Final answer:
The X-shaped intersections observed during crossing over are called chiasmata, which are essential for genetic recombination in meiosis. The question's correct answer is b. Chiasmata.
Step-by-step explanation:
The X-shaped structures that pinpoint the positions where exchange occurs during crossing over between homologous chromosomes are called chiasmata.
During prophase I of meiosis, the synaptonemal complex forms, facilitating the tight pairing of homologous chromosomes in a process called synapsis.
This complex supports the exchange of chromosomal segments between non-sister homologous chromatids, enabling genetic variation. The points where these exchanges occur and are visually observed are known as chiasmata. As meiosis continues, the synaptonemal complex breaks down, but the homologous chromosomes remain connected at the chiasmata until they are separated into different cells. The correct answer to the question is b. Chiasmata.