Question

What two events DO NOT take place in the Synthesis-Dependent Strand-Annealing (SDSA) model of recombination?

a. D-loop strand displacement and DNA synthesis
b. Strand annealing and ligation
c. DSB resection and strand invasion
d. 5'-second-end capture and Holiday structure formation (hence no crossing over)

5'-second-end capture and Holiday structure formation (hence no crossing over)

Answer 1

In SDSA recombination, 5'-second-end capture and Holiday structure formation do not occur. Instead, it involves strand annealing and ligation to repair chromosomal DNA without crossing over.

Step-by-step explanation:

The two events that do not take place in the Synthesis-Dependent Strand-Annealing (SDSA) model of recombination are 5'-second-end capture and Holiday structure formation, which would lead to crossing over. In contrast, strand annealing and ligation do occur in this process. SDSA aims to repair a double-stranded break in chromosomal DNA without the reciprocal exchange of genetic material that characterizes traditional crossing-over events. During SDSA, helicase unwinds the DNA and allows for the repair process, but the DNA ends are not captured again (no second-end capture) after they are extended, and thereby, the Holliday junctions typical in other recombination processes, like Double Holliday Junction (DHJ), are not formed.