Mitosis + Asexual Reproduction

mitosis

* a type of cell division in which two identical daughter cells are formed
* every cell in the body is formed by mitosis except for sperm and egg cells

unicellular organisms use mitosis to:

reproduce

multicellular organisms use mitosis to:

grow and develop, replace worn out cells

chromosomes

* structures that contain DNA
* humans have 46 chromosomes in each body cell

chromosomes ___ prior to cell divison

replicate (duplicate)

chromosomes replicate to form sister ___

chromatid

most of the time the cell is not actively dividing, it is in:

interphase

interphase

a) chromosomes are in the form of chromat__**in**__(DNA is loosely wrapped around the protein - __**in**__visible

b) nickname - “resting phase” (inaccurate because the cell is carrying out normal activities

c) chromosomes replicate

**Asexual Reproduction**

* A single organism makes an identical copy of itself
* Reproduction by **MITOSIS**
* only one parent
* offspring is genetically identical to parent organism

examples of Asexual Reproduction

* binary fission 
* budding
* sporulation
* regeneration 
* vegetative propagation

Advantages of Asexual Reproduciton

* rapid and results in the production of large numbers of offspring
* helps organism reproduce in large numbers when environmental conditions are good

Disatvantages of Asexual Reproduction

* All offspring are genetically identical
* If environment changes, none of the organisms have a different trait that might allow them to survive
* They cannot evolve!

**Binary Fission**

parent organism divides into 2 **equal** parts (ex. bacteria, protists)

**Budding**

parent organism divides into two **UNEQUAL** parts (ex. hydra)

**Sporulation**

* Spores are single, specialized cells produced by mitosis
* Spore germination requires an environment that is warm, has nutrients and moisture

Regeneration

* The ability of an organism to regrow lost body parts
* Regeneration decreases as an animal becomes more complex
* (ex. starfish)

Vegetative Propagation

* A type of regeneration that occurs in plants
* Complete new plants develop from a part of the parent plant (root, stem, leaf)

Examples of vegatative propagation

NATURAL - bulbs, tubers, rhizomes,

MAN-MADE - cuttings, grafing

**Advantages of Vegetative Propagation**

* Produces plants with identical desired characteristics

(Seeds come from two different parents and offspring plant shows different traits)

* Faster
* Higher yields of fruits

Why not become one big cell?

* surface area of the membrane (roadways) could not transport all the food, oxygen, and wastes necessary for the volume of the cell


* the dna library would not be able to serve all the cell’s needs

surface area + volume ratio

cell’s require a large surface area to volume ratio

2 components of cell division

1) nuclear division (mitosis)

2) cytoplasmic division (cytokinesis)

nuclear division (mitosis)

genetic material must be divided so that each cell has a new complete set of chromosomes

cytoplasmic division (cytokenisis)

the contents of the cytoplasm must be divided so that each new cell has a complete set of organelles

phases of mitosis

1. prophase
2. metaphase
3. anaphase
4. telophase

__**p**__rophase

Beginning of mitosis __**p**__repares cell for division

a) nuclear membrane disintegrates; nucleolus dissapears

b) chromosomes coil and contract (thicken) and become visible (chromati__**d**__s) \*\*link the D in chromatids to the D in __**d**__ividing

c) replicated chromosomes are held together by a protein called a __**centromere**__

d) centriole moves to the opposite poles of the cell

e) spindle apparatus forms

__**m**__etaphase

a) replicated chromosomes line up in the __**m**__iddle of the cell

__**a**__naphase

a) chromatids move apart to opposite poles of the cell with the help of spindle fibers

__**t**__elophase

a) chromosomes uncoil, become threadlike (chromatin)

b) spindle disentigrates

c) nuclear membrane, nucleolus reforms

d) __**t**__wo new cells are formed

cytokinesis

* occurs the same time as a telophase
* division of cytoplasm

(cytokinesis) in animal cells:

membrane pinches inward

(cytokinesis) in plant cells:

a cell plate forms

* new membranes and cell walls are formed in the center of the cell to seperate two new cells

mitosis in plant cells:

* plant cells have **no** centrioles


* spindle fibers connect to cell wall

cancer

* uncontrolled cell division
* cancer cells are frequently “immortal”: normal cells divide about 50 times and then die, cancer cells can go on dividing indefinetly if supplied with nutrients
* can produce abnormal cells with an abnormal amount of chromosomes
* use excess nutrients and oxygen so normal cells are deprived
* can spread to other tissues