5. Meiosis is a type of cell division occur only in eukaryote
They are also called as Reduction division
Diploid(2n) Haploid(n)
Two stages in meiosis: meiosis I and meiosis II
The two different sex cells are: sperm and egg
Sex cells produce from germ cells
6. Gametes are haploid
The fusion of gamete lead to production of zygote
Zygote attaining maturity capable of dividing in to
daughter cells
In plants, meiosis is observed after spore production whereas in
animals meiosis take place during gamete formation
Meiosis is similar to mitosis but there is a significant difference
Meiosis consist of two type division:
•Heterotypic division
•Homotypic division
7. Meiosis was discovered and described for the first time
in sea urchin eggs , German biologist Oscar Hertwig,1876
At the level of chromosomes, by the Belgian
zoologist Edouard Van in Ascaris roundworm eggs,1883
The significance of meiosis for reproduction and
inheritance, by German biologist August Weismann, 1890
8. Noted that two cell divisions were necessary to
transform one diploid cell into four haploid cells if the
number of chromosomes had to be maintained
In 1911 the American geneticist Thomas Hunt
Morgan detected crossovers in meiosis in the fruit
fly Drosophilla Melanogaster
This helped to establish that genetic traits are
transmitted on chromosomes.
9. The term meiosis (originally spelled "maiosis")
was introduced to biology by J.B. Farmer and J.E.S
Moore in 1905
It is derived from a Greek word , meaning
'lessening'
10.
11. After chromosomes duplicate, two divisions follow
Meiosis I (reduction division)
Meiosis II (equational division)
12. The parent cell or the dividing cell undergoes a
preparatory phase, known as interphase
The parent cell synthesizes more DNA and proteins,
increasing the overall size and mass of the cell
The dividing cell duplicates or doubles its
chromosomes
13. In animal cells, Outside the nucleus there are two
centrosomes each containing a pair of centrioles
The two centrosomes are produced by the duplication
of single centrosomes during premeiotic interphase.
The centrosomes serve as a microtubule organizing
centers (MTOCs)
Microtubules readily extend from centrosomes forming
an aster
Plant cells do not have centrosomes
14.
15. Prophase I Metaphase I Anaphase I Telophase I and
Cytokinesis
Centrosome
(with centriole pair)
Sister
chromatids
Chiasmata
Spindle
Homologous
chromosomes
Fragments
of nuclear
envelope
Duplicated homologous
chromosomes (red and blue)
pair and exchange segments;
2n 6 in this example.
Centromere
(with kinetochores)
Metaphase
plate
Microtubule
attached to
kinetochore
Chromosomes line up
by homologous pairs.
Sister chromatids
remain attached
Homologous
chromosomes
separate
Each pair of homologous
chromosomes separates.
Cleavage
furrow
Two haploid
cells form; each
chromosome
still consists
of two sister
chromatids.
16. (a)Prophase I:
The chromosomes have
already duplicated and they
coil and become shorter and
thicker.
The duplicated homologous
chromosomes pair, and
crossing-over occurs
17. Crossing–over is the process that can give rise to
genetic recombination
The sites of crossing over are seen as
crisscrossed non-sister chromatids and are called as
chiasmata
Prophase I is divided into five phases:
Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis
18. 1) LEPTOTENE[THIN -THREADSTAGE]
Chromosomes starts to condense
Homologous dyads find each other and align
themselves from end to end with the aid of an axial
element.
19. 2) ZYGOTENE[YOKE-THREAD STAGE]
Homologues chromosomes become closely
associated to form pairs of chromosome
It is known as synapsis
Paired homologous chromosome join with thick
protein containing synaptonemal Complex (SC)
20. 3) PACHYTENE[THICK-THREAD STAGE]
Crossing over take place between pairs of
homologous chromosome to form chiasmata
There represent point where DNA recombination
is occurring
The steps in recombining DNA continue to the end
of pachytene
21. 4) DIPLOTENE[DOUBLE-THREAD STAGE]
Homologous chromosome start to separate but
remain attached to chiasmata
DNA recombination is complete
The SC begins to breakdown
At first chiasmata are located at the sites of the
recombination nodules, But later they migrate towards
the end of the chromatids
22. 5) DIAKINESIS
Homologous chromosome continue to separate, and
chiasmata move to the end of chromosomes
In some organisms, the chromosomes decondense
and begin to be transcribed for a time
24. (b)Metaphase I
The pairs of homologous chromosomes,
as tightly coiled and condensed
It arranged on a plane equidistant from the
poles called the metaphase plate.
Spindle fibers from one pole of the cell
attach to one chromosome of each pair
Spindle fibers from the opposite pole
attach to homologous chromosome.
25. (C)Anaphase I
In anaphase I, pairs of
homologous chromosomes
separate
One chromosome moves
toward each pole, guided by the
spindle apparatus
Sister chromatids remain
attached at the Centromere and
move towards the pole
26. (d) Telophase I and Cytokinesis
In the beginning of telophase I, each half
of the cell has a haploid set of chromosomes;
each chromosome still consists of two sister
chromatids
Nuclear envelope reforms around each
chromosome set, the spindle disappears, and
cytokinesis follows.
Cytokinesis usually occurs
simultaneously, forming two haploid
daughter cells
27. In animal cells, a cleavage furrow forms; in plant
cells, a cell plate forms
No chromosome replication occurs between the
end of meiosis I and the beginning of meiosis II
because the chromosomes are already replicated
28.
29. Division in meiosis II also occurs as four phases
Prophase II
Metaphase II
Anaphase II
Telophase II and cytokinesis
Meiosis II is very similar to mitosis
30. Prophase II Metaphase II Anaphase II Telophase II and
Cytokinesis
Sister chromatids
separate
Haploid daughter
cells forming
During another round of cell division, the sister chromatids finally separate;
four haploid daughter cells result, containing unduplicated chromosomes.
31. (a)Prophase II
The nuclear envelope breaks down and
the spindle apparatus forms.
Here the centrioles duplicate
occurs by the separation of two members
of the pair, then the formation of a daughter
centrioles perpendicular to each original
centriole
The two pairs of centrioles separate in to
two centrosomes
32. (b) Metaphase II
In metaphase II, the sister chromatids are
arranged at the metaphase plate
Because of crossing over in meiosis I, the
two sister chromatids of each chromosome
are no longer genetically identical
The kinetochores of sister chromatids
attach to microtubules extending from
opposite poles
33. (c)Anaphase I:
The centromeres separate
The two chromatids of each chromosome
move to opposite poles on the spindle
The separated chromatids are now called
as chromosomes
34. (d)Telophase II
A nuclear envelope forms around each set of
chromosomes
Cytokinesis take place, producing four daughter
cells, each with a haploid set of chromosomes because
of crossing-over
Some chromosomes have recombined segments of
original parental chromosomes.
42. Meiosis facilitates stable sexual reproduction.
If there is no meiosis, the chromosome number is
doubled. This would result in the formation of
abnormal forms.
Constant number of chromosome in a given
species is maintained by meiosis
During crossing over, the hereditary factors from
female and male parent get mixed. This can lead to
the genetical variation among the species
43. Cooper, G. M., & Hausman, R. E. 2009. The cell: a
molecular approach. Washington, D.C., ASM Press.
Lodish,Berk,Kaiser,Kreiger,Scott,Bretscher,Ploegh,Matsu
daura,6thedition,Molecular Cell Biology.
Albert,Johnson,Lewis,Raff,Roberts,Walton,5thedition,The
Molecular Biology Of The Cell
Gerald Karp, Cell Biology, 6thedition, John Wiley &
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