TBR Biology VI Passage XIII #85 Nondisjunction

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meilideai

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I am having trouble understanding the picture in the solutions.

Question states primary nondisjunction occurs during Meiosis I, secondary nondisjunction occurs during Meiosis II. Question asks for secondary nondisjunction diagram in spermatogenesis.

I drew a diagram, starting with 2n (2 chromosome pairs of different types - colored them white and gray). I went through Meiosis I and got 2 daughter cells that are haploid, one with the white chromosome, the other gray chromosome. Then I'm ready to draw the nondisjunction that occurs, and assumed nondisjunction in both daughter cells, coming out with 4 cells of the following:

1- 2 white sister chromatids
2- empty cell
3- 2 gray sister chromatids
4- empty cell

did I do something wrong here or am I not understanding Meiosis?

Answer was
1- Empty cell
2- 2 chromatids
3- 1 chromatid
4- 1 chromatid

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... Then I'm ready to draw the nondisjunction that occurs, and assumed nondisjunction in both daughter cells, coming out with 4 cells of the following...

You did double secondary nondisjunction which is valid but with very little probability.
 
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