Final answer:
In the synaptonemal complex, strand exchange between chromosomes occurs at an average distance of 100-200 nm. This process, known as crossing over, is crucial for the formation of chiasmata and the resulting genetic recombination during meiosis I.
Step-by-step explanation:
In the synaptonemal complex, strand exchange between chromosomes occurs at an average distance of 100-200 nanometers (nm). This exchange happens through a process known as crossing over or crossover, where chromosomal segments are exchanged between non-sister homologous chromatids. This exchange can be observed as chiasmata, which are visually identifiable under a microscope. The proper separation of homologous chromosomes during meiosis I requires at least one chiasma per chromosome, ensuring genetic diversity through recombination.
During prophase I of meiosis, the synaptonemal complex forms and supports the tight pairing of homologous chromosomes in a process called synapsis. Recombination nodules located along the synaptonemal complex mark the points of crossover and play a critical role in genetic recombination. The synaptonemal complex eventually breaks down and the chromosomes, which remain attached at the chiasmata, are called tetrads comprising four sister chromatids. The cohesin connection between homologous pairs is removed except at the chiasmata, allowing for proper separation during meiosis.
Therefore, option B (100-200 nm) is the correct answer, as it represents the average distance where strand exchange in the synaptonemal complex occurs.