CHAPTER 5: CELL DIVISION

Why produce new cells?

• Cells:• Wear out after some time• Get damaged • Grow old naturally and die

• Therefore organisms need to produce new cells to :• replace those cells that are worn out, damaged or dead• Perpetuate their own species either by asexual or sexual

reproduction

Types of cells division

• Two types of cell division:a) Mitosis

b) Meiosis

Mitosis

Cell divide (by mitosis) to supply new daughter cells that are identical to parents cells

Repair of tissues:Identical new cells to replace worn out or damaged cells. Skin cells and cells lining gut constantly die and are replaced

Growth : More cells for growth

Asexual reproduction:Binary fissionBuddingVegetative reproduction

SignificanceCell division

•Cells wear out•Cells get damaged•Cells grow old and die

Organisms grow

Reasons

Need more cells for reproduction

Mitosis

• Mitosis produced new cells that genetically identical to their parents to:

1. Continue with the specific cell functions of their parent cells within a particular tissue

2. Avoid disrupting the stable internal environment of life or its processes

3. Produce offspring that have complete functions of an adult organism to ensure the survival of that species

CELL DIVISION : MITOSIS

Organization of phases and subphases in a cell cycle

Cell cycle

Interphase

M Phase

G1

S

G2

Mitosis

Cytokinesis

Prophase

Metaphase

Anaphase

Telophase

EFFECTS OF UNCONTROLLED MITOSIS IN LIVING THING

Mutation

• Mutation : the change in the DNA structure of the cell• Lead to uncontrolled mitosis – tumors• Tumors :• Have no function• Interfere with the normal activity of surrounding cells• Two types :• Benign tumors• Malignant tumors

Benign tumors

• Inactive, relatively harmless• Remain at its original site & do not spread to other parts

of the body• Some may progress to become cancerous tumors if left

untreated• Usually treated by surgery, radiation, chemotherapy

Benign Tumors

Malignant tumors

APPLICATION OF KNOWLEDGE ON MITOSIS IN CLONING

Application of knowledge on mitosis in cloning

Cloning of microbes

Cell culture

Fermenters

Cloning of plants

Tissue culture

Cloning of animals

Therapeutic cloning

Reproductive cloning

Embryo cloningSomatic cell

cloning

Tissue Culture

Callus

Embryo cloning

Somatic Cell Cloning

Dolly

MEIOSIS

Species Diploid chromosomal number of somatic cells (2n)

Haploid chromosomal number (n)

Fruit fly (Drosophila melanogaster)

8 4

House fly (Musca domestica)

12 6

Corn (Zea mays) 20 10

Onion (Allium sp.) 32 16

Human (Homo sapiens) 46 23

Chicken (Gallus domesticus)

78 39

House mouse (Mus muscullus)

40 20

Diploid (2n=6)Male parent

Diploid (2n=6)Female parent

Diploid (2n=6)offspring

Embryo(2n)

Haploid (n = 3) sperm

Haploid (n = 3) egg

Diploid zygote(2n = 6)

Autosomes & Sex Chromosomes

Chromosomes

• Two types of chromosomes:• Autosomes• Sex chromosomes

SEX AUTOSOMES SEX CHROMOSOMES

SOMATIC CELL

Male 44 / 22 pairs XY 44 + XY

Female 44 / 22 pairs XX 44 + XX

Down’s Syndrome

• Caused by:• Improper separation of the chromosomes• Non-disjunction

Down’s Syndrome

MITOSIS VS MEIOSIS

REVISION

Meiosis

P1 : The crossing over process occur during prophase

P2 : The tetrad (sister chromatids) are formed

Prophase 1

Anaphase 1

Crossing over

P1 : (the crossing over results) in exchange of genetic material between non sister chromatids

P2 : (which results in) the formation of new combinations of alleles on a chromosome // causes variation

Down’s Syndrome