ASEXUAL REPRODUCTION

ALL CELLS COME FROM PRE-EXISTING CELLS

* when offspring are produced from a single parent, it is called asexual reproduction
* the offspring are identical to the parent!

By cell division, one cell divides to become two. This process is used by some organisms, such as protozoans, to reproduce. In other, multicellular organisms, this process is used to grow in size or to replace tissues.

* when offspring are produced from two parents, it is called sexual reproduction
* the offspring is a combination of the two parents


REMEMBER CYTOLOGY--the study of cells

the nucleus ...

... is the control center ...

... which has the genetic material ...

... which is DNA
(deoxyribonucleic acid)

* lots of DNA when it is bunched up is called a chromosome

CHROMOSOMES = LOTS OF DNA

Chromosomes are only visible during cell division (mitosis) because they coil up. It has one 'arm' (chromatid) until it doubles...then it has two 'arms' (chromatids)

MITOTIC CELL DIVISION

ALL CELLS ARISE FROM OTHER CELLS BY CELL DIVISION. THIS PROCESS INVOLVES BOTH:

1) MITOSIS (duplication of the nucleus)

* this is an orderly series of complex changes in the nucleus
* this involves an EXACT DUPLICATION of the complete set of chromosomes
* also makes sure that these chromosomes are separated into two equal sets
* forms 2 cells identical to the first

2) CYTOPLASMIC DIVISION (cytokinesis)

* when the cytoplasm of the parent cell divides into 2 daughter cells
* also called cytokinesis

***When the process of cell division is uncontrolled, cells keep reproducing... which is called CANCER***

* Mitosis happens in all cells in humans EXCEPT eggs and sperm

Mitosis and Asexual Reproduction

One of my own creations (featuring Mrs. G in her pseudo-British accent), see why a cell must divide when it grows too big.
watch all the basics of mitosis
see the different stages of the cell cycle in this game where you play the role of a cell supervisor
Tim and Moby discuss cell division.
another great PBS site, this shows how cancer (a form of mitosis) spreads through the body

CELL DIVISION

the process by which the nucleus of a cell divides, producing two nuclei with the diploid (2n--2 sets of chromosomes) number of chromosomes

I. INTERPHASE

* in between actual divisions
* the cell grows
* DNA exists as chromatin (a messy plate of spaghetti)
* the DNA duplicates (replicates) so now there are briefly 4 sets (4n); normally there are just 2 (2n)--one from each parent
* the centrioles also replicate (duplicate)

II. PROPHASE

* the DNA starts to condense and form chromosomes--the two halves of the chromosome (each chromatid) are held together at the centromere
* the nuclear membrane that keeps the DNA (now in the form of chromosomes) in the nucleus starts to disappear
* the centrioles start to move towards different ends (or poles) of the cell
* the spindle apparatus (looks like a cage) forms from the framework of the cell around the centrioles (which now are look like stars called 'asters')


III. METAPHASE

* the spindle apparatus is fully formed and the chromosomes attach to it at the centromere
* the chromosomes line up in the middle of the spindle (called the metaphase plate)

IV. ANAPHASE

* the chromosomes separate at the centromere and split apart (chromosomes move away from each other)
* the spindle fibers shorten and pull the chromosomes to each end (aster)

V. TELOPHASE

* the chromosomes have finished moving to the different poles (ends) of the cell
* a new nuclear membrane starts to form around each new COMPLETE set of chromosomes
* the DNA starts to uncoil again to form chromatin


AT THIS POINT, ONLY THE NUCLEUS HAS DIVIDED INTO 2 IDENTICAL NUCLEI...WE STILL HAVE ONLY 1 CELL!

VI. CYTOPLASMIC DIVISION

* after the reformation of the nuclear membrane, the cytoplasm divides
* this make 2 daughter cells that are identical to the parent, but smaller!


Mitosis and Asexual Reproduction

watch all the basics of mitosis
work with cells in different phases of mitosis
made for Regents biology, this is a must see animation/ description of mitosis
another John Kyrk animation, this time, of the process of mitosis
good review of the phases of the cell cycle; a couple of decent mitosis animations
a basic interactive animation of mitosis
fantastic interactive animation of the phases of mitosis

CLONING

* making a duplicate of an organism or one or more of its cells by artificial means
* Dolly the sheep was cloned using nuclear transfer methods (see picture)


COMING SOON...CLONING HUMANS?
MORAL IMPLICATIONS? IS THIS RIGHT?


DIFFERENCES BETWEEN PLANT AND ANIMAL CELL DIVISION

1) in animal cells, centrioles help form the spindle; centrioles are not found in plant cells

2a) in animal cells, cytoplasmic division occurs by the cell pinching in...

2b) in plant cells, a CELL PLATE forms between each new cell, like a cell wall


Mitosis and Asexual Reproduction

cloning, accurately described in this NOVA clip
outstanding reference to what cloning really is; contains a few great click-and-play animations
clone MIMI THE MOUSE!; shown in school, this is a must see for students and parents to show how nuclear transfer (cloning) is carried out
Tim and Moby discuss cloning.

TYPES OF ASEXUAL REPRODUCTION

* carried out by unicellular organisms, many lower animals, and many plants
* asexual reproduction IS mitosis
* offspring are identical to the parents
* the process is usually rapid and results in a large number of offspring
* there are several types of asexual reproduction

1) binary fission

* the equal division of nuclear material and cytoplasm resulting in 2 new organisms
* basically is simple animal cell mitosis
* carried out by paramecium, ameba, bacteria, and many algae

2) budding

A) in unicellular organisms

* similar to binary fission BUT has an unequal division of cytoplasm; offspring is smaller than the parent

B) in multicellular organisms

* a bunch of cells form a smaller organism on the original if conditions are favorable
* the bud develops into a fully functional organism which may or may not detach from the parent

3) sporulation

* spores are single, specialized cells that are released from the parent and can develop into new individuals if the conditions are right
* occurs in molds and mushrooms

4) regeneration

A) of body parts

* new tissues can be produced to replace those lost or damaged
* occurs in such animals as lobsters, crabs, and gecko lizards

B) new organisms

* when an entire new organism is produced from part of the original organism
* occurs in seastars and planarians (a type of simple annelid)

(as long as a ray--one of the points--has some of the center piece, it can grow into a whole new seastar!)

5) vegetative propagation

* when new plants develop from roots, stems or leaves of the parent organism
* many different types

A) cuttings
* a new plant grows from a piece of the parent
* ex. coleus, geraniums

B) bulbs
* bulbs bud from parent plants
* can grow into new individuals
* ex. onions, tulips

C) tubers
* stem-like structures that grow underground from the parent
* can form new individual organisms if the conditions are right
* ex. potatoes

D) runners
* stem-like structures that grow above the soil from the parent
* when it reaches a favorable spot (enough light, water...) it will grow into a new individual
* ex. strawberries, ivy

E) grafting
* special tissues--called cambium (embryonic) tissues can be attached to a cutting of a parent plant
* ex. seedless oranges

* can artificially grow plants with different characteristics that are desirable!

Mitosis and Asexual Reproduction