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GATE 2023 BT – Question 55

Genetics, Cellular and Molecular Biology · Molecular Biology: Structure of genes and chromosomes, mutations and mutagenesis, regulation of gene expression · 2 marks · Numerical answer

DNA sample collected from an unidentified bacterial species (Y) contains 13% of adenine. The G+C content (in percentage) of Y is ___________.

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Correct answer: 74

Explanation

**Chargaff's rules** for double-stranded DNA: $A=T$ and $G=C$.

**Step 1:** $A=13\%$, so $T=13\%$ and $A+T=26\%$.

**Step 2:** the rest is $G+C$:
$$G+C=100-26=\mathbf{74\%}.$$