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Biology · Grades 9–12

DNA base-percentage model

In the stated double-stranded DNA model, A = T and C = G; all four percentages sum to 100.

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Rule and assumptions

In the stated double-stranded DNA model, A = T and C = G; all four percentages sum to 100.

G% = (100 − 2A%)/2

Worked examples

In a canonical double-stranded DNA sample, adenine is 32% of all bases. Find the guanine percentage, assuming A = T and C = G. Round to 3 decimal places if needed. Answer in %.

G% = (100 − 2A%)/2 (100 − 2 × 32)/2 = 18

18 %

In a canonical double-stranded DNA sample, adenine is 18% of all bases. Find the guanine percentage, assuming A = T and C = G. Round to 3 decimal places if needed. Answer in %.

G% = (100 − 2A%)/2 (100 − 2 × 18)/2 = 32

32 %

Try two questions

  1. In a canonical double-stranded DNA sample, adenine is 23% of all bases. Find the guanine percentage, assuming A = T and C = G. Round to 3 decimal places if needed. Answer in %.

  2. In a canonical double-stranded DNA sample, adenine is 21% of all bases. Find the guanine percentage, assuming A = T and C = G. Round to 3 decimal places if needed. Answer in %.

Answers and reasoning

Answers and marking notes
  1. 27 %

    G% = (100 − 2A%)/2 (100 − 2 × 23)/2 = 27

  2. 29 %

    G% = (100 − 2A%)/2 (100 − 2 × 21)/2 = 29

Further reading and review references

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Learning preview · independent educational and translation review required. Suggested grades are not official curriculum alignment.