Slides in this set
A brief introduction...
· There are two types of cell division : mitosis and meiosis.
Mitosis is the process of cells dividing for growth and repair,
whilst meiosis is the cell division needed to make sex cells.
Both are essential for life, and the differences in how they
divide is what causes genetic stability and genetic variation in
This is a diagram of the cell cycle.
The part of the cycle where the cell
actually divides is only a small part
of the cycle : the rest is taken up by
interphase. Interphase is split into 3
sub-phases: G1, S and G2. G1 and
G2 stand for Gap Phase 1 and Gap
Phase 2. During these phases the
cell grows and synthesises proteins,
and organelles. S stands for
synthesis. This is where the cell
replicates its DNA, ready for
division. M is the symbol for
their role in cell division
· Chromosomes are made of DNA, protein and a small amount of
RNA. It is found in a single strand running the length of each
· It's only as division starts that chromosomes become visible.
· Shortly before division begins each DNA molecule copies itself. The
single strand inside each chromosome becomes 2 identical strands,
which are now called chromatids. They are joined together by the
centromere. (sister chromatids)
· Chromosomes are found in homologous pairs. Humans have 23
pairs (therefore, 46 chromosomes).
· The total number of chromosomes is called the diploid number. Sex
cells have half the number of chromosomes, and this is called the
haploid number (human gametes have 23 chromosomes).…read more
· This type of cell division
takes place for growth and
· It is also the basis for
asexual reproduction and
cloning, meaning it
· It produces 2 daughter
cells. These are genetically
identical to each other,
and to the parent cell.
· The process by which a
cell divides, the Cell Cycle,
has 5 main stages.....…read more
Stage 1: Interphase
· Interphase isn't technically a part of
mitosis or meiosis. It is best thought of
as the "preparation phase".
· This phase spans over 95% of the cell
· This is where the cell grows and
developes. Organelles are synthesised,
DNA is replicated.
· This means that the cell is in a state of
high metabolic activity, therefore ATP is
needed. This is why the common name
"resting phase" is an inaccurate
· In this phase, the chromosomes are
invisible, since the chromatin is
dispersed through the nucleus.…read more