Transcript Introduction to Mitosis Biology 12 S.Dosman

Introduction to
Mitosis
Biology 12
S.Dosman
Fertilization
• The union of male and
female sex cells.
Asexual Reproduction
• The production of
offspring from a single
parent; offspring inherit
the genes of that parent
only.
Sexual Reproduction
• The production of offspring from the union of
two sex cells, one from each different parent.
The genetic makeup of the offspring is
different from that of either parent.
Mitosis
• A type of cell division in
which a daughter cell
receives the same
number of
chromosomes as the
parent cell.
Cytokinesis
• The division of the
cytoplasm.
Interphase
• The time interval
between nuclear
divisions. During this
phase, a cell increases
in mass, roughly
doubles the cytoplasmic
components, and
duplicates its
chromosomes.
Chromatin
• The tangled fibrous
complex of DNA and
protein within a
eukaryotic nucleus.
Centromere
• The structure that holds
chromatids together.
Sister Chromatids
• A chromosome and its
duplicate, attached to
one another by a
centromere. The pair
remains attached until
separated during
mitosis.
Centrioles
• Small protein bodies
that are found in the
cytoplasm of animal
cells.
Spindle Fibres
• Protein structures that
guide chromosomes
during cell division.
Spermatocytes
• Sperm producing sex
cells in males; these
cells can divide
continuously.
Blastula
• An embryonic stage consisting of a ball of cells
produced by cell division following the
fertilization of an egg.
Genetic engineering
• Intentional production of new genetic
material by substituting or altering existing
materials.
Enucleated
• The condition where a
cell does not contain a
nucleus.
Totipotent
• Having the ability to
support the
development of an egg
to an adult.
Biotechnology
• The use of living things
in industrial or
manufacturing
applications.
1. List the stages of mitosis. Briefly describe that occurs in each stage.
To help in your description, sketch the sequence of events that occurs
in an animal cell. Include labels for different structures.
• Prophase—chromosomes condense and become shorter and
thicker; centrioles move to opposite poles of the cell; spindle
fibers attach to the centromeres of the chromosomes; the
nuclear membrane starts to dissolve.
• Metaphase—chromosomes line up at the equatorial plate;
the nuclear membrane completely dissolves.
• Anaphase—centromeres divide and the resulting
chromosomes (formerly chromatids) move to opposite poles of
the cell; an identical set of chromosomes moves to each pole.
• Telophase—chromosomes lengthen again; the spindle fibers
dissolve; nuclear membrane forms around the chromosomes.
2. A cell with 10 chromosomes undergoes mitosis. Indicate how
many chromosomes would be expected in each daughter cell.
• Each of the daughter cells contains ten
chromosomes.
• The daughter cells should each contain the
same total number as that of the parent cell.
3. During interphase, what event must occur for the cell to be
capable of undergoing future divisions?
• The genetic material needs to replicate. The
chromosomes must once again become
double-stranded.
4. Using a dictionary, look up the meaning of the prefixes used in the
stages of mitosis: (pro, meta, ana, telo). Why would they be used in
the naming of the phases of mitosis?
• Some common answers might be the
following:
• “pro” — prior to
• “meta” — occurring later than
• “ana” — upward, backward, again
• “telo” — end
• Each prefix matches the events occurring
during each stage of mitosis.
5. Compare and contrast the structure of the daughter cells
with that of the original parent cell.
• Daughter cells are genetically identical to each
other and to the parent cell.
• However, the daughter cells will be smaller
and have fewer organelles than the parent
cell.
6. Describe the structure and explain the function of the
spindle fibres.
• Spindle fibers are composed of microtubules.
• The function of the spindle fibers is to align
and direct chromosomes during cell division.
7. What is the significance of cytokinesis? Speculate what
would happen if cytokinesis did not occur.
• Cytokinesis produces two distinct and
separate cells. It involves the division of the
cytoplasm and organelles.
• If cytokinesis did not occur, mitosis would
result in a single cell with two nuclei.
8. When a cell has reached its maximum size, what two alternatives
does it have? When does the cell carry out one alternative over the
other?
• When a cell reaches its maximum size, it can
divide or die (death does not necessarily occur
immediately; some cells specialize).
• Cell division permits the survival of the
organism or tissue.
9. What would happen if you ingested a drug that prevented
mitosis? What if it only prevented spindle fibre formation?
• Without mitosis there would be no new cells
produced which means no new growth or
replacement of dead cells.
• No spindle fibers means that chromosomes
would not be separated and there would not
be an even division of the DNA.
• Under both circumstances dead cells could
not be replaced and the organism would die.
10. A cell from a tissue culture has 38 chromosomes. After mitosis
and cytokinesis, one daughter cell has 39 chromosomes and the
other has 37. What might have occurred to cause the abnormal
chromosome numbers?
• Both sister chromatids for one of the
chromosomes moved to the same pole.
• The spindle fibers failed to separate them.
• Each sister chromatid duplicated its genetic
information and became a separate, doublestranded chromosome.
11. Suppose that during mitosis, both sister chromatids moved to
the same pole, resulting in daughter cells with a different number of
chromosomes than the parent cell. How might this abnormality
affect cell structure, cell function, or both?
• Students may have difficulty explaining why cells with
too much genetic information have difficulties. The
reason will become clearer once they have examined
nondisjunction; some of the duplicate information may
be contradictory.
• However, one cell would have too much genetic
information, the other cell too little. Chemical directions
carried in the chromosomes are necessary for the proper
functioning of a cell, and, thus, a cell that had too little
genetic information would likely not survive.
• A cell with too much genetic information would also
experience difficulties