In a girl's ovary before she is born, the primary oocytes begin meiosis and stop in diplotene…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In a girl's ovary before she is born, the primary oocytes begin meiosis and stop in diplotene. NCERT says that diplotene can last for months or years in the oocytes of some vertebrates.
- What structures hold the homologues together in diplotene?
- Suppose that one oocyte stays in diplotene from the birth of the woman until it is released at the age of years. About how many years is that?
- Is the cell haploid or diploid in diplotene? How many chromatids does a bivalent have?
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) The chiasmata. The homologues tend to separate, except at the points of crossing over.
Step 2. (b) About years, if the oocyte started at birth. This is a simple count of the age.
Step 3. (c) The cell is still diploid, because meiosis I has not separated the homologues. Each bivalent has four chromatids.
Answer: (a) chiasmata; (b) about years; (c) diploid, four chromatids.
Source. NCERT, Class XI Biology, chapter 10 (diplotene can last for months or years in some oocytes).
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