Asexual Reproduction & MitosisNotes

Asexual Reproduction

• Definition: one parent produces genetically identical offspring

• Advantages: – Can produce offspring w/o a mate– Many offspring in short time

• Disadvantages:– No variation in offspring– No adaptation to new/changing environments

Asexual Reproduction

What kinds/types of reproduction are asexual?

1. Budding - a new individual grows on a ‘parent’Example: hydra, yeast

Asexual Reproduction

What kinds of reproduction are asexual?

2. Binary Fission - a ‘parent individual’ splits into two independent organismsExample: bacteria

Asexual Reproduction

What kinds of reproduction are asexual?

3. Regeneration - fragments of the ‘parent’ can grow into new organisms

Example: starfish, planarian

Asexual Reproduction

What kinds of reproduction are asexual?

4. Parthenogenesis - production of offspring from unfertilized eggs

Asexual Reproduction

What kinds of reproduction are asexual?

5. Vegetative reproduction - occurs in plantsNew plants rise w/o the production of seeds

or spores

Mitosis

• Makes two cells that are genetically identical to each other

• Purpose? – growth and repair

Chromosomes-passed on from one generation to the next-genetic material composed of genes which

are made up of DNA– Only visible during cell division– Found in the nucleus– Condensed DNA

How DNA forms chromosomes

Chromatin

• Chromatin – uncondensed DNA; appears very “stringy”– Form of DNA between cell divisions

Parts of a Chromosome• Sister chromatids: identical copies of a chromosome

– Made during the S phase of the cell cycle

• Centromere: holds two sister chromatids together

The Cell Cycle

The Cell Cycle

• Interphase: – G1 phase: cell growth– S phase: DNA is replicated/copied– G2 phase: more cell growth

• Mitotic Phase:– Mitosis/Cell Division– Cytokinesis (division of cytoplasm)

Mitosis

(Figure 12.6 in your book)

Centrosomes

chromatin -uncondensedchromosomes

G2 of Interphase Prophase

-sister chromatids/chromosomes-nuclear envelope breaks down

-mitotic spindle

Metaphase

-metaphase plate

AnaphaseTelophase&

Cytokinesis

-chromosomes pull apart

-cleavage furrow

-nuclear envelope reforms

Chromosomes move to middle

Mitosis

Prophase

Metaphase

Anaphase

Telophase

Prophase of Mitosis

• Chromatin coils up into visible chromosomes

• Centrioles migrate to opposite ends• Nuclear envelope and nucleolus break down• Centromere of chromosome starts to attach

to spindle fibers

Metaphase of Mitosis

• Chromosomes line up in the middle of the cell

Anaphase of Mitosis

• Spindle fibers contract (shorten)• Chromosomes are pulled apart• Sister chromatids move to opposite poles

Telophase of Mitosis

• Chromosomes gather at opposite poles• Nuclear envelope starts to reform

Cytokinesis• Division of the cytoplasm

– Plant Cells: cell plate is formed cell wall– Animal Cells: cleavage furrow formed

Summary of Mitosis• Start with 1 parent cell and ends with 2 daughter

cells• 2 daughter cells are formed that are genetically

identical to the parent cell• Occurs in somatic cells (aka, body cells)• Functions in growth and repair of cells

Virtual Animation of Mitosis

• Check out this site:Virtual Mitosis Animation

Cell Cycle Regulation• Cyclin – a group of proteins that regulates

the timing of the cell cycle– Controls when cells go from G1 to S phase

– Controls when cells go from S to G2 phase

– Controls when cells go from G2 to M phase

Uncontrolled Cell Growth • Cancer – abnormally rapid cell division• Cells of the tumor may break lose and spread or

metastasize through the body• May be caused by radiation, pollution, bad luck, viral

exposure• Many cancer cells have a mutation/defect in gene p53

(gene that normally tells the cell to wait until all chromosomes have been replicated before proceeding to mitosis)