Does the distribution of bases in sea urchin dna and salmon dna follow chargaff’s rules? a) yes, because the %a approximately equals the %t and the %g approximately equals the %c in both species. b) no, because %a + %t does not equal %g + %c in both species. c) no, because %a is higher than %t, and %g is higher than %c in both species. d) yes, because the %a + %t is greater than the %g + %c in both species.

A. Yes, because the %A approximately equals the %T and the %G approximately equals the %C in both species.

Explanation:

According to Chargaff's rule, in all cellular DNAs, the number of adenosine residues (A) is equal to the number of thymidine residues (T). And the number of guanosine residues (G) is equal to the number of cytidine residues (C). Therefore, the sum of the purine residues equals the sum of the pyrimidine residues (A+ G= C+ T). It is based on the fact that a purine base always pairs with a pyrimidine base in a double helix DNA.

Chargaff’s rule is followed in all the double-helical DNA molecules irrespective of the species. In DNAs of sea urchin and salmon, the percentage of adenine is equal to that of the thymine and the percentage of guanine is equal to that of the cytosine. Therefore, Chargaff's rule is followed.

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