1. Reproduction by Asexual Means
MITOSIS
Reproduction by Asexual Means
Regents Biology

2. KEY WORDS anaphase asexual reproduction binary fission budding
OBJECTIVES
Upon completion of this unit students will be able to:   
1. Name and describe the two types of reproduction and the two basic processes
involved in cell division.
2. Explain what happens in interphase and in the stages of mitosis.
3. Differentiate interphase and mitosis in plant and animal cells.
4. Discuss how mitosis is controlled.
5. Discuss what cancer is.
6. Describe the types of asexual reproduction and vegetative propagation.
KEY WORDS
anaphase
asexual reproduction
binary fission
budding
cell plate
centromere
chromatid
chromatin
chromosomes
cytokiniesis
interphase
metaphase
mitosis
prophase
regeneration
sexual reproduction
spindle fiber
sporulation
telophase
vegetative propagation

3. OVERVIEW
Cell division is the simplest form of reproduction. This process involves several complex steps that result in the division of one cell into two identical cells. Single-celled organisms are able to produce more individuals like themselves using the process of cell division. Some multi-celled organisms may also utilize this process to reproduce identical offspring or result in the overall growth of the organism. “Asexual” (literally, “without sex”) is the term used to describe this mode of reproduction.
Asexual reproduction involves the production of new organisms of a species from a cell or cells of a single parent organism. There is no fusion of cells or cell nuclei in asexual reproduction. Instead, there is a duplication of the nucleus in the production of more cells with characteristics identical to those of the single parent organism.

4. TYPES OF REPRODUCTION
There are two basic types of reproduction:
1.ASEXUAL: THERE IS ONLY ONE PARENT; NO SPECIAL REPRODUCTIVE CELLS/ORGANS ARE INVOLVED; THE NEW INDIV. IS SEPARATE FROM THE PARENT
2. SEXUAL: INVOLVES THE UNION OF TWO NUCLEI FROM SPECIAL CELLS; THESE ARE USUALLY PRODUCED BY TWO SEPARATE ORGANISMS
Some organisms produce only asexually, others produce only sexually, and still others can reproduce by either method.

5. MITOSIS AND CYTOKINESIS
In our cytology unit we learned that the cell theory states that ALL CELLS ARISE FROM PRE-EXISTING CELLS BY CELL DIVISION. This type of cell division is called MITOTIC CELL DIVISION and involves two distinct stages:

6. 1.MITOSIS: NUCLEAR DIVISION; A DUPLICATION OF THE CONTENTS OF THE PARENT CELL NUCLEUS, FOLLOWED BY AN ORDERLY SEPARATION OF THOSE CONTENTS INTO TWO NEW, IDENTICAL NUCLEI
2. CYTOKINESIS (CYTOPLASMIC DIVISION): THE CYTOPLASM OF THE CELL IS DIVIDED INTO TWO PARTS, EACH CONTAINING ONE OF THE NEWLY FORMED NUCLEI; THE DAUGHTER CELLS SHARE THE SAME # OF CHROMOSOMES AS WELL AS IDENTICAL GENETIC CHARACTERISTICS

7. A. Nuclear Material
The hereditary material of the nucleus is DNA (DEOXYRIBONUCLEIC ACID)
The information necessary for the SYNTHESIS of all components of each cell is stored in THE STRUCTURE OF DNA.
The DNA also includes information that DETERMINES THE MAKEUP AND FUNCTION OF THE ORGANISM and this information must be passed on to all cells produced.
DNA is found in CHROMATIN (LONG, THIN, TWISTING THREADS)

8. During cell division, THE CHROMATIN BECOMES ORGANIZED INTO CHROMOSOMES
Each type of organism has a specific number of CHROMOSOMES in its body cells; HUMANS HAVE 46 CHROMOSOMES
When cells reproduce, the new cells must have the SAME number of chromosomes as the original cell.
The number of chromosomes in the body cells of an organism is CONSTANT; since each chromosome makes up only part of the DNA, each cell must receive an entire set of chromosomes to function properly.

9. Interphase in a plant cell
B. Interphase
Interphase is NOT a phase of mitosis; the phases of mitosis are PROPHASE, METAPHASE, ANAPHASE AND TELOPHASE
When a cell is between mitotic cycles, it is in INTERPHASE and is also known as THE RESTING STAGE
Interphase lasts from THE END OF ONE CELL DIVISION TO THE BEGINNING OF THE NEXT
During interphase, EACH CHROMOSOME
MAKES A COPY FOR ITSELF (REPLICATES)
AND IS ACTUALLY A DOUBLE
CHROMOSOME
DNA appears AS A TANGLED,
THREADLIKE MASS OF CHROMATIN
Near the nucleus are the CENTRIOLES,
which also REPLICATE DURING
INTERPHASE FORMING 2 PAIRS
Interphase in a plant cell

