Meiosis

Basics of Meiosis

  • Meiosis is a type of cell division that reduces the number of chromosomes in parent cells by half to produce four daughter cells, each with half the chromosomes of the parent.
  • This process is critical for sexual reproduction as it ensures the offspring have the correct number of chromosomes.

Stages of Meiosis

  • Meiosis consists of two successive nuclear divisions with no replication of DNA in between, which are known as Meiosis I and Meiosis II.
  • Each of these stages can be further divided into prophase, metaphase, anaphase, telophase and cytokinesis.

Meiosis I

  • Prophase I: Chromosomes condense and pair up in homologous pairs, crossing over occurs causing an exchange of genetic material.
  • Metaphase I: The paired chromosomes line up at the equator, independently assort to increase genetic variation.
  • Anaphase I: The homologous pairs are pulled apart to opposite poles of the cell.
  • Telophase I and Cytokinesis: Chromosome sets gather at the poles of the cell and two daughter cells are formed, each with a haploid set of chromosomes.

Meiosis II

  • Prophase II: The chromosomes re-condense.
  • Metaphase II: The chromosomes line up at the equator of the cell.
  • Anaphase II: The sister chromatids are pulled apart to opposite poles of the cell.
  • Telophase II and Cytokinesis: The chromatids gather at the poles of the cell. Four haploid daughter cells are formed, each genetically different due to crossing over and independent assortment.

Contribution of Meiosis to Genetic Diversity

  • Meiosis contributes to genetic diversity in two main ways: crossing over and independent assortment.
  • Crossing over involves the exchange of DNA between homologous chromosomes during prophase I. This results in new combinations of genes on each chromosome.
  • Independent assortment occurs during metaphase I, when pairs of homologous chromosomes line up at the equator, resulting in an exchange of genetic material among non-sister chromatids.
  • Together, these processes create a vast number of genetically unique gametes, increasing genetic diversity in populations and contributing to evolution.

Comparison of Meiosis and Mitosis

  • Meiosis creates four non-identical, haploid cells that are used for sexual reproduction, while mitosis creates two identical, diploid cells for growth and repair.
  • Mitosis only goes through one cycle of division, but meiosis goes through two.
  • During metaphase of mitosis, individual chromosomes line up at the equator, whereas in metaphase I of meiosis, pairs of homologous chromosomes do.