CELL DIVISION

CELL DIVISION

 

     CELL CYCLE

Cell Cycle : Sequential events occur in the life of a dividing cell is called cell cycle.

 

Interphase: The stage between two successive cell divisions called interphase.

 

S-phase : It is a phase of the cell cycle in which DNA replication occurs.

 

Karyokinesis : Division of nucleus into the two daughter nuclei is called karyokinesis.

 

Cytokinesis : Division of cytoplasm to form two daughter cells is called cytokinesis.

 

Amitosis : Cell division by simple cleavage of the nucleus and division of the cytoplasm without spindle formation or appearance of chromosomes is called amitosis.

 

Mitosis : It  is a type of cell division in which a parent cell divides to form two daughter cells which are clone to the parent cell. Since it occurs into the somatic cells so it is also called somatic cell division, it is also called equational division since it maintains the number of chromosome in daughter cells.

 

Karyotype / Karyogram: It is the arrangement of chromosome in homologous pair and numbered sequence to determine the chromosome complement of an individual is called karyotype or karyogram.

 

Condensation: Reorganisation of the long and thin chromatin strands into compact short and thick chromosomes are called condensation.

 

Centromere : The point of attachment between two sister chromatids of a chromosome is called the centromere. It is also called a primary constriction.

 

Meiosis: It is a type of cell division in which a parent cell divides to form four daughter cells. Since it occurs into the germ cells so it is also called germ cell division, it is also called reductional division since the number of a chromosome gets reduce to half in daughter cells.

 

Metaphasic plate: During Metaphase, all the chromosomes lie at the equatorial plane of the cell. This is called the metaphase plate.

 

Terminalization: Shifting of chiasma to the ends of the chromosome is called terminalization, it occurs during diakinesis stage of meiosis-I.

 

Interkinesis: The short resting phase between cytokinesis-I and meiosis-II is called interkinesis

 

Kinetochore fibres: The Spindle fibres present between centriole and centromere is called as kinetochore fibres.

 

Polar fibres: The spindle fibres present between two opposite centrioles are called polar fibres.

 

Cell plate: The formation of the new cell wall in plant cell begins with the formation of a simple precursor, called the 'cell-plate' which represents the middle lamella between the walls of two adjacent cells.

 

Necrosis : Death of  cells because of any injury is called necrosis.

 

Apoptosis : It is a programmed cell death where cells undergo "cellular suicide" when they receive certain signals. It is a controlled process.

 

Meiocytes : The cells which undergo meiosis are termed as meiocytes.

 

Synopsis: The pairing of non-sister chromatids of homologous chromosomes during the meiosis is called synapsis.

 

Bivalent: The pair of a homologous chromosome is called bivalent.

 

Tetrad : All the four chromatids of bivalent i.e. homologous chromosome is called tetrad.

 

Chiasma / Chiasmata: The point on the chromosome where crossing over takes place is called chiasma (single point) or chiasmata (multiple points). These points appear like a cross (X).

 

Crossing over / Recombination: During prophase-I of meiosis-I the non-sister  Chromatids of homologous chromosome cross each other and break at chiasma these broken segments are exchanged between non-sister chromatids of a homologous chromosome are called crossing over or recombination.

 

Desynapsis : The separation of homologous chromosomes in the diplotene stage of meiotic prophase is called desynapsis.

 

Disjunction : During  Anaphase I,  homologous chromosomes are pulled away from each other and carried towards opposite poles by spindle apparatus. This is called a disjunction.

 

Terminalization : In diakinesis, the chiasmata beings to move along the length of chromosomes from the centromere towards the ends of chromosomes. The displacement of Chiasmata is termed as terminalization.

 

Interkinesis : In many cases,  daughter cells formed during Meiosis I,  pass through a short resting phase or interphase called interkinesis.

 

Homotypic division: Cell division in which the number of chromosome in the daughter cell equals to the number of chromosomes in the parent cell is called homotypic division.

 

Heterotypic division: Cell division in which the number of chromosome in the daughter cell does not equal to the number of chromosomes in parent cell is called heterotypic division.

 

Monstrosities : Normally, The meiotic division produces gametes. If it is absent, the number of chromosomes would double or quadruple resulting in the formation of monstrosities (abnormal forms).