10. During prophase, THE DOUBLE CHROMOSOME BECOMES VISIBLE
C. The Phases of Mitosis
1. Prophase
During prophase, THE DOUBLE CHROMOSOME BECOMES VISIBLE
The two halves of each double chromosome are called CHROMATIDS and are connected at the CENTROMERE

11. Prophase in a plant cell
In early prophase, THE TWO PAIRS OF CENTRIOLES MOVE TOWARDS THE POLES
Fibers extending outward from the centrioles are called ASTERS
PLANT CELLS DO NOT have CENTRIOLES and therefore there is no formation of ASTERS.
Other threadlike fibers extend between the poles: SPINDLE FIBER
In late prophase, the double chromosomes move toward the EQUATOR and THE NUCLEAR MEMBRANE AND NUCLEOLUS DISAPPEAR
Prophase in a plant cell

12. Metaphase in a plant cell
MY FAVORITE PHASE!!!!! 
During metaphase, THE CENTROMERES ARE LINED UP ON THE EQUATOR
In late metaphase, EACH DOUBLE-STRANDED CHROMOSOME GIVES RISE TO TWO SINGLE-STRANDED, IDENTICAL CHROMOSOMES
Metaphase in a plant cell

13. Anaphase in a plant cell
During anaphase, THE DUPLICATE CHROMOSOMES MOVE APART TO OPPOSITE POLES WITH THE AID OF THE SPINDLE FIBERS
Anaphase in a plant cell

14. Telophase in an animal cell
Telophase begins when THE CHROMOSOMES REACH THE POLES
The chromosomes elongate, uncoil, and begin to appear like chromatin (as in pre-interphase)
The spindle and asters disappear
A nuclear membrane forms around each daughter nucleus
The nucleoli reappear
The nuclear division of an animal cell is complete!
Telophase in an animal cell

15. Cytokinesis
Cytokinesis is NOT a phase of mitosis, it is THE DIVISION OF THE CYTOPLASM AFTER MITOSIS
Cytokinesis begins during late ANAPHASE and is completed during TELOPHASE
In ANIMAL CELLS, cytokinesis is accomplished by the “PINCHING” or furrowing of the cell membrane.
This “pinching in” results in THE FORMATION OF TWO DAUGHTER CELLS OF THE SAME SIZE
In PLANT CELLS, the rigid cell wall does not pinch during telophase. Instead, A CELL PLATE FORMS ACROSS THE MIDDLE OF THE CELL

19. ASTERS CENTRIOLES EQUATOR SPINDLE FIBERS CHROMATIN CHROMATIDS
NUCLEAR MEMBRANE
CENTROMERE
CHROMATIDS
NUCLEOLUS
SISTER CHROMATIDS
SPINDLE FIBERS
EQUATOR
POLE
POLE
CLEAVAGE FURROW
DAUGHTER CELLS

20. E. CONTROL OF MITOTIC CELL DIVISION
Exactly how mitosis is started and controlled is unknown to us.
In unicellular organisms, it is thought that AN INCREASE IN SIZE TRIGGERS MITOSIS
Normally, in multicellular organisms, CELL DIVISION OCCURS ONLY AS NEEDED FOR REPAIR AND GROWTH
CANCER: UNCONTROLLED CELL DIVISION

21. In a very short time cancer may produce
Normal mitotic cell division results in the production of new cells for growth and for the repair of damaged or worn-out body tissues. It is a process that is controlled within the cell itself, and that occurs countless times in living things without flaw. However, in some cells at some times, the mitotic process appears to break down and begins to occur so rapidly that insufficient time is available for normal replication and chromosome separation. This rapid, abnormal cell division is known as cancer.
In a very short time cancer may produce
a large number of such abnormal cells,
which begin to crowd out the normal
tissues, resulting in damage to these
tissues and often in the death
of the host organism.
Cancer of the larynx

22. F. TYPES OF ASEXUAL REPRODUCTION
Because asexual reproduction involves only MITOTIC CELL DIVISION, each offspring has the same hereditary information as its parent.
Asexual reproduction results in STABLE CHARACTERISTICS WITHIN A SPECIES FROM ONE GENERATION TO THE NEXT
Asexual reproduction is generally EFFICIENT in that it is generally RAPID and often results in the production of LARGE MEMBERS OF OFFSPRING.

23. · Binary fission is THE SIMPLEST FORM OF ASEXUAL REPRODUCTION
·      The parent organism DIVIDES INTO TWO EQUAL PARTS
·      Each of the daughter cells BECOMES A SEPARATE INDIVIDUAL AND GROWS TO NORMAL SIZE
·      No parent is left by this method because THE PARENT HAS BECOME TWO INDIVIDUALS
·      Organisms that perform binary fission: BACTERIA, PROTOZOA, AMEOBA
BINARY FISSION is accomplished when a single cell undergoes mitosis followed by equal cytoplasmic division, forming two daughter cells having roughly the same size and shape and containing identical genetic information.

