MEIOSIS

Meiosis is a special type of cell division that produces cells having only one set of genetic information. The process involves a specialized pair of cell divisions that reduce the chromosome number from diploid to haploid.

DIPLOID – contains two copies of each chromosome.HAPLOID – contain only one of each chromosome.

GAMETOGENESIS – a cellular process that generates sex cells or gametes.

Male – a process called spermatogenesis that produces sperm cellsFemale – a process called oogenesis that produces egg cells

ZYGOTE – the product of sperm and egg cells fusion.

THE PROCESS OF MEIOSIS

MEIOSIS IPROPHASE I

During this process, the cell prepares itself for division. The DNA coils and thickens into chromosomes, the nucleoli disappear, the nuclear membrane disintegrates and the spindle begins to form.

Synapsis – a very important event occurs during this phase. During this, homologous sets of chromosomes join together or synapse. This is followed by an actual physical exchange of genetic material via crossing over that leads to recombination.CHIASMATA – the chromosomes at this stage are thicker and shorter. The points of exchange of genetic materials are marked by the formation of this structures.

METAPHASE I

It is characterized by the alignment of the synapsed pair of homologous chromosomes at the equator of the cell. The attachment of the centromere of each chromosome to the spindle makes this movement possible.

ANAPHASE I

In this phase the homologous chromosomes separate. The two members of each pair of homologous chromosomes move away from each other toward opposite poles.

TELOPHASE I

It is characterized by changes that may be described as prophase in reverse. Cytokinesis then divides the cytoplasm into two separate cells.

MEIOSIS IIPROPHASE II

The nuclear membrane disintegrates, nucleoli disappear and the spindle begins to form. Synapsis and crossing over do not occur during this phase.

METAPHASE II

The chromosomes, which are attached by their centromeres to the spindle, align at the equator of the cell. Each chromosome moves as a separate unit because homologous pairs of chromosomes are no longer together.

ANAPHASE II

The centromere of each chromosome splits in two. Then, the chromatids, now called daughter chromosomes, move to the two opposite poles.

TELOPHASE II

New nuclear membranes form, the chromosomes uncoil, the nucleoli reform, and the spindles disappear. Cytokinesis occurs and this stage is followed by differentation of the daughter cells to become gametes-either sperm or egg cells.

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Rezlie B. Cabajes