Dictionary > Metaphase I

Metaphase I

Definition
noun
The second stage in the first meiotic division after prophase I, and highlights the alignment of paired homologous chromosomes along a single plane in the center of the cell
Supplement
Meiosis is a specialized form of cell division that ultimately gives rise to non-identical sex cells. There are two successive nuclear divisions: meiosis I and meiosis II. Each of them has four major phases. These are prophase, metaphase, anaphase and telophase. Each of these phases is designated as I or II depending where it occurs, i.e. in meiosis I or in meiosis II.
Metaphase I is the second stage in meiosis I. It follows prophase I, which highlights the pairing of and the exchange of DNA between homologous chromosomes through homologous recombination and crossover at chiasma(ta) between non-sister chromatids.
At metaphase I, the homologous chromosomes move to the center of the cell and orient themselves along an equatorial plane, forming the so-called metaphase plate. It should be noted that because of the previous homologous recombination and crossovers, the four chromatids that make up each pair of homologous chromosomes are genetically dissimilar at this point. The spindle fibers attach to the kinetochores of the centromere, preparing the chromosomal pair to be separated during the next phase, anaphase I.
The main differences between meiotic metaphase I and mitotic metaphase are as follows:

  • In mitosis, the chromosomes (each with two chromatids) line up on the metaphase plate whereas in meiosis, the tetrads (where each chromosomal pair has four chromatids joined at the centromere) line up on the metaphase plate.
  • In mitosis, the centromeres (i.e. the region containing the kinetochores) lie on the equatorial plane whereas in meiosis, the centromeres are directed towards the poles while the chromatids lie on the equatorial plane.

See also:

  • meiosis I
  • metaphase
  • chiasma
  • homologous chromosome
  • centromere


    You will also like...

    DNA carries genes coding for proteins
    Genetic Information and Protein Synthesis

    Genes are expressed through the process of protein synthesis. This elaborate tutorial provides an in-depth review of the..

    Growth Patterns
    Growth Patterns

    This tutorial describes the sigmoid curve, annual plant growth, tree growth, human growth, and insect growth as the grow..

    Balanced Diet
    A Balanced Diet – Minerals and Proteins

    Proteins and minerals can be derived from various dietary sources. They are essential for the proper growth and developm..

    Body temperature regulation by the hypothalamus
    Temperature Regulation in Animals

    This tutorial elucidates body temperature regulation. Know the details here to learn how the body sets the body temperat..

    Ecosystem Succession
    Ecosystem Succession

    If the balance of nature is left untouched, landscapes can change dramatically over time. A previous ecosystem is supers..

    Direct and indirect physiologic effects of growth hormone
    Animal Growth Hormones

    Hormones are produced in the endocrine glands of animals. The pituitary gland and hypothalamus are the most impor..