Anaphase I vs Anaphase II
The basic unit of structure of an organism is cell. A new cell begins with the pre-existing cell, which is an essential process for continuity of life. Nuclear division and cell division are two steps in cell division.
Mitosis and meiosis are two forms of nuclear division that occur in a cell. As a result of mitosis, nucleus divides into two daughter cells, and each has the same chromosomal number as the parent nuclei has. However, in meiosis, number of nuclear chromosomes that daughter cells have, is halved from the parent nuclei. Meiosis occurs when sperm and eggs are formed in animals and spore formation in plants (Taylor et al, 1998). As a result of meiosis, four daughter cells are formed from one parent cell, may be with a genetic variation.
Meiosis includes two successive nuclear divisions; i.e. meiosis I and meiosis II, which result in four haploid cells from a diploid cell. Both these meiosis I and meiosis II have four phases i.e. prophase, metaphase, anaphase, and telophase. Anaphase I occurs at meiosis I, whereas anaphase II occurs at meiosis II.
This is the subsequent step of metaphase I where the two homologous chromosomes are arranged in the equator of the spindle. These chromosomes are attached to the spindle by their centromeres (Taylor et al, 1998).
At the beginning of Anaphase I, cell starts to lengthen. As a result of lengthening of the cell, spindle fiber stretch towards opposite poles, separating the homologous chromosomes into haploid sets (Taylor et al, 1998).
Anaphase II occurs at meiosis II, which is similar to anaphase of mitosis. Anaphase II follows the metaphase II. At the end of metaphase II, haploid chromosomes are arranged around the equator of the spindle. When the spindle fibers stretch out to the opposite poles, chromatids are separated splitting from their centromeres.
What is the difference between Anaphase I and Anaphase II?
• The main difference between anaphase I and anaphase II is that anaphase I occurs in a diploid cell and anaphase II occurs in a haploid cell.
• In anaphase I, centromeres of homologous chromosomes are attached to the spindle fibers so as the two spindle fibers are attached to the centromeres of each homologous chromosome whereas, in anaphase II, both spindle fibers are attached to the same chromosome.
• In the anaphase I, homologous chromosomes (bivalent) separate to opposite poles, retaining sister chromatids together, whereas anaphase II chromatids of a chromosome separate to opposite poles, splitting the centromere.
• In anaphase I, splitting of centromere do not occur whereas, in anaphase II, sister chromatids separate, splitting the centromere.
• At the end of anaphase I, one homologous chromosome will go to each daughter cell whereas, at the end of anaphase II, one sister chromatid will exist in each daughter cell.
• Anaphase II is similar to the mitosis anaphase whereas, anaphase I is not similar to the mitosis anaphase.
• In anaphase I, chromosomes are arranged around the equator of the spindle whereas, in anaphase II, plate of the chromatids arrangement is rotated by 90° relative to the arrangement in anaphase I.
Taylor, D.J., Green N.P.O., Stout, G.W., (1998), Biological Science. Cambridge University Press, Cambridge