Mental health articles

Meiosis Definition Meiosis is a process of nuclear division accompanying
cell division that produces four separate nuclei for four new daughter cells which are haploid, that is, carry half the number of chromosomes of the parent cell’s full diploid chromosomal complement. Meiosis bear many similarities to  mitosis in terms of the phases of its cell-division, which are: 1) prophase I, 2) metaphase I, 3) anaphase I, 4) telophase I, 5) prophase
II, 6) metaphase II, 7) anaphase II, and 8) telophase
II.

However, during meiosis there is an exchange of genetic information between homologous chromosomes, which does not occur during mitosis. During prophase I, as the duplicated chromosomes condense
into bar-like bodies, joined at the centromere, they are aligned laterally with their duplicated homologous chromosome, called synapsis. This alignment
is called a bivalent. During late prophase, the ends of the aligned homologous chromosomes are often exchanged at a point called a cross-over, of which there can be many between any set of homologous chromosomal arms. This process is called  recombination.
There can be many recombinations along a chromosome,
although in general, there are fewer recombinations
near the centromere than there are towards the
ends of the chromosomal arms. At the end of prophase,crossover points called chiasmata still exist. During metaphase I, the bivalents are bound to the mitotic spindle, and in anaphase, the chiasmata disappear as
the homologous chromosomes are pulled apart to their
respective poles, taking along recombinant chromosomal
arms. In telophase I, a nuclear envelope may or may not form, as a second round of division is about to be initiated. At this point in the division, each daughter cell has 46 chromosomes, all of which are non-identical,
homologous chromosomes joined at their similar centromeres. Prophase II is short, and it occurs before the chromosomes have had a chance to replicated or enter an additional cell cycle. In metaphase II
the chromosomes align on the metaphase plate, and the
two homologous chromosomes, looking much like sister
chromatids, are pulled apart to their respective poles
in anaphase II.
In metaphase II, nuclear envelopes form around the cells, each with a haploid complement of 23 chromosomes. From one diploid parent cell, four haploid daughter cells have arisen.

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