Anatomy of a Chromosome
p -arm
centromere
q-arm
chromatids
telomere
• Centromere - point
where sister
chromatids are joined
together
• P=short arm; upward
• Q=long arm;
downward
• Telomere-tips of
chromosome
How is a karyotype
prepared?
- A sample of cells is
allowed to reproduce
- A chemical called
colchicine is added
to stop the cell
division
during
http://www.mwit.ac.th/~bio/assets/karyotype_m
metaphase.
utation.swf
- The resulting cells are placed in a solution that causes
the cell membranes to rupture.
- The chromosomes are stained and photographed.
- The chromosomes may then be cut out of the
photograph and arranged by homologous pairs.
What are homologous chromosomes?
- matching pairs of chromosomes -similar in size and
carrying information for the same genes
- They are not identical (i.e. non-sister chromatids)
-Sex chromosome XY pair is NOT a homologous pair
as Y is too short
-Non-sex chromosomes are called autosomes
Asexual Reproduction
and
Mitosis
Asexual Reproduction
– New individual is produced from a single parent by
cell division (i.e. without the use of sex cells)
Hydra asexually
reproduce by
budding
Female aphids give birth to
genetically identical female
offsprings
Strawberry runners
- Offsprings are genetically identical to one another
and to the parent
Asexual reproduction
Advantages
• Parent organism does
not have to seek out
mate
• No specialized mating
behaviours nor
anatomy required
Disadvantages
• Low or no genetic diversity
• Entire population of
identical offspring can be
wiped out in case of
environmental changes
(e.g. diseases, competitor,
volcanic eruptions etc.)
The cell cycle
• Most of the cells life is
spent in Interphase
– Obtaining energy
– Synthesizing
products
– Repairing damage
• G1 - Rapid Growth
• S - DNA Synthesis &
Replication
• G2 - Centrioles
replicate in
preparation for
cell division
Interphase = G1 growth phase + G2 growth
phase and S phase
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Mitosis Overview
Mitosis
(mitos = “thread” in Greek)
- A process that ensures genetically
identical cells
- Only occurs in eukaryotic, somatic
cells (i.e. non-sex cells)
- Before cell division, cells MUST
undergo DNA replication
- This creates 2 complete sets of
DNA; one set for each cell after the
division
MITOSIS
Occur in both plant and animal cells
Has 4 stages
1. Prophase (Beginning phase)
2. Metaphase (Middle phase)
3. Anaphase (second last phase)
4. Telophase (last phase)
Thus, PMAT for short
NOTE: Interphase is not a phase of mitosis, it’s
a phase in cell cycle. However, it is usually
mentioned in mitosis (thus, IPMAT)
Prophase of mitosis
• Nuclear membrane fades
• Chromosomes condense – can see sister
chromatids and centromere
• Spindle fibre forms
• Centrioles start to move to opposite poles
Animal Cell
Spindle fibers
Plant Cell
Metaphase of mitosis
- Chromosomes line up at the equatorial
plate (middle) of the cell
- Each chromatid is attached to spindle
fibres at centromere
Animal Cell
Plant Cell
Anaphase of mitosis
- Proteins that hold pair of chromosomes at centromere
break apart
- Spindle fibres has been stretched like an elastic band
now pulling a chromatid (one chromosome of a pair)
toward each end of the cell
Animal Cell
Plant Cell
Telophase of mitosis
- Spindle fibres dissolve
- Nuclear membrane reforms around chromosomes
of the 2 new nuclei
- Chromosomes relax into chromatins
Animal Cell
Plant Cell
Cytokinesis
- The nucleus has now been copied
- Cell next undergoes cytokinesis:
- Cytoplasm and organelles are copied
before telophase completes
- Proteins around middle of the cell starts to
contract, pinching the cell membrane
inward
- Create 2 daughter cells
- Cytokinesis completes cell division
- Cell then enter into its resting phase:
interphase (G1, S and G2)
Cytokinesis in plant cell
- Rigid cell wall, can’t pinch membrane the way
animal cell does
- Instead: small vesicles (produced by Golgi
body) line up between 2 new nuclei forming a
cell plate
- Cell plate grows outward and reaches the old
cell wall
- New cell membrane is formed
Result of mitosis
- A parent cell becomes 2 new,
genetically identical daughter
cells
- Each cell has the same set of
chromosomes as the parent cells
- WATCH THIS VIDEO: Recap of mitosis
http://www.youtube.com/watch?v=VGV3fvuZYI
- Complete mitosis exit quiz 10-15 min
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Mitosis Exit quiz
10-15 minutes