1. BIO 101 – Laboratory August 2009
This only serves as your guide. You still have to read your manuals
EXERCISE V
Cell Growth and Division
2 General Processes of Cell Division:
1. Karyokinesis – organization of DNA strands into chromosomes & separation of chromosomes (nuclear
division)
2. Cytokinesis – division of the cell body (cytoplasm & its organelles)
Cell Cycle
events that occur from the completion of one division until the beginning of the next division constitute the
cell cycle
Interphase Stage – interval between divisions
devoted to growth and metabolism
the time for chromosomal replication
1. G1 (1st Gap) – initiation of new cycle
Cells may become non-dividing or continue through G1
2. S Phase – replication of the DNA of each chromosome; DNA Synthesis
3. G2 (2nd Gap) – volume of cell has doubled, DNA has been replicated, mitosis is initiated
MITOSIS
a form of cell division resulting in the production of two cells, each with the same chromosome & genetic
complement as the parent cell
somatic cell division
occurs on cells during embryonic development, growth, repair of injured tissues & replacement of worn-out
tissues
Specimen used:
Allium cepa root tips (plant cell)
Root tips → region of active cell division (meristematic)
Most cells are in Interphase and Prophase stage
Whitefish blastula (animal cell)
Blastula → embryonic stage in the development of a fertilized egg
MEIOSIS
the process that produces haploid gametes in diploid organisms
the cell undergoes two consecutive divisions – Meiosis I & Meiosis II
four daughter cells result from the divisions, in contrast to the two daughter cells produced from mitotic
division
2 divisions of meiosis are preceded by only one duplication of chromosomes → each of the 4 daughter cells
resulting from meiosis has only half as many chromosomes as the starting cells – a single haploid set of
chromosomes
Specimen used: Grasshopper testis (animal cell)
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2. BIO 101 – Laboratory August 2009
This only serves as your guide. You still have to read your manuals
MITOSIS
Allium cepa – root tips
Interphase
Cell is undergoing respiration and synthesis of DNA, RNA, and protein in
preparation for mitosis
Interphase
Prophase
Chromosomes become distinguishable as long, thin tubules in the nucleus
Nuclear membrane begins to break down
Chromosomes are distributed in the cytoplasm as coiled mass
Each chromosome is composed of 2 separate strands – sister chromatids
which are identical
Sister chromatids are joined together at a region of attachment,
centromere
Prophase Within this region is the kinetochore from which projects the spindle to
the 2 poles of the cell
Metaphase
Double stranded chromatids are arranged near the center of the cell at
right angles to the long axis of the spindle fibers forming the metaphase
plate
Metaphase
Anaphase
Chromatids are pulled by the microtubules to opposite poles of the cell
This stage is recognized by the V-shaped chromosomes in 2 groups at
opposite sides of the cell
Anaphase ends when separated chromatids, now called chromosomes
reached the opposite poles
Anaphase
Telophase
Cell plate starts as a fine line across the center of a cell
When complete, the cell plate divides the original cell into 2 daughter
cells
Nuclei begins to reorganize; chromosomes uncoil & become longer &
thinner, nuclear membrane re-forms, and nucleoli begins to reappear
Karyokinesis is completed at the end of telophase and cytokinesis begins
Telophase
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3. BIO 101 – Laboratory August 2009
This only serves as your guide. You still have to read your manuals
MITOSIS
Whitefish blastula
Interphase
with distinct nucleus bounded by a nuclear membrane
with identifiable nucleolus
presence of centrosome (or cell center) containing the centrioles
Interphase
Prophase – stage of preparation
2 pairs of centioles start to move apart to opposite poles
Microtubules – radiate from each pair of centrioles like spokes on a wheel
forming a configuration called Aster
disappearance of the nuclear membrane
appearance of spindle fibers (microtubules + spindle)
short chromosomes become visibly doubled → each chromosome consists
of 2 sister chromatids
Prophase
Metaphase – stage of separation
chromosomes move & align themselves along the equatorial plane
forming the metaphase plate
Metaphase
Anaphase – stage of migration
pair of chromatids are pulled apart by microtubules of the spindle and
become daughter chromosomes
then they are pulled apart toward opposite poles of the cell
Anaphase
Telophase – stage of nuclear reconstruction & cytosome division
spindle disappears, 2 daughter nuclei are organized
nucleoli appear, nuclear membranes are formed
cleavage furrow; cytokinesis takes place
results into 2 daughter cells with the same genetic material as the parent
cell.
Telophase
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4. BIO 101 – Laboratory August 2009
This only serves as your guide. You still have to read your manuals
MEIOSIS I
The resulting cell at the end of Meiosis I is reduced from the diploid to the haploid condition
1. Prophase I
Homologous chromosomes – each are composed of two chromatids
Substages:
Leptotene – chromosomes are long, thin, optically single threads with little coiling
Zygotene – homologous chromosomes begin to pair (synapsis) and lie adjacent to one another to form
bivalents
Pachytene – exchange of genetic components called crossing over is manifested by “X” arrangements
(chiasmata) of portions of homologous chromosomes; portions of each of the paired chromosomes
separates into 2 sister chromatids (structure at this stage is then called a tetrad).
Diplotene – chromosomes clump on the center of the cell
Diakinesis – chromosomes pairs as well separated through the cell. Nucleolus generally disappears and
nuclear membrane begins to break down
2. Metaphase I
Homologous chromosomes (called tetrads) line up side by side at the metaphase plate
Spindle fibers join the centromeres to the poles
Nuclear membrane is completely gone
3. Anaphase I
Homologous chromosomes in each pair separate from each other and move to opposite poles of the cell
4. Telophase I - Chromosomes are regrouped at the poles as in mitosis.
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5. BIO 101 – Laboratory August 2009
This only serves as your guide. You still have to read your manuals
MEIOSIS II
Equational division resulting to four haploid cells
1. Prophase II
Similar to mitosis, it involves the contraction and coiling of chromosomes
Synapsis and crossing over does not occur anymore but the remnants of the crossing over from prophase I is
carried over.
Chromosomes are already reduced from diploid to haploid
2. Metaphase II
Chromosomes line up at the metaphase plate; spindle fibers join the chromosomes to the opposite poles
3. Anaphase II
Sister kinetochores move separately to the poles pulling with them the chromatids to which they are
attached (sister chromatids move to opposite poles).
4. Telophase II
Interphase nuclei are reconstituted and cell walls are laid down to give 4 cells known as a tetrad.
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