Transcript Cell Division

Second phase
of growth,
further
synthesis of
organelles
occurs,
chromosomes
start
condensing
Synthesis of DNA, the
DNA of the chromosomes
is replicated
Mitosis
Nuclear division
Cytokinesis
Cytoplasmic
division
First phase of
growth, the cell
grows and develops,
and additional
organelles are
synthesised, the
nucleus directs
protein synthesis.
Interphase
Centriole
Chromosome
is long and thin,
cannot be seen under
the light microscope
Cell synthesizes more
cytoplasm and
organelles,
chromosomes replicate,
cell builds up large
store of energy
Nucleolus
MITOSIS
Prophase
Chromosome
Shortens and condenses,
becomes visible under
the light microscope
Nucleolus
Gradually disappears
Centrioles move towards
opposite poles of the cell
Prophase
Chromatid
Centromere
Prophase
Centriole
Microtubules extend
from here towards the
equator of the cell to
form the spindle
Nuclear membrane
Begins to break down
Sister chromatids
Spindle pole
Metaphase
Spindle fibre
Spindle
equator
Centromere
becomes attached
to a spindle fibre
and moves to the
equatorial plane
Chromosomes line
up at the equator
of the spindle
Anaphase
Daughter
chromosome
Centromere
divides and the
daughter
chromosmes move
to opposite poles
with centromere
leading
Nuclear
membrane
Telophase
Surrounds
daughter
chromosomes
Chromosomes
uncoil and
gradually
become invisible
under light
microscope
Nucleolus
reforms
Division of the cytoplasm
Animal cell
Cell membrane
invaginates at the mid
point of the cell dividing
the cell into two, cells
are diploid (2N) and are
identical to each other
Plant cell
Tiny vesicles
containing cell
wall materials
coalesce to
form the cell
plate
Cell plate
extends
outward to the
cell wall and
separates cell
into two
MEIOSIS
Meiosis I
Prophase I
Pairing of homologous
chromosomes
maternal and paternal
chromosomes come
together and lie close
to each other
Bivalent
Prophase I
Sister chromatids
separate and become
visible, they are held
together by the
centromere
Prophase I
Crossing over occurs
between chromatids
of homologous
chromosomes
Chiasma
Metaphase I
Centromere becomes
attached to individual
spindle fibre
Chromosomes lie at
the equator of the
spindle with
members of each
homologous pair
facing opposite poles
Anaphase I
Members of each
homologous pair
move towards
opposite poles
Telophase I
Nuclear membrane
reforms around the
chromosomes
Cell divides into two
Prophase II
Nuclear membrane
disappearing
Metaphase II
Chromosomes attached to spindle fibres by their
centromere, line up at the equator of the spindle
Anaphase II
Centromeres divide and separate, pulling the sister
chromatids to the opposite poles
Telophase II
Nuclear membrane forms
around the chromosomes
Interphase
Four haploid
(N) daughter
cells are
produced
Comparison between mitosis and meiosis
Mitosis
Pairing of homologous
chromosomes
No
Crossing over
No
Anaphase
Number of
divisions involved
Daughter cells
Occurrence
Sister chromatids
separate during
anaphase
One
Two diploid (2N)
daughter cells, they
are identical
During growth,
asexual
reproduction
Meiosis
Yes
Yes
Homologous chromosomes
separate during anaphase I,
sister chromatids separate
during anaphase II.
Two
Four haploid (N)
daughter cells, they
are non-identical
Production of
gametes for sexual
reproduction
• Clegg C.J., Mackean D.G., Advanced
Biology: principles and applications
• Enger/Ross, Concepts in Biology
CROSSING OVER - exchange of genetic
material between non-sister chromatids
Non-sister
chromatids
overlap
Once overlap,
they break
Join with broken
fragments of nonsister chromatid i.e.
exchange of genetic
material occurs
Crossing over - Chiasma
Chiasmata have two functions:
(1) hold the homologous
chromosomes together as they
move to the equator of the
spindle (2) allow exchange of
genetic materials between
homologous chromosomes giving
rise to genetic variations in the
offspring