Question

The events listed below are all necessary for homologous recombination to occur properly:

A. Holliday junction cut and ligated
B. strand invasion
C. DNA synthesis
D. DNA ligation
E. double-strand break
F. nucleases create uneven strands

Which of the following is the correct order of events during homologous recombination?
1) E, B, F, D, C, A
2) B, E, F, D, C, A
3) C, E, F, B, D, A
4) E, F, B, C, D, A

Answer 1

The correct order of events for homologous recombination is: double-strand break, nucleases create uneven strands, strand invasion, DNA synthesis, DNA ligation, and finally Holliday junction cut and ligated (sequence 4) E, F, B, C, D, A.

Step-by-step explanation:

The correct sequence of events during homologous recombination is as follows:

1. Double-strand break (E): This is the initiation step where the DNA double helix is broken.
2. Nucleases create uneven strands (F): Nucleases trim the ends of the broken DNA to produce 3' overhangs necessary for the next steps.
3. Strand invasion (B): One of the 3' overhangs invades the homologous DNA sequence and forms base pairs with its complementary strand, displacing the original complementary strand in the process.
4. DNA synthesis (C): DNA polymerase extends the invading 3' end using the homologous strand as a template.
5. DNA ligation (D): The extended strands and displaced strands are ligated to form a continuous DNA strand.
6. Holliday junction cut and ligated (A): The crossover structure known as the Holliday junction is resolved by cleavage and re-ligation to produce recombinant DNA molecule.

Therefore, option 4) E, F, B, C, D, A, is the correct order of events during homologous recombination.