When and how do homologous chromosomes separate during meiosis?

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Homologous chromosomes separate during the first division of meiosis, which is called meiosis I. More specifically, this separation happens in the anaphase I stage of meiosis I.

Before this stage, in the earlier phase of meiosis I called prophase I, homologous chromosomes come close to each other and form pairs. This process is called synapsis. Each pair has two chromosomes (one from the mother and one from the father) that carry similar types of genes. These pairs are called bivalents or tetrads, because they have four chromatids.

Then, in metaphase I, these homologous chromosome pairs align themselves at the centre of the cell (equator). They are attached to spindle fibres from opposite poles of the cell.

Now comes the most important step i.e., anaphase I. In this stage, the spindle fibres pull the homologous chromosomes apart. One chromosome from each pair is pulled to one side of the cell and the other chromosome goes to the opposite side. This is the point where homologous chromosomes separate. It is important to note that the sister chromatids of each chromosome do not separate at this stage. They remain attached to each other at the centromere.

As a result, each new cell formed after meiosis I gets only one chromosome from each homologous pair. This reduces the chromosome number by half, which is why meiosis I is called a reductional division.

The separated chromosomes then reach the poles during telophase I and two haploid cells are formed after cytokinesis.

In short:

When homologous chromosomes separate during meiosis?

The answer is during anaphase I of meiosis I

How do homologous chromosomes separate during meiosis?

The answer is by pulling of spindle fibres that move one chromosome from each homologous pair to opposite poles

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