Mitosis – Cell Division
A cell is a living thing and thus has a life cycle. A cell life called the cell cycle. A cell life cycle begins with the formation of a
new cell and is completed when the cell has divided to form 2 new daughter cells. Each new cell then begins the cycle again.
The main stages of the cell cycle are interphase (G1, S, G2), mitosis and cytokinesis.
Mitosis: is the reproduction of the nucleus in the parent cell and cytokinesis is the division of the cytoplasm and its organelles.
Instructions: Draw diagrams of the following stages, consult the suggested web pages, textbooks or follow the instructions of
your teacher.
Interphase:
A cell spends most of its life in a stage called interphase. During the Gap 1 (G1)
phase the cell grows, RNA is synthesized and organelles are duplicated. During
the Synthesis (S) phase, the DNA content of the cell doubles and the genetic
information of the cell is copied (DNA replication). This ensures that a complete
set of genes is available to both of the 2 new cells formed during cell division.
During Gap 2 (G2) phase, the cell still synthesizes proteins, RNA and other
molecules, but now it contains twice as much DNA in its nucleus. Cell growth
continues and when the cell is large enough, the cell synthesizes a substance,
which triggers cell division (MITOSIS AND CYTOKINESIS).
Prophase:
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Double stranded chromosomes condense and become visible
nuclear envelope disappears
spindles form
spindle fibres begin to attach to the chromosomes at centromere
 (spindle microtubules are used to separate chromosomes)
Metaphase:
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Double stranded chromosomes line up along the mid-line of the cell.
Spindle is completely formed
Line up perpendicular to spindle apparatus
Chromosomes move to the centre of the cell
Anaphase:
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Chromosome strands are pulled towards the poles by the spindle apparatus
they split at centromere.
Become single stranded chromosomes
Telophase:
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Chromosomes gather at poles
Nuclear envelopes forms around the chromosomes
End of Mitosis
Beginning of Cytokinesis (Division of the cytoplasm)
 (cell plate formation in plants)
An Introduction to Meiosis
In order for life forms to continue their species, they must be able to reproduce. This may be done sexually or
asexually.
 Sexual Reproduction: requires male and female individuals, which each have different and unique sex cells.
When these cells are united, a new individual is formed. The sex cells are called gametes. Gametes, like all
other cells, have chromosomes in their nuclei. When gametes combine, the genetic information in the 2 gametes
also combines. Because they are formed from two different individuals, sexual reproduction increases genetic
variation.
 Asexual reproduction: new individuals originate from a single parent. The parent may divide into 2 or more
individuals or new individuals arise as buds from the body of the parent. (BSCS: page 137; Nelson : page 539)
Gametes:
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males produce sperm cells
females produce egg cells (ovum)
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The cells of an organism have a fixed number of chromosomes. For example, white corn plants have only 20
chromosomes.
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Humans have 46 (double stranded) chromosomes. Human gametes then have only 23 chromosomes. An
individual receives 23 from each parent for a total of 46.
 So gametes have “n” number of chromosomes and are called haploid (n)
 the zygote (sperm + egg) have 2n number of chromosomes and are called diploid (2n).
Gamete (Sex cells) = n = haploid (refers to one half of the full complement of chromosomes). Sex cells have
haploid chromosomes numbers.
Zygote = 2n = diploid (refers to the full complement of chromosomes). Every cell of the body, with exception of
the sex cells, contains the diploid chromosome number.
Meiosis
Terms:
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Homologous Chromosomes: are similar in size, shape and gene arrangement.
Meiosis I (the Reductive division - because the chromosome # is reduced by half.)
(Sketch in the appropriate diagram for each.)
Prophase I
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nuclear membrane disappears
chromosomes condense (become visible)
line up in HOMOLOGOUS PAIRS
called tetrads (because each is made of 4 chromatids)
Crossover may occur (parts of one chromatid may be exchanged for parts of
another) – the exchange of genetic material between two homologous
chromosomes
-Please be sure to include the crossover diagram in your notes. (see space provided)
Spindle fibres have formed
Metaphase I
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chromosomes line up in pairs along the equatorial plate (centre)
spindle fibres help to guide them into place
Anaphase I
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homologous chromosomes move toward opposite poles (segregation)
(i.e. one whole chromosome is sent to each side)
**reductive division occurs here because one member of each homologous pair
will be found in the new cells.
The diploid mother cell becomes two haploid daughter cells
Chromosomes are still double stranded (consist of two sister chromatids)
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Telophase I
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2 cells
MEIOSIS II (happens in each of the daughter cells)
Prophase II
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nuclear membrane disappears
spindle fibres form
NO Additional Crossover
Metaphase II
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Arrange themselves along equatorial plate
(chromatids are still attached (double stranded))
Anaphase II
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Chromsome divides into two chromatids which move to the poles (pulled by
spindle)
Chromosomes are now single stranded.
Telophase II
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Nuclear membrane begins to reform
Cytoplasm divides (cytokinesis)
4 cells with “n” number of
chromosomes.
Four daughter cells are produced as a result of each meiotic division.
nuclear membrane begins to form in the two new cells
cytokinesis occurs = two new cells
Cells do not have identical information
You now have 2 cells with a haploid amount of genetic information
Extra Info:
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Gametogenesis: the formation of sex cells during meiosis.
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Human Gametogenesis: There are two types
a) Spermatogenesis produces four sperm cells (designed for movement and have less cytoplasm)
b) Oogenesis produces one ootid (unfertilized egg cell) – non motile and has more cytoplasm to contain the
nutrients and organelles needed in the event of fertilization.
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Sex chromosomes: the last pair of chromosomes (males = XY; females XX)
Autosomes: chromosomes that are not sex chromosomes
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Be sure to include a diagram of Human Gametogenesis at this point.
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