Introduction to Mitosis

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Introduction to Mitosis

• Biology 12
• S.Dosman

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Fertilization

• The union of male and female sex cells.

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Asexual Reproduction

• The production of offspring from a single parent
  offspring inherit the genes of that parent only.

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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.

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Mitosis

• A type of cell division in which a daughter cell
  receives the same number of chromosomes as the
  parent cell.

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Cytokinesis

• The division of the cytoplasm.

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Interphase

• The time interval between nuclear divisions.
  During this phase, a cell increases in mass,
  roughly doubles the cytoplasmic components, and
  duplicates its chromosomes.

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Chromatin

• The tangled fibrous complex of DNA and protein
  within a eukaryotic nucleus.

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Centromere

• The structure that holds chromatids together.

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Sister Chromatids

• A chromosome and its duplicate, attached to one
  another by a centromere. The pair remains
  attached until separated during mitosis.

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Centrioles

• Small protein bodies that are found in the
  cytoplasm of animal cells.

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Spindle Fibres

• Protein structures that guide chromosomes during
  cell division.

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Spermatocytes

• Sperm producing sex cells in males these cells
  can divide continuously.

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Blastula

• An embryonic stage consisting of a ball of cells
  produced by cell division following the
  fertilization of an egg.

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Genetic engineering

• Intentional production of new genetic material by
  substituting or altering existing materials.

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Enucleated

• The condition where a cell does not contain a
  nucleus.

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Totipotent

• Having the ability to support the development of
  an egg to an adult.

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Biotechnology

• The use of living things in industrial or
  manufacturing applications.

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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.

• Prophasechromosomes 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.
• Metaphasechromosomes line up at the equatorial
  plate the nuclear membrane completely dissolves.
• Anaphasecentromeres divide and the resulting
  chromosomes (formerly chromatids) move to
  opposite poles of the cell an identical set of
  chromosomes moves to each pole.
• Telophasechromosomes lengthen again the
  spindle fibers dissolve nuclear membrane forms
  around the chromosomes.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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,
  double-stranded chromosome.

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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

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