lights were then turned back on for 90 minutes (‘‘transient light'') followed immediately by an additional 90 minutes in the dark (‘‘transient dark''). Standardized growth measurements in each light/dark condition were obtained for 103 genes. The complete data set is saved in the GENEDARK ?le. Data for the ?rst 10 genes are shown in the accompanying table.

(a) Treat the data for the ?rst 10 genes as a random sample collected from the population of 103 genes and test the hypothesis of no difference between the mean standardized growth of genes in the full-dark condition and genes in the transient light condition. Use α = .01.

(b) Use a statistical software package to compute the mean difference in standardized growth of the 103 genes in the full-dark condition and the transient-light condition. Did the test, part a, detect this difference?

(c) Repeat parts a and b for a comparison of the mean standardized growth of genes in the full-dark condition and genes in the transient-dark condition.

GENE ID              FULL-DARK            TR-LIGHT            TR-DARK

SLR2067           -0.00562                  1.40989          -1.28569

SLR1986           -0.68372                  1.83097          -0.68723

SSR3383           -0.25468               -0.79794          -0.39719

SLL0928           -0.18712               -1.20901          -1.18618

SLR0335           -0.20620                  1.71404          -0.73029

SLR1459           -0.53477                  2.14156          -0.33174

SLL1326           -0.06291                  1.03623                 0.30392

SLR1329           -0.85178               -0.21490             0.44545

SLL1327               0.63588                 1.42608         -0.13664

SLL1325           -0.69866             1.93104          -0.24820

Source: Gill, R. T., et al. ‘‘Genome-wide dynamic transcriptional pro?ling of the light to dark transition in Synechocystis Sp. PCC6803,'' Journal of Bacteriology, Vol. 184, No. 13, July 2002.

(d) Repeat parts a and b for a comparison of the mean standardized growth of genes in the transient-light condition and genes in the transient-dark condition.