Bacteria and other microbes can be used to "clean up" an oil spill by breaking down oil into carbon dioxide and water. Two samples isolated from the Deepwater Horizon leak in the Gulf of Mexico were labeled A and B. The DNA of each was isolated and the percent thymine measured in each sample. Sample A contains 17.7 17.7 % thymine and sample B contains 28.9 28.9 % thymine. Assume the organisms contain normal double‑stranded DNA and predict the composition of the other bases.

The composition of nitrogenous bases in DNA is calculated using the suggestions proposed by the results of the experiment performed by Erwin Chargaff.

He found that in a DNA sample the composition of purine to pyrimidine is 1:1. This indicates that the amount of purine equals pyrimidine. This can be presented as purines + pyrimidines= 100. Also, adenine binds thymine and cytosine binds guanine.

In the given question,

For sample A

A= 17.7 %, Therefore, thymine will be = 17.7 %,

A+T= 35.40%

Now, G+C=100- 35.40%

G+C= 64.60%

content of G= 64.60/2= 32.30%

content of C= 32.30%

For sample B

T=28.9%, A will be= 28.9%

A+T= 57.80%

G+C=100-57.80%

G+C= 42.20%

Thus content of G will be= 42.20/2=21.10

content of C= 21.10%

Thus,

For sample A, A=17.7 %, T=17.7 %, G=32.30%, C=32.30%

For sample B, A= 28.9%, T=28.9%, G= 21.10%, C= 21.10%