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11-4 Meiosis
Understand that homologous chromosomes separate randomly during meiosis to produce haploid gametes.
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MT: Sexual Reproduction
11-4 Meiosis
CELL DIVISION:
MEIOSIS & SEXUAL
REPRODUCTION
Images: Peter, Lois & Stewie, The Family Guy From the Virtual Cell Biology Classroom on ScienceProfOnline.com
11-4 Meiosis
WHAT IS HAPPENING HERE?
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11-4 Meiosis
FERTILIZATION
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= when a male and female gamete join
11-4 Meiosis
CHROMOSOME # Most organisms are diploid and thus want an offspring
that is also diploid
So, each gamete has to be haploid so when they join they create a diploid organism
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mitosis
mitosis
meiosis
meiosis
11-4 Meiosis
FIND CHROMOSOME #
DIPLOID #
Human 46 chromosomes Dog 78 chromosomes Carrot 18 chromosomes Goldfish 94 chromosomes Wheat 42 chromosomes Tobacco 48 chromosomes
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HAPLOID #
Human __ chromosomes Dog __ chromosomes Carrot __ chromosomes Goldfish __ chromosomes Wheat __ chromosomes Tobacco __ chromosomes
2339
947
2124
11-4 Meiosis
haploid (n) + haploid (n) = diploid (2n)
OR
Female gamete + male gamete = offspring somatic cell
OR
½ + ½ = 1
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11-4 Meiosis
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CHROMOSOME NUMBER
These two sets of chromosomes are homologous.
One chromosome from mom and one chromosome from dad.
11-4 Meiosis
HOMOLOGOUS CHROMOSOMES
• PairPair of chromosomes that contain the same alleles for a trait
• EX: chromosome with eye color allele from mom is homologous to chromosome with eye color allele from dad
Mom Mom (1,3)(1,3)
Dad Dad (2,4)(2,4)
11-4 Meiosis
WHICH PAIR UP TO MAKE HOMOLOGOUS CHROMOSOMES?
How many pairs of homologous chromosomes are shown?
How many chromosomes are shown?
Pink with pink; yellow with yellow; blue with blue
3
6
11-4 MeiosisWhat happens during the process of
meiosis?
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making of non-identical making of non-identical haploid gameteshaploid gametes
11-4 Meiosis
PHASES OF MEIOSIS I
Meiosis I
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Prophase I Metaphase I Anaphase I Telophase I and
Cytokinesis
Interphase I
11-4 Meiosis
INTERPHASE 1
DNA copies itself
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nucleusnucleus
centriolescentrioles
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PROPHASE INuclear membrane disappears.
Homologous chromosomes pair up to form a tetrad.Tetrad = 4 sister chromatids
Crossing over occurs
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11-4 Meiosis
CROSSING OVERWhen homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over.
Crossing-over produces new combinations of alleles.
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Does crossing over always occur at the Does crossing over always occur at the same allele?same allele?
NO! It is NO! It is randomrandom
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METAPHASE 1
Homologous chromosomes line up in middle of cellSpindle fibers attach to the chromosomes’ centromeres.
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11-4 Meiosis
ANAPHASE 1
The fibers pull the homologous chromosomes toward opposite ends of the cell.
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11-4 Meiosis
TELOPHASE 1
The cell separates into two cells
Nuclear membranes reappear
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11-4 Meiosis
PHASES OF MEIOSIS II
Meiosis II
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Telophase II and
Cytokinesis
Prophase II Metaphase II Anaphase IITelophase I and Cytokinesis I
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NOPE!
Cells DO NOT need to grow or copy DNA since they are trying to get smaller
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11-4 Meiosis
PROPHASE II
Nuclear membrane disappears.
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11-4 Meiosis
METAPHASE II
Individual chromosomes line up in the middle of cell.
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11-4 Meiosis
ANAPHASE II
The sister chromatids separate and move toward opposite ends of the cell.
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11-4 Meiosis
TELOPHASE II
Meiosis II results in four non-identical haploid cells.
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11-4 Meiosis
GAMETE FORMATIONIn male animals, meiosis results in four equal-sized gametes called sperm.
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11-4 Meiosis
GAMETE FORMATIONIn many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction.
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11-4 Meiosis
Image: Meiosis diagram, Marek KultysFrom the Virtual Cell Biology Classroom on ScienceProfOnline.com
View Meiosis Animation
11-4 Meiosis
Image: Mitosis diagram & Meiosis diagram, Marek Kultys From the Virtual Cell Biology Classroom on ScienceProfOnline.com
11-4 Meiosis
MITOSIS VS. MEIOSIS
2n
Clone
Same genetic information in parent cell and daughter cell.
Give me another one just like the other one
VIDEO
1n
Daughter cells different from parent cell and from each other.
Daughter cells have ½ the number of chromosomes as somatic cell.
Shuffling the genes(Mix it up!)
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
11-4 Meiosis
WEBSITES TO CHECK OUT
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1. http://www.cellsalive.com/meiosis.htm
2. http://www.pbs.org/wgbh/nova/baby/divi_flash.html
3. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html
4. http://www.youtube.com/watch?v=uh7c8YbYGqo
