2. If a double stranded DNA has 20 percent of cytosine, calculate the percent of adenine in the DNA.
By Chargaff's rule, we know that A=T and G=C. Since there are 20% cytosines, so guanines percentage will also be 20%. The G+C count is 20+20= 40%. Therefore, the remaining 60% will be contributed equally by adenine and thymine. Thus, the percentage of adenine and thymine is 30% each.