Final answer:
According to Chargaff's rules, if a genome is 30% adenine, it is also 30% thymine, and the remaining 40% of the DNA is equally split between guanine and cytosine, resulting in 20% guanine.
Step-by-step explanation:
According to Chargaff's rules, the amount of adenine (A) found in double-stranded DNA is approximately equal to the amount of thymine (T), and the amount of guanine (G) is approximately equal to the amount of cytosine (C). Thus, if a genome is found to be 30% adenine, then we can conclude that it should also be 30% thymine since A pairs with T.
To find the percentage of guanine, we can use the fact that DNA consists of equal amounts of purines (A+G) and pyrimidines (T+C). Given that adenine and thymine together would make up 60% of the genome (30% A and 30% T), the remaining 40% would be equally divided between guanine and cytosine as per Chargaff's rules (G=C). Therefore, guanine would also represent 20% of the genome, the same as cytosine.