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 19.3 % thymine and sample B contains 29.7 % thymine. Assume the organisms contain normal double‑stranded DNA and predict the composition of the other bases.

"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 19.3 % thymine and sample B contains 29.7 % thymine. Assume the organisms contain normal double‑stranded DNA and predict the composition of the other bases."

DNA is made up of four bases: Adenine (A), Thymine (T), Cytosine (C) and Guanine (G).

Adenine and Thymine are paired and are joined by two hydrogen bonds: A-T.
Cytosine and Guanine are paired and are joined by three hydrogen bonds: C-G.

If Sample A contains 19.3% thymine, therefore it contains the same percentage of adenine. Added together 19.3+19.3=38.6%.

Since A-T is 38.6%, therefore C-G is 100 - 38.6% = 61.4%

Dividing 61.4% in half, C and G are 30.7% each.

In summary, for Sample A:

Adenine = 19.3%

Thymine = 19.3%

Cytosine = 30.7%

Guanine = 30.7%

For Sample B, since thymine is 29.7%, adenine is also 29.7%

So A-T is 29.7 +29.7 = 59.4%

C-G = 100 - 59.4 = 40.6%

Dividing 40.6% in half, C and G are 20.3% each

In summary, for Sample B:

Adenine = 29.7%

Thymine = 29.7%

Cytosine = 20.3%

Guanine = 20.3%