Name the stage of prophase I that fits each clue…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Name the stage of prophase I that fits each clue.
- The chromosomes become gradually visible as thin threads.
- The homologous chromosomes start to pair, and a synaptonemal complex forms.
- Recombination nodules appear, and crossing over takes place.
- The synaptonemal complex dissolves, and X-shaped chiasmata are seen.
- The chiasmata move to the ends. The nucleolus and the nuclear envelope disappear.
Need a reminder? The key ideaShow
Meiosis copies the DNA once and divides twice. Homologous chromosomes pair in zygotene, cross over in pachytene, show chiasmata in diplotene, and the chiasmata move to the ends in diakinesis. A bivalent is a pair of homologues and holds four chromatids.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Leptotene.
Step 2. (b) Zygotene. The pairing is synapsis.
Step 3. (c) Pachytene. The four chromatids of each bivalent are clear.
Step 4. (d) Diplotene.
Step 5. (e) Diakinesis. The chiasmata move to the ends, which is terminalisation. The cell is ready for metaphase I.
Answer: (a) leptotene; (b) zygotene; (c) pachytene; (d) diplotene; (e) diakinesis.
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