Link Search Menu Expand Document
Senanu's Bio class

Meiosis and the sexual life cycle

The reading guide is here.

  • After completing your reading, test your knowledge of mitosi and meiosis by filling in this worksheet.

  • Here’s a fun introduction to sexual reproduction and meiosis. One point of clarification: in this crash course video, he says that the X and Y chromosome are not homologous and want nothing to do with each other during prophase of meiosis. This is not correct. X and Y are not considered homologous because they don’t contain the same genes, but they do line up with each other during prophase. Each has regions called the “pseudo-autosomal region” (PAR1 and PAR2 in humans) that does have the same DNA and the cell uses that to line the X up with the Y. In fact, there is also crossing over at these regions and the few genes within these regions are inherited like autosomal genes rather than sex-linked genes, despite being on the sex chromosomes. You can find out a lot more about it in this paper which should be freely available.

  • Meiosis video.

Modeling meiosis

This exercise is similar to the one for mitosis. If you haven’t done that one yet, please do it first.

You will need:

  • 4 forks. 2 of them should be plastic, 2 of them should be metal.
  • 4 spoons, 2 of them plastic and 2 metal.

What to do

  1. As you did with the mitosis model, start your cell at G1 phase. You should have 1 metal and 1 plastic fork, and 1 metal and 1 plastic spoon. These represent homologous chromosomes, because they are similar but not identical.
  2. S-phase. Duplicate each chromosome by adding another identical utensil alongside the original. The two identical utensils represent sister chromatids.
  3. Enter meiosis. Position your pairs of sister chromatids alongside the other homologous pair of sister chromatids. In other words, all 4 forks should be together in a tetrad. Your 4 spoons should also be in a tetrad. This is when crossing over takes place.
  4. Line up your tetrads on the metaphase plate.
  5. In anaphase, your homologous chromosomes will be separated. Sister chromatids should stay together until meiosis II.
  6. Telophase and cytokinesis complete the first cell division.
  7. Start meiosis II. The sister chromatids are still attached, and they line up on the metaphase plate. There is no pairing of homologous chromosomes like there was in meiosis I.
  8. During anaphase II, the sister chromatids are separated by the spindle microtubules.
  9. Telophase and cytokinesis complete the division of the cell.
  10. Make sure that your 4 cells each have 1 fork and 1 spoon. If they don’t, you did something wrong.
  11. Run through it again – it’ll only take a minute this time.