Cell Division

What is cell division? Cell division is a process by which a mother cell

divides into two or more daughter cells. It refers to the replication of cells from mother cell

to daughter cells. Replication means to produce of the same kind.

Cell Division

Mitosis

Meiosis

Mitosis: A type of cell division that results in two daughter cell each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth. It occurs in somatic cells.

Two types

Meiosis: A type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.

Mitosis cell division completes with four different steps:

Prophase Metaphase Anaphase Telophase

1. Prophase Chromosomes become thicken, shorten and

become visible. Centrioles move to the opposite sides of the

nucleus. Nucleolus disappears. Nuclear membrane disintegrate.

Chromosomes meet in the middle. Chromosomes arrange at equator of cell. Become attached to spindle fibres by centromeres. Homologous chromosomes do not associate.

2. Metaphase

Chromosomes get pulled apart. Spindle fibres contract pulling chromatids

to the opposite poles of the cells.

3. Anaphase

Chromosomes uncoil. Spindle fibres disintegrate. Centrioles replicate. Nuclear membrane forms. Cell divides.

4. Telophase

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Mitosis

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MeiosisMeiosis is consist of two cell divisions: Meiosis I (reduction phase) Meiosis II

Meiosis I: Prophase I The prophase stage of meiosis I is relatively

long and can be subdivided into five stages: Leptotene

ZygotenePachytene

DiploteneDiakinesis

Prophase I: Leptotene The chromosomes become visible as they

start to condense.

Prophase I: ZygoteneHomologous chromosomes align directly opposite each other and are held together at several points along their length.

Leptotene

Zygotene

Prophase I: PachyteneEach pair of homologous chromosomes becomes tightly coiled.

Prophase I: DiploteneThe homologous recombinant chromosomesnow begin to separate but remain attachedat the points where crossing over hasoccurred.

Pachytene

Diplotene

Prophase I: DiakinesisSeparation of the homologous chromosome pairs proceeds as the chromosomes become maximally condensed.

Metaphase IThe nuclear membrane disappears and the chromosomes become aligned on the equatorial plane of the cell where they have become attached to the spindle as in metaphase of mitosis.

Diakinesis

Metaphase I

Anaphase IThe chromosomes now separate to opposite poles of the cell as the spindle contracts.

Telophase IEach set of haploid chromosomes has now separated completely to opposite ends of the cell which cleaves into two new daughter gametes, so-called oocytes.

Anaphase I

Telophase I

Meiosis II This is essentially similar to an ordinary mitotic division.Each chromosome, which exists as a pair of chromatids, becomes aligned along the center of the cell and then splits leading to the formation of two new daughter gametes, known as spermatids.

Mitosis Meiosis

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Cell divisio

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Somatic cell

Germ cell

Single division

Two divisions

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