Overview of Reductional & Equational Cell Division in Meiosis

Instructor: Adrianne Baron

Adrianne has a master's degree in cancer biology and has taught high school and college biology.

This lesson is going to give a general overview of the two divisions that take place during meiosis. We will take a look at why these divisions are referred to as reductional and equational division.


Having trouble remembering the difference between reductional and equational division? Let's go over it here.

All organisms that reproduce sexually rely on the process of meiosis. This is the cell division that is responsible for producing gametes that can be used for reproduction. Gametes are cells that are very different from the other cells in the body because they contain:

  1. unique combinations of the genetic material
  2. only half of the full number of chromosomes

Meiosis is an intricate process that ensures that no two gametes are identical, so that we don't give birth to clones. It also ensures that the amount of genetic material in each generation is the same as the previous generation. If we didn't create gametes, then our chromosome number would double with every new generation. Now let's discuss how the two divisions of meiosis create the gametes that we need for reproduction.

Reductional Division

The chromosomes within the cell are replicated before meiosis begins. There are two divisions that occur during the process of meiosis. The first division, called meiosis I, is often referred to as reductional division since it reduces the genetic material from diploid to haploid.

Let's get a quick refresher on what those two terms mean. Ploidy refers to the number of sets of chromosomes contained in the genome of a species. Diploid indicates that there are two sets of chromosomes and haploid means that there is one set of chromosomes. So again, reductional division ensures that we don't double our chromosomes every generation by halving the number of chromosomes in each gamete.

A tetrad is present at the beginning of meiosis I
Diagram of a tetrad

The replicated pairs of chromosomes, called homologous pairs, are joined together forming tetrads in the mother cell at the beginning phases of meiosis I. We refer to this as a tetrad since it contains 4 sister chromatids. During the process of meiosis I, the tetrads segregate so that two daughter cells each end up with one half of the tetrad. The half of a tetrad is essentially two paired sister chromatids. The two cells now have half of the number of chromosomes of the initial cell and are haploid.

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