Question

How many chromstid are attached with one chromosime in anaphase 2?

Answer 1

This is quite a common confusion that many people face when trying to understand mitosis and meiosis. I admit it took me a really long time as well to get all the basics sorted out.  

So I'll try to explain this as clearly as possible.

The first thing to know is the difference between a chromatid and a chromosome.

Next, let's look at the basics of chromosome numbers in mitosis.

So it's more or less straightforward in mitosis:

The chromosome number remains constant (46 total chromosomes or 23 pairs of chromosomes).

The chromatids replicate during interphase to produce a total of 92 chromatids, but they're only found in pairs and remain connected at the center by the centromere.

After mitosis, the chromatid pairs separate, so each daughter cell gets 46 chromatids.

Now meiosis is tricky. Meiotic cells undergo a more complicated process to ensure the correct number of chromosomes.

Here's what happens:

At first the cells have the same number of chromosomes as mitosis. DNA replication occurs, giving a total of 46 chromosomes (or 23 chromosome pairs) and 92 chromatids (or 46 chromatid pairs).

Meiosis I: In meiosis I, the homologous chromosomes separate. In this case, the pairs of sister chromatids are still attached to each other. So at this stage, the daughter cells get 23 chromosomes each (of the pair of homologous chromosomes) and 46 chromatids in total (which are actually 23 pairs of sister chromatids attached at the centromere). This is known as reductional division, as the total number of chromosomes is halved at this stage.

Meiosis II: Meiosis II follows the same division as mitosis, except that there are only half as many chromosomes. So the 23 chromatid pairs from the previous cells (or 46 chromatids in total) split equally, so each daughter gets 23 chromatids exactly, which correspond to 23 chromosomes. Meiosis II is known as equational division.

So to summarize, in mitosis, the total number of chromosomes is unchanged in the daughter cells; whereas in meiosis, the total number of chromosomes is halved in the daughter cells.

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