IMAT 2018 Q26 [Eukaryotic Cell Division]

A eukaryotic cell undergoes division. At one point it has pairs of chromosomes being separated by spindle fibres and moving towards the poles of the cell.

What stage of division is this?

A. anaphase in Meiosis I
B. anaphase in Mitosis
C. metaphase in Mitosis
D. metaphase in Meiosis II
E. telophase in Meiosis I

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Knowing the mitosis and meiosis stages must be known the steps like the back of your hand. The first thing we can do is identify when the action occurs because the pulling of chromosomes to opposite poles is something that occurs in anaphase no matter whether mitosis or meiosis (and yes, there are differences). Let’s recall what happens in anaphase: after metaphase, where the chromosomes (or homologous pairs - in meiosis 1) are aligned in the centre with the spindles attached, then in anaphase, the spindles from the centrosomes attach to the centromeres of the chromosomes. When we are pulling the chromosomes apart, we have a double here in the number of chromosomes but not chromatid. That sounds confusing, right? Here is a trick, we can identify the number of chromosomes during mitosis by the number of centromeres. In anaphase 1 of meiosis, there is no doubling of chromosomes, and this is because tetrads and pulled apart to give each daughter cell a chromosome consisting of 2 chromatids.

Back to the question, we can eliminate C, D, and E as they do not involve anaphase. Now we are left to choose between anaphase in mitosis and in meiosis 1. As previously stated, meiosis 1 involves the separation of homologous chromosomes that were a part of a tetrad in anaphase 1. These chromosomes are in their homologous pairs, so we can say that the pair of chromosomes are being separated by the spindle fibres and moving to opposite poles, which is what is being asked in the question.

\fcolorbox{red}{grey!30}{Therefore A, Anaphase 1 in meiosis, is correct.}