Meiosis
Sexual Reproduction
Reproduction
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Reproduction: the process by
which an organism produces others
of its same kind.
Two types of reproduction
1. Asexual
2. Sexual-requires two organisms
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Sexual reproduction usually requires
two organisms.
Asexual Reproduction
Two Types;
1. Fission
2. Budding
Regeneration
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Asexual Reproduction
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In asexual
reproduction, a new
organism is produced
from one organism.
The new organism will
have hereditary
material identical to
the hereditary material
of the parent
organism.
Organisms with
eukaryotic cells
asexually reproduce by
cell division.
Asexual
Reproduction:Fission
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Fission occurs when an
organism copies its
genetic material and
then divides into two
identical organisms.
Bacteria do not have a
nucleus, so they can’t
use mitosis.
Bacteria reproduce
asexually by fission.
Asexual Reproduction
Budding
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Budding is a type of
asexual
reproduction made
possible because of
cell division.
When the bud on
the adult becomes
large enough, it
breaks away to live
on its own.
Regeneration
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Some organisms can
re-grow damaged or
lost body parts.
Regeneration: the
process that uses cell
division to regrow body
parts.
Sponges, planaria, sea
stars, and some other
organisms can use
regeneration for
asexual reproduction.
Newt Limb
regeneration
Sexual Reproduction
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sexual reproduction:
Two sex cells,
sometimes called an
egg and a sperm,
come together.
Sex cells are formed
from cells in
reproductive organs.
Sperm are formed in
the male reproductive
organs.
Eggs are formed in the
female reproductive
organs.
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The joining of an egg
and a sperm is called
fertilization, and the
cell that forms is called
a zygote (ZI goht).
Following fertilization,
cell division begins. A
new organism with a
unique identity
develops.
Diploid and Haploid Cells
The human body forms two
types of cells:
1.
Diploid
2.
Haploid
Diploid Cells- Body Cells such
as brain, skin, bones, and
other tissues and organs
are formed from body
cells.
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Human body cells have
23 pairs of chromosomes
or 46 chromosomes.
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When cells have pairs of
similar chromosomes,
they are said to be
diploid.
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Haploid Cells- Sex cells
such as sperm and eggs.
Haploid cells have only half
the number of chromosomes
as body cells
Human sex cells have only
23 chromosomes— one
from each of the 23 pairs of
similar chromosomes.
Because sex cells do not have
pairs of chromosomes, they
are said to be haploid.
Meiosis and Sex Cells
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A process called meiosis (mi OH sus) produces
haploid sex cells.
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Meiosis ensures that the offspring will have the same
diploid number as its parent.
After two haploid sex cells combine, a diploid zygote is
produced that develops into a new diploid organism.
During Meoisis, two divisions of the
nucleus occur: Meiosis I and
Meiosis II
Meiosis I
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each chromosome
is duplicated, just
as in mitosis.
is visible under the
microscope as two
chromatids.
Prophase I
Each duplicated
chromosome comes near its
similar duplicated mate.
Now called homologous
pairs.
-Half chromosomes from one
parent, half from the other.
-Each chromosome contains
genes that code for the
same inherited traits: eye
color, hair color
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Metaphase I
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The homologous
pairs line up in the
center of the cell.
The centromere of
each chromatid pair
attaches to one
spindle fiber.
Anaphase I
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Homologous pairs
of chromosomes
separate and move
to opposite ends of
the cell.
Each duplicated
chromosome still
has two
chromatids.
Telophase I
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The cytoplasm
divides, and two
new cells form.
Each new cell has
one duplicated
chromosome from
each similar pair.
Meiosis II
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The two cells formed during meiosis I, now
begin meiosis II.
Propase II
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Chromosomes
recondense.
A new spindle
forms.
Metaphase II
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Chromosomes
move to the center
of the cell.
Unlike what occurs
in metaphase I,
each centromere
now attaches to
two spindle fibers
instead of one.
Anaphase II
• the chromatids
separate and move
to opposite ends of
the cell.
• Each chromatid
now is an individual
chromosome.
Telephase II
• the spindle fibers
disappear
• a nuclear membrane
forms around the
chromosomes at each
end of the cell.
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When meiosis II is
finished, the cytoplasm
divides.