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Meiosis/Mitosis
Mitosis, which we just studied is asexual
reproduction. There is no recombination of
genetic material.M
ost higher orderorganism reproduce sexually meaning
there is a recombination of genetics for
every new organism the genetics of
Mom and from dad. So meiosis makesa new ME MEiosis!
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Meiosis
If the sperm and egg cellshad the same number ofchromosomes as theother body cells (2n=46)
a new baby would end upwith 92 chromosomes!!!So obviously sperm andeggs only have thenumber of chromosomes
of other body cells. Theprocess by which they the genetic material iscalled meiosis!
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How it works!
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Section 10.1 Meiosis
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Meiosis Sexual reproduction Formation of new individual
by a combination of twohaploid sex cells (gametes).
Fertilization- combination of
genetic information from twoseparate cells that have onehalf the original geneticinformation
Gametes for fertilization
come from separate parents Female- produces an egg
Male produces sperm
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Meiosis
Both gametes arehaploid, with a single setof chromosomes
The new individual is
called a zygote, with twosets of chromosomes(diploid).
Meiosis is a process toconvert a haploid cell to adiploid gamete, and
cause a change in thegenetic information toincrease diversity in theoffspring.
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Putting It All Together - Fertilization
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Meiosis
Summary of chromosome characteristics
Diploid set for humans; 2n = 46
Autosomes; homologous chromosomes, onefrom each parent (humans = 22 sets of 2)
Sex chromosomes (humans have 1 set of 2)
Female-sex chromosomes are homologous (XX)
Male-sex chromosomes are non-homologous (XY)
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Meiosis
Haploid (n)-- one set
chromosomes
Diploid (2n)-- two sets
chromosomes
Most plant and animal
adults are diploid (2n)
E
ggs and sperm arehaploid (n)
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Meiosis I
Before going into
PROPHASE 1 the
chromosomes
double
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Meiosis I
synapsis and crossing over
also occurs in prophase 1-
this increases genetic
diversity
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Meiosis I
In Metaphase 1
thechromosomes
line upon the
equator
equator
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Meiosis I
In Anaphase 1
thechromosomes
separate and
move toopposite ends
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Mei sis I
In Telophase
2 nuclei are f rmed
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Mei sis II
In prophase II the
nuclearenvel pe is
again diss lved and
the spindle is set upagain. Pr phase II is
identical t pr phase
f mit sis except that
there is half theam unt f
chr m s mes.
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Meiosis II
In metaphase II the
chromosomes line up
randomly at the
equator
Equator
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Meiosis II
In Anaphase II the
centomeres split-siste
chromatids move to
opposite poles
Equator
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Meiosis II
In Telophase II 4
nuclei form around th
chromosomes cells
divide
4 cells have formed
each cell has aH
APLOIDnumber of chromosomes
Watch it again with real
chromosomes
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Importance ofMeiosis
The importance of meiosis in promoting genetic variation
Each daughter cell (gamete) receives
only one distinct chromosome of a homologous pair.
The different pairs of homologous chromosomes
separate independently of each other (during anaphase)
so that the daughter cells have different combinations ofchromosomes.
Crossing over of chromatids between homologouschromosomes
results in an exchange of chromosomal segments
and therefore reshuffling of genes.
Click here for a good review of this section with a goodintroduction to the next section (weird ending but good video)
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Interesting Fact
All of the people alive
today can trace their
ancestors back to about
10,000 people who lived
175,000 years ago. This
is why we share about
99.5% of our DNA with
most everyone on the
planet. So in a way, weare all related.http://www.thetechi.org/genetics
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1.
Through reduction division each gamete
contains the number of chromosomes
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2.
Metaphase 1 homologous pairs line up
Metaphase of mitosis Individual
chromosomes of the 2 sister chromatidsline up
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3.
synapsis The alignment
of chromosomes during
meiosis I (in prophase) so
that each chromosome is
beside its homologue
homologues (A pair of
chromosomes in which
one member of the pair is
obtained from theorganism's maternal
parent and the other from
the paternal parent).
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4.
