Question

For the following two cells, determine the specific stage of mitosis or meiosis depicted (explain your reasoning for each).

The following cell is from an organisms where 2N=8.

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b) The following cell is from an organism where 2N=12

Answer 1

For both the pictures of dividing cells, the cells are in anaphase stage. But you have to understand that what kind of cell division is happening here, is it mitosis or meiosis?

Firstly, for both the dividing cells the chromosomes are moving from the center of the cell to the opposite poles. This is the typical characteristics of anaphase, and this movement of chromosomes is called poleward movement.

Now, for the first figure, the cell chromosome number, 2N = 8 and you can see from the picture that 4 pairs of chromosomes are moving towards each pole. It is the characteristic of both the mitosis and meiosis. But if you look carefully, you can see that the sister chromatids are not separated. This is exclusively seen in the Anaphase I of Meiosis I. So, the cell division stage is Anaphase I of Meiosis I. (For anaphase of mitosis, sister chromatids will move in opposite direction detaching from each other)

b) Now, for the 2 nd figure,

2N = 12 and the sister chromatids are also separated. So, it could be mitosis or Anaphase II of Meiosis II. But if you count the number of chromatids moving in each direction, it is 6 (or 'n'). So, the cell division stage is Anaphase II of Meiosis II. For mitosis the number of chromosomes moving in each direction would have been 12 (or, 2n)