The key difference between equational division and reduction division is that equational division refers to meiosis II, during which the chromosomal number remains equal as haploid. In contrast, reduction division refers to meiosis I, during which the chromosome number reduces to half from the diploid state.
Meiosis is a vital process in sexual reproduction. It facilitates the production of haploid gametes in order to keep the genetic material the same in each generation as the previous generation. It also ensures the production of genetically different gametes, which creates genetic variation. Meiosis occurs via two divisions as meiosis I and meiosis II. During meiosis I, the chromosome number is reduced from diploid to haploid. Hence, we call this division reduction division. During meiosis II, chromosome number remains as it is in the haploid state. Hence, we call this division an equational division.
CONTENTS
1. Overview and Key Difference
2. What is Equational Division
3. What is Reduction Division
4. Similarities Between Equational Division and Reduction Division
5. Side by Side Comparison – Equational Division vs Reduction Division in Tabular Form
6. Summary
What is Equational Division?
The equational division is the second division of meiosis. It is also known as meiosis II. Equational division begins from the two haploid cells produced by the reduction division. From two haploid cells, four haploid cells are produced in this phase. There is no change in the chromosome number of daughter cells. We call this phase equational division because it does not change the chromosome number of the cells.
Figure 01: Equational Division
Equational division resembles mitotic cell division. During equational division, individual chromosomes line up at the metaphase plate without pairing with the homologous chromosomes. During anaphase, centromeres split and sister chromatids separate from each other. Sister chromatids then migrate towards the opposite poles. Therefore, chromosome number remains constant (n) as the previous cell. At the end of the equational division, four haploid cells are produced.
What is Reduction Division?
Reduction division is the first division of meiosis. It is also known as meiosis I. As the name suggests, the chromosome number reduces in half. Therefore, the chromosome number decreases from diploid (2n) to haploid (n) state during the reduction division. There is a long interphase before meiosis I. Reduction division occurs via four subphases: prophase I, metaphase I, telophase I and anaphase I.
Figure 02: Reduction Division
During prophase I, homologous chromosomes recognize each other and form pairs. Then they form tetrads and exchange their genetic material between them. During prophase I, genetic recombination takes place. Genetic recombination increases the genetic variability within a species. During anaphase I, homologous chromosomes migrate towards the opposite poles. Since homologous chromosomes migrate into each pole, the chromosome number becomes half. Each daughter cell has only one copy of each chromosome. At the end of reduction division, two haploid daughter cells are produced. Reduction division is followed by equational division.
What are the Similarities Between Equational Division and Reduction Division?
- Equational division and reduction division are two divisions of meiosis.
- Both divisions produce haploid cells.
- Reduction division is followed by equational division.
- Both divisions have four subphases.
- There is no interphase between these two divisions.
- They happen in the sexual reproduction process, during the sex cell formation in spermatogenesis and oogenesis.
- Daughter cells resulting in each division are genetically different.
What is the Difference Between Equational Division and Reduction Division?
In equational division, genetic material is transmitted equally into daughter cells. In reduction division, genetic material is reduced in half and transmits to daughter cells. So, this is the key difference between equational and reduction division. Furthermore, four daughter cells are produced at the end of an equational division, while two daughter cells are produced at the end of the reduction division.
Moreover, homologous chromosome pairing and genetic recombination occur during the reduction division while they do not happen in the equational division. Thus, this is another difference between equational and reduction division.
The below infographic lists all the important differences between equational and reduction division in tabular form.
Summary – Equational Division vs Reduction Division
Two divisions of the genetic material take place during meiosis. These divisions are called reduction division (meiosis I) and equational division (meiosis II). In the reduction division, the chromosome number is reduced to half. In the equational division, chromosome number remains in the haploid state without reducing. Genetic material is transmitted equally into four daughter cells. Thus, this is the key difference between equational and reduction division.
Reference:
1. “Overview of Reductional & Equational Cell Division in Meiosis.” Study.com, Available here.
2. “Replication and Distribution of DNA during Meiosis.” Nature News, Nature Publishing Group, Available here.
Image Courtesy:
1. “Meiosis2” By Boumphreyfr – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Meiosis1” By Boumphreyfr – Own work (CC BY-SA 3.0) via Commons Wikimedia