Mitosis
After completing the interphase
(G1Phase, S Phase, G2Phase), cells enter into mitosis for cell division.
Mitosis occurs in somatic cells (non-reproductive cells)
of the body takes place in all types of cells that are not involved in the
production of gametes.
Mitosis is a process where one cell divides into two
identical daughter cells (cell division).
Check out here how cell
division occurs? And what is the cell cycle?
Mitosis produces two diploids (2n) that are genetically
identical to each other and the original parent cell.
Note- When a haploid cell undergoes mitosis cell division, produces two
genetically identical haploid cells. Mitosis cell division can occur
both in diploid and haploid cells.
The different stages of mitosis and cytokinesis define
the Mitotic or M phase cell cycle. The division of the mother cell
into two diploid daughter cells genetically identical to each other.
Know
here what is difference between mitosis and meiosis?
Phases of Mitosis
Mitosis
is involved five phases, these ares-
1.
Prophase
a.
Early Prophase
b.
Late Prophase
2. Prometaphase
3.
Metaphase
4.
Anaphase
a.
Early anaphase
b.
Late anaphase
5.
Telophase
1. Prophase
Prophase is the first phase of mitosis; mitosis begins at prophase.
Prophase
involves two phases; Early prophase
and Late prophase.
Early prophase
Early prophase Mitotic spindle starts to form, the
chromosomes start to condense.
Late prophase
Late prophase Nuclear envelope breaks down and
chromosomes are fully condensed and the nucleolus disappears completely.
2. Prometaphase
In prometaphase, kinetochores (protein complex) appear
at the centromeres and mitotic spindle microtubules attach to kinetochores.
3. Metaphase
1. Microtubules of spindle have attached to
kinetochores.
2. Chromosome lined up on the metaphase plate (midpoint region).
3. End of metaphase centromere doubled. So that each
chromatid has its own centromere.
4. Sister chromatids are pulled; move toward opposite
spindle poles of the cell.
4. Anaphase
Anaphase Involve; Early anaphase and Late anaphase.
Early Anaphase (or Anaphase A)
During early anaphase –
1. Sister chromatids separate.
2. Splitting and separation of centromeres.
3. Movements of two sister chromatids of each pair
toward opposite poles of the cell.
Late anaphase (or Anaphase B)
During late anaphase –
1. Separation of the sister centrosomes to their
opposite poles and remain attached to the spindle fibers by their centromeres.
2. Cytokinesis may begin in which cleavage furrow is
induced by the mitotic spindle during late anaphase.
5. Telophase
1. Chromatids reach the opposite pole.
2. Chromosomes begin to uncoil (rod-like form).
3. Spindle dissolve
4. New nuclear envelope is formed
5. Cytokinesis occurs in which cells split into two
identical daughter cells.
Cytokinesis
Nuclear division or mitosis is followed by cytokinesis.
1. It is the
separation of cytoplasm into two parts.
2. Separation is achieved by cleavage “furrow- a
pinching” of the plasma membrane.
3. Cells splits into two, the result is two separated
genetically identical daughter cells produced.
4. Cytokinesis may begin during late anaphase or
telophase.
Meiosis
Meiosis occurs in the germ cells (produce gametes) of the body. Germ cells undergo meiosis to produce haploid (n) gametes.
Meiosis is the process of cell division that occurs in
the formation of reproduction cells (gamete or sex cell - ova or spermatozoa or
sperm). Meiosis begins with diploid cell in parent cell.
Meiosis produces four haploids (n) daughter cells,
gametes that are genetically unique from each other and the original parent
(germ) cell.
Stages of Meiosis Undergoing meiosis, the cell goes through an interphase stage, in which cells grow in size, chromosomes replicate;
chromosomes of diploid ell double, centriole replicates and check all to ensure
that it is ready to divide.
Meiosis occurs in two successive nuclear divisions-
A. Reduction division (meiosis-l)
B. Equatorial division (meiosis-ll)
A. Meiosis – l
The stages of Meiosis-l are;
a. Prophase- l
b. Metaphase –l
c. Anaphase –l
d. Telophase-l and cytokinesis
a. Prophase- l
1. Chromosomes shorten and thicken
2. Nuclear envelope breaks down and nucleoli disappear
3. Mitotic - spindle appears
4. Centrioles begin to move toward opposite poles
5. Chromosomes become arranged in homologous pairs, this
pairing is called synapsis. At this point, chromosomes ends are attached to the
nuclear envelope. The four chromatids of
each homologous (similar) pair are termed Tetrad.
Crossing over
During meiosis crossing over is an exchange of genetic
material between non-sister chromatids of homologous chromosomes. A portion of
one chromatid may be exchanged with a portion of another chromatid, which results
in “Genetic recombination”.
Formation of new combinations (allelic combinations) of
genes in the daughter cell.
3. Anaphase- l
The homologous pair is pulled to move opposite ends of
the cell by microtubules attached to the centromere.
The sister chromatids of each chromosome remain
attached to one another and centromere don't split and paired chromatids held
by centromere remain together.
4. Telophase- l and Cytokinesis
In this phase when the chromosomes have finished moving
to opposite ends of the cell then it is followed by cytokinesis, result-producing
two daughter cells.
After cytokinesis, the two daughter cells are
genetically different chromosomes after meiosis I.
Interkinesis
Interkinesis is the time between the formation of
daughter cells and the second meiotic division, meiosis-ll.
B. Meiosis-ll
During meiosis II, the sister chromatids within the two
daughter cells separate, forming four new haploid gametes.
a. Prophase –ll
b. Metaphase-ll
c. Anaphase-ll
d. Telophase-ll
a. Prophase–ll
Prophase II is the phase that follows after meiosis-l.
1. The nuclear membrane (nuclear envelope) and nucleolus disintegrate
during prophase II.
2. The spindle fibre is formed,
centrosomes move toward the opposite pole of the cell and the spindle
microtubules begin to capture chromosomes.
b. Metaphase-ll
Chromosomes line up at the
metaphase plate through the facilitation of the spindle fibers.
c. Anaphase-ll
The centromere split and the
attached sister chromatids separate and move toward opposite poles of the cell.
d. Telophase-ll
Nuclear envelope forms around the
four haploid nuclei.
Telophase-ll followed by
cytokinesis, resulting in a produce four genetically dissimilar haploid cells.
Cytokinesis
Cytokinesis produces four haploid
cells that are genetically different haploid cells.
Meiosis-l begins with a diploid starting cell and
ends with 2 haploid numbers of chromosomes, where each chromosome is made up of
two connected sister chromatids.
During meiosis-ll, each of two haploid cells formed
during meiosis- l divide, the sister chromatids are separated and the result is
four haploid gametes that are genetically different from the original diploid
starting cell.
Get here details on the embryonic
origin of tissues or germ layer cells.
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