1) Identify Patterns
Pattern: Chargaff's rule states that in DNA, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). Looking at the data table, we can see that this rule is generally followed in all five organisms. The percentages of A and T are similar, as are the percentages of G and C.
2) Calculate
According to Chargaff's rule, if a species has 35 percent adenine in its DNA, then it must also have 35 percent thymine. This leaves 65 percent of the DNA for the other two bases, guanine and cytosine. Since the amount of guanine is equal to the amount of cytosine in DNA, each of these bases must make up half of the remaining 65 percent. Therefore, the percentage of guanine and cytosine in this hypothetical species would each be 32.5 percent.
3) Develop Models
The pattern in the data is useful for developing a model of DNA because it provides important information about the structure of the molecule. Specifically, Chargaff's rule tells us that the two strands of DNA are complementary, meaning that the sequence of nucleotide bases on one strand determines the sequence on the other strand. This is because adenine always pairs with thymine through two hydrogen bonds, while guanine always pairs with cytosine through three hydrogen bonds. This information has been crucial for understanding DNA replication and the transmission of genetic information from one generation to the next.
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