Calculating Adenine Percentage from GC Content

This question requires applying Chargaff's rules to determine the percentage of Adenine (A) in a DNA genome, given the Guanine-Cytosine (GC) content.

Understanding Chargaff's Rules

Chargaff's rules are fundamental principles of DNA composition:

• The percentage of Guanine (G) is equal to the percentage of Cytosine (C). ($G = C$)
• The percentage of Adenine (A) is equal to the percentage of Thymine (T). ($A = T$)
• The sum of all base percentages equals 100%. ($A + T + G + C = 100\%$)

Step-by-Step Calculation

1. Given GC Content: The genome has 60% GC content. This means the combined percentage of Guanine and Cytosine is 60%.
   $G + C = 60\%$

2. Calculate Individual G and C Percentages: Since $G = C$, we can find the percentage of each base by dividing the total GC content by 2.
   $G = C = \frac{60\%}{2} = 30\%$

3. Calculate Remaining Base Percentage (A + T): The total percentage of Adenine and Thymine is the remainder after accounting for GC content.
   $A + T = 100\% - (G + C)$
   $A + T = 100\% - 60\% = 40\%$

4. Calculate Adenine Percentage: According to Chargaff's rules, $A = T$. Therefore, we divide the combined percentage of A + T by 2 to find the percentage of Adenine.
   $A = \frac{A + T}{2}$
   $A = \frac{40\%}{2} = 20\%$

The percentage of Adenine (A) in this genome is 20%.