Tutorial: Chromosomes in meiosis

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Meiosis comprises two successive divisions. During meiosis I the number of chromosomes is halved and recombination takes place. Recombination ensures that the gametes that are produced are genetically different. Meiosis II is essentially a mitotic division that is not preceded by replication of DNA.

 

For scholars:

Draw the progression of two pairs of chromosomes through meiosis I

• One chromosomes pair is metacentric and the other acrocentric.
• Follow the clues and complete the templates for metaphase I, anaphase I and telophase I.
• Do not take crossing over into account in this tutorial.
• Tip: Recall that the centromeres of the bivalents attach to the spindle, therefore when the chromosomes move towards the poles the centromeres will be closest to the poles.
• Tip: Make sure that you take into account the lengths of the arms of the chromosomes.

Draw the progression of two pairs chromosomes through meiosis II

 

Questions:

Choose the appropriate words:
1. The chromosomes in one gamete are in one gamete are homologous / non homologous.
2. A chromosome at an anaphase I pole has 1 / 2 chromatin strands.
3. A chromosome at an anaphase II pole has 1 / 2 chromatin strands.

4. Give a symbolic representation of the gametic chromosome number.