24. · Budding is where THE PARENT ORGANISM DIVIDES INTO TWO UNEQUAL PARTS
·      Budding results in DAUGHTER CELLS OF UNEQUAL SIZE, BUT CONTAINING IDENTICAL GENETIC INFORMATION
·      The larger of the two cells may divide rapidly several more times, producing A CHAIN OR COLONY OF DAUGHTER CELLS
·      Organisms that perform budding: YEAST, HYDRA
BUDDING is when new embryonic cells begin to form by mitosis within the mature tissues of the organism. As these embryonic tissues begin to differentiate (specialize) they take on the physical appearance of the parent organism. After a period of growth, the new organism, or “bud”, identical to the parent organism, separates from the parent and begins to live an independent existence.

25. 3. SPORULATION/SPORE FORMATION
Sporulation is the FORMATION OF SPECIALIZED REPRODUCTIVE CELLS CALLED SPORES
Spores can be formed SEXUALLY OR ASEXUALLY and contain A NUCLEUS SURROUNDED BY CYTOPLASM
Asexually formed spores are the products of MITOTIC CELL DIVISION, and are a common method of reproduction in FUNGI (MOLD, MUSHROOM), ALGAE, PROTOZOA
SPORULATION is the formation of specialized reproductive cells, known as spores, within the parent organism. Each spore contains a nucleus surrounded by cytoplasm. When these spores are released from the parent plant and land in an environment containing conditions favorable to their growth, they begin to undergo mitotic cell division. The spores of most species require moisture and warmth to germinate. The mitotic divisions result in the formation of a new multicellular organism genetically identical to the original parent organism.

26.  4. REGENERATION
REGENERATION: THE ABILITY OF AN ORGANISM TO REGROW LOST BODY PARTS
Organisms that reproduce by regeneration include: HYDRA, PLANARIA, STARFISH, EARTHWORM
The capacity for organisms to regenerate decreases as THEY BECOME MORE COMPLEX (I.E., INVERTEBRATES REPRODUCE AND REPAIR DAMAGED TISSUES BY REGENERATION MORE READILY THAN VERTEBRATES)
Although simple organisms have great capacities for regeneration, THEY DO NOT REPRODUCE BY THIS METHOD UNDER NATURAL CIRCUMSTANCES

27. 5. VEGETATIVE REPRODUCTION
Vegetative structures: ROOTS, STEMS, LEAVES and function in NUTRITION AND GROWTH OF PLANTS
When vegetative structures give rise to a new plant, the process is called VEGETATIVE PROPAGATION
In vegetative reproduction, undifferentiated (unspecialized) cells divide mitotically and then become specialized to GIVE RISE TO AN INDEPENDENT PLANT
The new plant has THE SAME HEREDITARY CHARACTERISTICS AS ITS PARENT
Vegetative propagation may occur NATURALLY OR ARTIFICIALLY

28.  1.NATURAL VEGETATIVE PROPAGATION
BULBS: BULBS BUD FROM PARENT BULBS AND IS MADE UP OF EMBRYONIC TISSUES THAT FORM LEAVES AND FLOWERS; UNDERGROUND STEM W/ LEAF STRUCTURE; ONION AND TULIP
TUBERS: UNDERGROUND STEMS FOR STORING EXCESS FOOD; POTATO
RUNNERS: STEMLIKE STRUCTURES THAT GROW FROM THE MAIN STEM OF THE PARENT PLANT OVER THE SURFACE OF THE SOIL; POISON IVY AND STRAWBERRIES

29. 2.ARTIFICIAL VEGETATIVE PROPAGATION
CUTTINGS: REMOVING A PORTION OF THE ROOT, STEM, OR LEAF AND STIMULATING IT TO GROW AND REPLACE THE MISSING PARTS OF ITS BODY AND BECOME AN INDEPENDENT ORGANISM; COLEUS AND GERANIUM PLANTS
GRAFTINGS: EMBRYONIC TISSUES (CAMBIUM) OF ROOT STOCK ARE ATTACHED TO LIKE TISSUES OF AN UPPER STEM TAKEN FROM THE PARENT PLANT TO BE REPRODUCED; COMMERCIAL GROWERS PRODUCE LARGE QUANTITIES OF GENETICALLY IDENTICAL PLANTS FOR SALE; ORANGES AND EMPIRE APPLES

30.  ADVANTAGES:
a) Vegetative propagation ensures THE PRODUCTION OF NEW PLANTS EXACTLY LIKE THE PARENT
b) The development of a plant by vegetative propagation often TAKES LESS TIME THAN DEVELOPMENT FROM SEED
c) Plants bearing SEEDLESS FRUIT can only be grown by vegetative propagation
d) GRAFTING can be used to obtain higher yields of fruits or nuts.