Question

results of dna replication
original dna strand
a. first round
1.
2.
b. second round
3.
4.
in the dna replication above, type the roman numeral of the image that would be placed in 4.
i
ii
iii
iv
none of the choices listed

Explanation:

DNA replication is semi - conservative, meaning each new DNA molecule consists of one original strand and one newly synthesized strand.

1. In the first round of replication (A), the original DNA strand (blue) will produce two DNA molecules: one with the original blue strand and a new yellow strand (let's say this is related to image II) and one with a new blue strand and the original yellow strand? Wait, no, looking at the left side: Image I has two yellow strands, Image II has one blue and one yellow, Image III has two blue strands.

1. The original DNA is blue (let's assume). First round (A): the two products (1 and 2) should be like Image II (one original, one new) and maybe Image... Wait, the original DNA is a double helix (blue). After first round of semi - conservative replication, each new DNA has one old (blue) and one new (yellow) strand, so like Image II. Then in the second round (B), the DNA with one blue and one yellow (from first round) will replicate again. The blue strand will make a new yellow strand, and the yellow strand will make a new blue strand? Wait, no, semi - conservative replication: each strand serves as a template. So the DNA molecule with one blue (original) and one yellow (new from first round) will, in the second round, produce two DNA molecules: one with blue (original) and new yellow, and one with yellow (old from first round) and new blue. But the DNA molecule that was all new yellow (if there was one? Wait, no, first round: original is blue - blue. After first round, we have blue - yellow (Image II) and blue - yellow? Wait, maybe the left images: Image I is yellow - yellow, Image II is blue - yellow, Image III is blue - blue.

Original DNA is Image III (blue - blue). First round (A) replication: each strand (blue) is a template. So we get two DNA molecules, each with one blue (original) and one yellow (new) strand, which is Image II. Then in the second round (B), each of these Image II (blue - yellow) DNA molecules will replicate. The blue strand will make a new yellow strand, and the yellow strand will make a new blue strand. So for the DNA molecule that was blue - yellow, after second round, we get one blue - yellow (from blue template) and one yellow - blue (which is also blue - yellow? No, wait, the color is just for distinction. Wait, the question is about the image for position 4. Let's think about the semi - conservative model. After two rounds of replication, the DNA molecules will be: two molecules with one original (blue) and one new (yellow) strand (from the first - round products) and two molecules with two new strands (yellow - yellow, which is Image I). Wait, position 4: let's track the replication.

First round (A): original (III: blue - blue) replicates to two DNA molecules, each with one blue and one yellow (II: blue - yellow). So 1 and 2 are II? Wait, maybe the left images: I is yellow - yellow, II is blue - yellow, III is blue - blue.

Second round (B): each of the two II (blue - yellow) DNA molecules will replicate. Each blue strand in II will make a new yellow strand, and each yellow strand in II will make a new blue strand. So from one II (blue - yellow), we get one II (blue - yellow, from blue template) and one I (yellow - yellow, from yellow template). So in the second round, the products (3 and 4) should be: one II (from the blue - yellow replicating to blue - yellow and yellow - yellow) and one I. Wait, position 4: if we follow the replication, after two rounds, the DNA molecules with two new strands (yellow - yellow) is Image I. So the roman numeral for position 4 is I.

Answer:

I