MEIOTIC DIVISION

1. MEIOSIS
THE DIFFERENCE BETWEEN MEIOSIS 1 AND 2
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2. The meiotic division is divided into meiosis 1 and meiosis 2. Gametes required for the sexual
reproduction of organisms are produced through meiosis. Meiosis 1 is the initial period of the cell
cycle and is followed by meiosis 2. During meiosis 1, homologous chromosomes are separated
into two daughter cells, reducing the chromosome number by half, relative to the parent
cells’ chromosome number (King et al., 1998). The second division of meiosis is meiosis 2 which
is involved in the equal segregation and separation of bivalent chromosomes. Meiosis 2 is only
physically similar to the mitosis, not genetically since it produces haploid cells, which are used as
gametes later, starting from diploid cells. Both stages of meiosis 1 and 2 consist of four phases:
prophase, metaphase, anaphase, and telophase. Homologous tetrads are divided into two daughter
cells at the meiosis 1. The resulting bivalent chromosomes in one daughter cell are divided into
two daughter cells, containing single sister chromatids in each (King et al., 1998). Four daughter
cells are formed, containing a single sister chromatid of each chromosome from the parent cell.
The main difference between meiosis 1 and meiosis 2 is that during meiosis 1, chromosomal
cross-over occurs at the prophase 1, leading to the genetic recombination whereas no chromosomal
cross-over is identified during meiosis 2
Meiosis 1 is composed of four phases: prophase 1, metaphase 1, anaphase 1 and telophase 1.
During prophase 1, homologous chromosomes are paired by an event known as synapsis. During
synapsis, genetic variation is allowed by two ways (Armstrong et al., 2001). First is the
independent orientation of the pairs of the homologous chromosomes in the cell equator. This is
called the law of independent assortment, allowing the segregation of maternal and paternal
chromosomes in a random nature. Secondly, the chromosomal cross-over at chiasmata of non-
sister chromatids during prophase 1 allows the genetic recombination of chromosomes to occur,
resulting in new combinations of alleles in the inherited chromosomes (Armstrong et al., 2001).
A series of prophase sub phases can be identified depending on the appearance of the
chromosomes. They are leptotene, zygotene, pachytene, diplotene, diakinesis and synchronous
processes. Throughout these stages, the disappearance of the nucleolus, the formation of meiotic
spindle between the two centrosomes in the opposite poles of the cytoplasm, the disappearance of
the nuclear envelope, and the invasion of the nucleus by the spindle microtubules take place
sequentially. Prophase 1 consumes 90% of the time taken to complete the whole meiosis (Sybenga,
1999)
During metaphase 1, homologous chromosome pairs are arranged in the cell equator. A
single kinetochore microtubule from each pole is connected with one centromere of the
homologous chromosome pair (Sybenga, 1999). By the contractions of the kinetochore
microtubules due to the generating tension, cohesion proteins at the chromosomal arms are
cleaved, separating the homologous chromosomes from each other at the anaphase 1. The
separated chromosomes are pulled to the opposite poles by the kinetochore microtubule
contraction at the telophase 1 (Armstrong et al., 2001).

3. After the completion of telophase 1, new nuclear envelopes are formed surrounding the
chromosomes in the opposite poles. Telophase 1 is followed by interkinesis, which is a resting
phase by separating the two daughter cell’s cytoplasm
Meiosis 2 proceeds through four sequential phases: prophase 2, metaphase 2, anaphase 2 and
telophase 2. During prophase 2, nuclear envelope and nucleolus disappear, thickening the
chromatids to form chromosomes. A new pair of centrosomes appears in the opposite poles of the
second cell equator, which is in a rotated position by 90 degrees relative to the meiosis 1 cell
equator (Armstrong et al., 2001). The second spindle apparatus is formed from the two, new
centrosomes. During metaphase 2, centromeres of the individual chromosomes are attached
to the two kinetochore microtubules from either side. The chromosomes are aligned on the second
cell equator (King et al., 1998).
During anaphase 2, centromeric cohesins are cleaved, segregating the two sister chromatids.
During telophase 2, separated sister chromatids, which are known as the sister chromosomes, are
moved towards the opposite poles by the contractions of the kinetochore microtubules.
Decondensation of chromosomes, as well as the disassembling of the spindle apparatus, mark the
end of the telophase 2 (King et al., 1998). The nuclear envelopes and nucleoli are formed,
following the division of the cytoplasm, which is known as the
The difference between meiosis 1 and 2 in terms of chromosomes presence, number of daughter
cell produced, crossing over, complexity, time taken, cleavage of the cohesin complex and phases.
Meiosis 1 is a heterotypic division, reducing the chromosome number in the daughter cell by half,
compared to the parent cell while Meiosis 2 is a homotypic division, equalizing the chromosome
number of both parent and daughter cells. Homologous chromosomes are present at the beginning
of meiosis 1 but individual, bivalent chromosomes are present at the beginning of meiosis 2.
Prophase 1, metaphase 1, anaphase 1 and telophase 1 are the four phases in the meiosis 1 while
meiosis is made up of Prophase 2, metaphase 2, anaphase 2 and telophase 2. For meiosis 1
individual chromosomes are present in the daughter nuclei while in meiosis 2 sister chromosomes,
which are derived from sister chromatids are present in the daughter nuclei. Number of Daughter
Cells at the End Meiosis 1 while and the two daughter cells produced at meiosis 1 are separately
divided to produce four cells in meiosis 2. Cross-over in Meiosis 1 occurs during prophase 1, by
exchanging the genetic material between non-sister chromatids while in Meiosis 2 there is no
chromosomal cross-over occurring. Time taken in Meiosis 1 is a more since it is a complex
division. Thus, it takes more time while Meiosis 2 is comparatively simple and less time is taken
for the division. Interphase is followed by meiosis. No interphase takes place prior to the meiosis
thus a resting phase, interkinesis can occur. Meiosis 1 Cohesin protein complexes at the arms of
the homologous chromosomes are cleaved. Meiosis 2 Cohesins at the centromeres are cleaved in
order to separate the two sister chromatids
In conclusion Meiosis is the mechanism of producing gametes during the organisms’ sexual
reproduction. Meiosis occurs through two stages, meiosis 1 and meiosis 2. Each stage is composed
of four phases, prophase, metaphase, anaphase and the telophase. During meiosis 1, homologous

4. chromosomes pair follow the law of independent assortment. Chromosomal cross-over takes place
between non-sister chromatids at chiasmata, leading to produce new combinations of alleles
through genetic recombination. Homologous chromosomes of a diploid parent cell are separated
into two haploid daughter cells at meiosis 1. Meiosis 2 is similar to the mitotic cell division,
equalizing the number of chromosomes in a parent cell produced at meiosis 1 and daughter cell,
produced by meiosis 2. The main difference between meiosis 1 and meiosis 2 is that genetic
recombination occurs in meiosis 1 and no recombination of DNA can be observed in meiosis 2.
REFERENCES
Armstrong SJ, Caryl AP, Jones GH, Franklin FCH.2002. Asy1 protein, required from chromosome
synapsis, localizes to axis‐associated chromatin in Arabidopsis and Brassica. Journal of Cell
Science, 1462–1467.
King IP, Morgan WG, Armstead IP, Harper JA, Hayward MD, Bollard A, Nash JV, Foster JW,
Thomas HM.1998. Introgression mapping in the grasses. I. Introgression of Festuca pratensis
chromosomes and chromosome segments into Lolium perenne. Heredity 81, 462–467.
SybengaJ.1999. what makes homologous chromosomes find each other in meiosis? A review and
a hypothesis. Chromosoma 108,209–219.