Sexual Reproduction
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Cellular Reproduction
There are 2 types of reproduction:
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Asexual Reproduction
■
Sexual Reproduction
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Cellular Reproduction
Asexual Reproduction (5 phases)
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1 mother cell divides into 2 daughter cells
Daughter cell is identical to its mother
Interphase + Mitosis
All human cells have 46 chromosomes
called “DIPLOID cells”
Produce SOMATIC cells (not sexual cells)
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Cellular Reproduction
Sexual Reproduction (9 phases)
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1 mother cell divides into 4 daughter cells
Daughter cells have ½ the chromosomes
of their mother (23) “HAPLOID cells ”
Interphase + Meiosis I + Meiosis II
Crossing over of genetic material often
occurs.
SEXUAL cells (egg and sperm) known as
“gametes”
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Vocabulary
Gametes
~ Another name for eggs and sperm
~ They are haploid (In humans, that is 23
chromosomes)
~ They are sexual cells
~ They are produced by sexual reproduction
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Vocabulary
Sperm
+
egg
=
zygote
7
Homologous Chromosomes
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A pair of chromosomes (maternal and paternal)
that have similar/identical shapes and sizes.
Have genes for the same characteristics
(ie: eye color).
Each locus (gene position) controls the same
trait and is in the same place on homologous
chromosomes.
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Vocabulary
Homologous Chromosomes
chromatids
tetrad
chromatids
9
Homologous Chromosomes
Locus
Eye color
Eye color
Hair color
Hair color
Paternal
Maternal
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Sexual Reproduction
■
There are 3 major steps:
~ Interphase
~ Meiosis I
~ Meiosis II
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Meiosis I (4 phases)
~ Prophase I
~ Metaphase I
~ Anaphase I
~ Telophase I
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Crossing Over
■
■
During Prophase I
One chromatid of each
chromosome crosses
over with the chromatid
of the other
chromosome.
■ The result is an
exchange of their
genetic material
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15
Meiosis II (4 phases)
~ Prophase II
~ Metaphase II
~ Anaphase II
~ Telophase II
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Meiosis II
Interphase II – does not exist
** Don’t forget!! This process is
now occurring in both daughter
cells created during Meiosis I
**
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Attention!!!!!!!!!!!!!
■
Female meiosis is somewhat
different. 4 gametes are
initially created, but Cytokenisis
is UNEQUAL. In this case, ONE
GAMETE survives, and the
other 3 are not viable.
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Extra Notes
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Interphase
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Same as Interphase in Mitosis
Chromosome replication, growth and
preparation (chromatin rolls etc)
Each of the replicated chromosomes
possesses 2 chromatids which are
attached at their centromere.
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Prophase I
■
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2 homologous chromosomes combine. This
combination is called a TETRAD
Spindle fibers grow, and attach to each
side of the tetrad
The nuclear membrane and the nucleolus
both disappear
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Metaphase I
■
Spindle fibers pull on the
tetrads, and align them in the
centre of the cell.
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Anaphase I
■
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The tetrads separate and
homologous chromosomes travel
to the poles.
Homologous chromosomes are
still attached by their
centromeres.
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Telophase I/Cytokinesis
■
Each pole has a diploid number of
chromosomes.
■
Cytokinesis - 2 diploids cells are formed.
■
Spindle fibers and centrioles disappear.
■
The nuclear membrane sometimes reforms, and
the nucleolus does not reform at this point.
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Prophase II
■
Same as Prophase in Mitosis
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Metaphase II
■
Same as Metaphase in Mitosis
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Anaphase II
■
■
Same as Anaphase in Mitosis
DON’T FORGET! Chromosomes are
separated into chromatids.
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Telophase II/Cytokenisis
■
Same as Telophase in Mitosis
EXCEPT with a haploid number of
chromosomes
■
The nucleolus and nuclear membrane reform
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Cytokinesis
Important: 4 haploid gametes are formed.
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Telophase II/Cytokinesis
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