Single digests give: EcoRI = 6,000 (one fragment); BamHI = 4,000 + 2,000. The double digest gives 3,500 + 1,500 + 1,000.
Which arrangement of cut sites is most consistent with these data?
- A
Three BamHI sites only
- B
One BamHI and two EcoRI sites
- Ccheck_circle
Two BamHI sites and one EcoRI site, with EcoRI inside the 2,000-bp BamHI fragment splitting it into 1,000 + 1,000
- D
Two BamHI sites and one EcoRI site, with EcoRI inside the 4,000 fragment splitting it into 3,500 + 500
Explanation
The double digest shows the 4,000 fragment was split (3,500 + 500 doesn't appear, but 3,500 + 1,500 sums to 5,000 - inconsistent) - reconsidering: 3,500 + 1,500 = 5,000 from one BamHI fragment plus a 1,000 fragment. The pattern 3,500 + 1,500 + 1,000 totaling 6,000 is consistent with EcoRI cutting the 4,000-bp BamHI fragment into 3,500 + 500 plus the 2,000 fragment - matching is approximate; the key is that EcoRI cuts within one BamHI fragment, generating a third band.