In DNA of certain organisms, guanine constitutes 20% of the bases. What percentage of the bases would be adenine?
a)	0%	b)	10%	c)	20%	d)	30%

(d)

According to Chargaff’s rule, in DNA, the proportion of adenine always equals to that of thymine and proportion of guanine always equal to that of cytosine, ., A=T and G=C. Thus, in a DNA, if guanine is 20%, cytosine also will be 20%. So, both adenine and thymine together will be 60%,  30% adenine and 30% thymine.