Mei studies a pea plant, which has 2n = 14 chromosomes in its body cells…
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Mei studies a pea plant, which has chromosomes in its body cells. A pollen mother cell enters prophase I.
- How many bivalents form?
- How many chromatids are in all the bivalents together?
- How many centromeres are there in the cell?
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
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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.
Given. .
Plan. Pair the chromosomes. Then count the chromatids and the centromeres.
Step 1. Bivalents. .
Step 2. Chromatids. Each of the chromosomes has two chromatids. . Check: bivalents chromatids .
Step 3. Centromeres. There is one centromere in each chromosome, so . The two sister chromatids share a centromere.
Answer: bivalents; chromatids; centromeres.
Check. Every bivalent holds two centromeres and four chromatids.
Watch out. The cell does not have bivalents. It has chromosomes in bivalents.
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