Transcript Cell division

Cell division
All cells arise from other cells
A cells life cycle is an alternation
between Interphase and mitosis
Interphase

is an active period where there are
many
cell

biochemical reactions
growth
DNA
transcription
DNA
replication
spans most of the life of the cell
Cell division
Mitosis

is the process of dividing one cell
into two cells which each has the
same number of chromosomes as
the parent cell

during the first part of mitosis the
chromosomes condense
and become visible
in the light microscope
they
are two copies
of the original
chromosome
Cell division

the chromosomes become
attached to microtubules and align
themselves in the middle of the cell

each chromatid is drawn by the
microtubules to the opposite ends of
the cell

the cytoplasm is then divided in
two in the middle and a nucleus
forms in both the cells

two new cells have formed that
have genetically identical nuclei
Cell division
Gametes (sex cells) are haploid.
A haploid cell has only one copy of
each chromosome.
It is said to have n number of
chromosomes
All cells except gametes are
diploid.
A diploid cell has two copies of
each chromosome.
It is said to have 2n number of
chromosomes
Cell division
In mitosis one 2n cell divides into
two 2n cells
One diploid
2n
cell
2n
2n
Two diploid cells with
genetically identical nuclei
Cell division
Karyotype is an individuals
particular array of chromosomes.

A normal human karyotype
consists of 46 (2n) chromosomes
or in other words 23 (n) pairs.
Cell division
Meiosis

is a reduction division

a diploid cell divides into four
haploid cells

this involves two rounds of
nuclear divisions
2n
(DNA replication)
Meiosis I
2n
2n
Meiosis II
n
n
n
n
Cell division
Meiosis I
During this stage the double
chromosomes form pairs
Chromosomes #2 Chromosomes #3
from father
from mother
One double chromosome of
each pair can go to either daughter
cell
Cell division
Meiosis II
During this stage the double
chromosomes divide with one part
going into each cell
One part of each
chromosome can go
to either daughter
cell
n
n
Cell division
Meiosis II
Non-disjunction can lead to
changes in chromosome number
One chromosome
does not let go of
both chromatides
and stays
together
n plus an extra
chromosome
n minus one
chromosome
Cell division
Explain how the movement of
chromosomes during meiosis
can give rise to genetic variety in
the resulting haploid cells?
A cell with n = 2 can have how
many different combinations?
A cell with n = 3 can have how
many different combinations?
Meiosis - Mitosis
Cell division
Interphase precedes mitosis and
the doubling of the genetic
material has taken place, through
replication.
Centrioles are also replicated.
Mitosis is divided into four main
phases:
Prophase - metaphase anaphase - telophase
Followed by
Cytokinesis: it is the
cleavage of the cytoplasm and
the formation of new cell
membranes.
Cell division
In plant cells
There are no centrioles
(centrosomes) but still a mitotic
spindle forms.
During cytokinesis the rigid cell
wall prevents the pinching that
happens in animal cells.
Instead membrane
components assemble in the
interior and a cell plate grows
outward until it fuses with the cell
membrane.
Cellulose is the laid down along
the new membranes.