DrFantastic
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Hi,

Can someone explain the picture to me regarding Meselson Stahl?

I understand it's semi-conservative replication, but in f2 (generation 2), there are DNA strands which are not semi-conservative.

I'm really confused and don't understand how that can explain their results since it goes against the idea of semi-conservative replication?

Any help is greatly appreciated!
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Hype en Ecosse
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(Original post by DrFantastic)
Hi,

Can someone explain the picture to me regarding Meselson Stahl?

I understand it's semi-conservative replication, but in f2 (generation 2), there are DNA strands which are not semi-conservative.

I'm really confused and don't understand how that can explain their results since it goes against the idea of semi-conservative replication?

Any help is greatly appreciated!
That's still semi-conservative replication. Each helix of double-stranded DNA still consists of a parent strand, and the newly synthesised strand. Why do you think it's not?
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Joshalos
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(Original post by DrFantastic)
Hi,

Can someone explain the picture to me regarding Meselson Stahl?

I understand it's semi-conservative replication, but in f2 (generation 2), there are DNA strands which are not semi-conservative.

I'm really confused and don't understand how that can explain their results since it goes against the idea of semi-conservative replication?

Any help is greatly appreciated!
I'm assuming that the diagram is based of Stahl's experiment of growing bacteria in N-14 and N-15 solutions.

The parental generation is bacteria grown in Nitrogen-15 so the DNA contains only N-15 (blue).

F1, the next generation, bacteria is cultured in N-14 medium. Therefore, each DNA molecule consists of a N-14 and N-15 strand as each molecule retains a parent strand (from the N-15 medium) and synthesises a new strand (red) (using nitrogen in the N-14 medium).

F2 is still in a N-14 medium and so each strand retains a F1 strand and synthesises a new strand using nitrogen from the medium. As there are still N-15 strands in the F2 generation (semi-conservative) some molecules appear blue and red. The molecules that appear only red are still semi-conservative. They have retained a red N-14 strand from the previous generation and synthesised a new red N-14 strand from the medium. It is not that they are the same molecule, the colours purely denote the type of nitrogen used in the synthesis of the DNA.
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