A species has 12 pg of DNA in a diploid cell in G1 phase…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A species has pg of DNA in a diploid cell in G1 phase. This is an invented value, used to practise the method.
- How much DNA does the cell have after S phase?
- How much DNA does each cell have after meiosis I?
- How much DNA does each gamete have after meiosis II?
- How much DNA does the zygote have just after fertilisation, before S phase?
Need a reminder? The key ideaShow
Meiosis I separates the homologues, and each cell gets half the chromosomes, each of two chromatids. Meiosis II separates the sister chromatids. The DNA of a human cell goes C, C, C and C. A cell in anaphase II has the diploid number of chromosomes, but only C of DNA.
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.
Given. pg in G1.
Plan. Double once, halve twice, then add two gametes.
Step 1. After S phase. pg.
Step 2. After meiosis I. The pg is shared by two cells. pg in each.
Step 3. After meiosis II. Each of the two cells divides again. pg in each gamete.
Step 4. The zygote. Two gametes join: pg. This is the amount of a diploid G1 cell.
Answer: pg; pg; pg; pg.
Check. In units of C: C, C, C, C and back to C.
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