The X-shaped structures formed at the sites of crossing over between homologous chromosomes become clearly visible during which stage of Prophase I?
Answer and explanation
Correct answer: B. Diplotene
- Step 1: During Pachytene, crossing over takes place, but the tight synaptonemal complex holds homologous chromatids together along their entire length.
- Step 2: As cells transition into Diplotene, the synaptonemal complex dissolves, and the homologous chromosomes separate from each other.
- Step 3: The chromosomes remain attached only at the points of previous crossing over, forming visible X-shaped configurations called chiasmata.
Answer
Diplotene.
Why not the others: Pachytene is when crossing over occurs, but chiasmata are not yet visible due to the intact synaptonemal complex; Zygotene is when synapsis initiates; Diakinesis is characterized by terminalization of chiasmata.
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