Final answer:
In the single-strand annealing model of homologous recombination, Holliday junctions are not formed. Complementary single-stranded DNA segments anneal directly to each other after processing, without a crossover of genetic material.
Step-by-step explanation:
In the single-strand annealing model, Holliday junctions are not formed. Single-strand annealing is a specific type of homologous recombination that occurs without the formation of Holliday junctions, intermediates that typically appear in other recombination processes. Instead, this process involves the annealing of complementary single-strand DNA sequences following DNA damage. The ends of the DNA are processed to reveal single-stranded regions, which can then base pair with each other. While homologous pairing and DNA synthesis do occur as the single-strand ends are trimmed and repaired, the distinct multibranched structures called Holliday junctions, which facilitate crossover of genetic material, are absent in this pathway.