Anatomy of a Chromosome

• Centromere - point where sister chromatids are joined together

• P=short arm; upward• Q=long arm;

downward• Telomere-tips of

chromosome

p -arm

centromere

q-arm

telomerechromatids

How is a karyotype prepared?

- 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.

- A sample of cells is allowed to reproduce- A chemical called colchicine is added to stop the cell division during metaphase.

http://www.mwit.ac.th/~bio/assets/karyotype_mutation.swf

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)

Female aphids give birth to genetically identical female offsprings

Hydra asexually reproduce by budding

Strawberry runners

- Offsprings are genetically identical to one another and to the parent

Asexual reproduction

• Parent organism does not have to seek out mate

• No specialized mating behaviours nor anatomy required

Advantages 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

MITOSISOccur 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 Plant CellSpindle fibers

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=VGV3fv-uZYI

- Complete mitosis exit quiz 10-15 min

Plant Mitosis -- ReviewInterphase

                                                

            

Prophase

                                               

             

Metaphase

                                                

            

Anaphase

                                               

             

Telophase

                                                

            

Interphase

                                               

             

Animal Mitosis -- Review

Interphase

                                              

              

Prophase

                                             

               

Metaphase

                                              

              

Anaphase

                                             

               

Telophase

                                              

              

Interphase

                                             

               

Mitosis Exit quiz

10-15 minutes