Self Assessment Answer # 3
for Lesson 4

by Dr Jamie Love © 2002 - 2010
Genetics Course

This diagram may help you through the first three questions (about mitosis).

A

  1. After mitosis each nuclei will have 22 chromosomes so the nuclei are diploid. Recall that anaphase of mitosis creates chromosomes from chromatids.
  2. After mitosis, but before cytokinesis, each cell will have 44 chromosomes, 22 in each nucleus, so the cell is polyploid. Remember, the cell doesn't divide until cytokinesis, so it still has two diploid nuclei. That makes it 4n so it's polyploid! Tetraploid to be exact.
  3. After cytokinesis, following mitosis, each cell has 22 chromosomes so the cells are diploid. Now things are as they should be.

This diagram may help you through the remaining questions.

Also, it may help to understand that an organism with 22 chromosomes as its diploid number has a haploid number of 11. (Right?)

B

  1. After meiosis I each nuclei will have 11 chromosomes so the nuclei are haploid. Anaphase I separates the tetrads into dyads. No chromosomes are "split" so chromatids remain as chromatids. Meiosis I, specifically anaphase I, is the "true" reduction division.
  2. After meiosis I, but before cytokinesis, the cell will have 22 chromosomes, 11 in each nuclei, so the cell is diploid.
  3. After cytokinesis, following meiosis I, each cell will have 11 chromosomes because each cell now has one haploid nucleus - so the cell is haploid.
C
  1. After meiosis II each nuclei will have 11 chromosomes so the nuclei are haploid. Anaphase II of meiosis creates chromosomes from chromatids.
  2. After meiosis II, but before cytokinesis, the cell will have 22 chromosomes in two haploid nuclei - so the cell is diploid!
  3. After cytokinesis, following meiosis II, each cell will have 11 chromosomes because each cell now has one nucleus containing 11 chromosomes - so each cell is haploid.

[Phew! ]

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