Mitosis Versus Meiosis We have learned that MITOSIS is the
DIVISION of SOMATIC cells (Body cells) Purpose is for organism
GROWTH Retain the same number of chromosomes (2n) through out all
divisions In order to produce GAMETES (sex cells), we must go
through a different process MEIOSIS Sometimes thought of as
REDUCTION division Why? MITOSIS- produces two IDENTICAL daughter
cells, each also identical to the original parent cell
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Homologous Chromosomes We inherit half of our DNA from each
parent The combination of our fathers and mothers genes give us our
own unique set of characteristics Somatic cells contain genetic
material that is half from mom and half from dad (2n) HOMOLOGOUS
chromosomes are two sets of chromosomes that control the same genes
One homolog from mom, one from dad
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Meiosis and Chromosome Number The number of chromosomes in any
given organisms cells is defined by the chromosome number N Diploid
number (2n): cells that contain both sets of homologous chromosomes
Aka: ALL somatic body cells Haploid number (n): cells that contain
1 set of inherited DNA AKA: ALL Sex cells (gametes)
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Karyotype: display of chromosomes This is a HUMAN karyotype.
There are 23 pairs of DNA Each pair consists of one version from
mom, and one version from dad (total=46 chromosomes)
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Meiosis Sex Chromosomes the 23rd chromosome, determines gender
Two Forms: X Females have XX Y Males have XY
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Meiosis- reduction of chromosome number MEIOSIS is the
formation of gametes by reducing a diploid cell (2n) into FOUR
genetically different haploid cells (n) *Remember- mitosis divided
one cell into 2 identical cells this this is quite different In
males: formation of haploid sperm cells In females: formation of
haploid egg cells
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Meiosis- 2 sets of division Meiosis I: separation of homologous
chromosomes Each homolog contains an attached copy (sister
chromatids) Meiosis II: separation of sister chromatids This stage
looks identical to Mitosis
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Meiosis I Prophase I Protein cause homologous chromosomes to
stick together along with their length Tetrads the paired
chromosomes Now 4 chromatids Chromosome #: 2n 1 set from mom 1 set
from dad 1(mom)+1(dad)= 2n
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Meiosis I Prophase I Crossing Over 2 nd new step; tetrads
exchange genetic material This process introduces unique, new
traits. This is one way, other than mutations, organisms can
acquire NEW traits
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Meiosis I Metaphase I Tetrads move to the middle of the cell
and line up across the spindle. Notice now chromosomes line up NEXT
to their homologous pair (2 lanes)
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Meiosis I Anaphase I Homologous chromosomes separate and
migrate to opposite poles Sister chromatids migrate together Each
chromosome is made up of two copies
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Meiosis I Telophase I The chromosomes arrive at poles Each pole
has a haploid daughter nucleus because it only has one set of
chromosomes
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Meiosis I Cytokinesis Form two daughter cells Chromosomes in
each daughter cell are still duplicated (double in number)
Chromosome #: n Because moms set and dads set were separated, now
you have haploid number
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Meiosis II Prophase II In each haploid daughter cell, spindle
forms Nuclear envelope disappears
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Meiosis II Metaphase II Chromosomes line-up in the middle of
cell Spindle attaches to centromeres
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Meiosis II Anaphase II Sister chromatids separate and move to
opposite poles
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Meiosis II Telophase II & Cytokinesis Chromatids arrive at
poles Now individual chromosomes Nuclear envelope reforms
Cytokinesis splits cells
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Meiosis Finished Produced four DIFFERENT haploid daughter
cells
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Genetic Variation How chromosomes line- up and separate at is a
matter of chance So the chromosomes that end up in the resulting
cells occur randomly Four combinations possible
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Closure- Did you get it?? 1.What are two sets of chromosomes
that control the same genes called? Homologous chromosomes 2.What
are homologous chromosomes doing when they are crossing over?
Exchanging genetic material 3.What is the chromosome number at the
beginning of meiosis I? at the END of meiosis I? At the end of
Meiosis II? 2n (diploid), n (haploid), n (haploid)
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Bellringer- Name that phase Name each phase that is either
being described or the picture depicts Ready??
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Metaphase I
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Prophase I Homologous chromosomes exchange genetic material by
crossing over and tetrads form
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Anaphase II What is separating here??? Sister Chromatids
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Telophase I Two nuclei form, each containing a haploid set of
replicated chromosomes
Slide 27
Anaphase I Homologous pairs separate and migrate to opposite
ends of the cell
Mitosis vs Meiosis: Cell division processes Mitosis Occurs in
all growing tissue of organisms Purpose is for organism GROWTH
Division of BODY cells (Somatic cells) Examples: hair, blood,
muscle, skin, etc. Meiosis Occurs in the Reproductive Organs of
organisms Purpose is to create GAMETES (sex cells) for sexual
reproduction Examples: Egg cells Sperm cells
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Prophase vs Prophase I MeiosisMitosis Spindle forms Nuclear
membrane breaks down Chromosomes condense Chromosome #: 2n
(diploid) Spindle forms Nuclear membrane breaks down Homologous
chromosomes cross over and form tetrads Chromosome #: 2n
(diploid)
Slide 31
Metaphase vs Metaphase I MitosisMeiosis Chromosomes line up
single file Spindle attaches to centromeres Chromosome #: 2n
(diploid) Homologous pairs line up side- by-side Spindle attach to
centromeres Chromosome #: 2n (diploid)
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Anaphase vs. Anaphase I MitosisMeiosis Sister Chromatids are
pulled apart Cell elongates Chromosome #: 2n (diploid) Homologous
pairs are pulled apart Cell elongates Chromosome #: 2n
(diploid)
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Telophase vs Telophase I (And Cytokinesis) MitosisMeiosis
Cytoplasm divides Nucleus forms Two genetically IDENTICAL daughter
cells form Chromosome #: 2n (diploid) Cytoplasm divides Nucleus
forms 2 different daughter cells form Nuclei is still REPLICATED
Chromosome #: n (haploid)
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Meiosis II MitosisMeiosis
Slide 35
Nuclear Envelope breaks down Spindle Forms
Slide 36
Sister chromatids Line up single file Spindle attaches to
centromeres
Slide 37
Sister Chromatids Separate Cell Elongates
Slide 38
Nuclear Membrane reforms Spindle disappears Cytoplasm begins to
divide via cytokinesis
Slide 39
Cytokinesis divides both cells Now, 4 genetically different
daughter cells All reduced to haploid (n # of chromosomes) Notice
how none are the same
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We Do Activity Visualizing meiosis Take out a piece of paper
and number it 1-8 Take out 3 sheets of blank paper Using scrap
paper, cut 8 small strips of paper Color 4 strips one color Color 4
another color Follow Ms. Hamadehs directions With your table
partner, take out 2 different colored highlighters
Slide 41
Human chromosomes There are 46 chromosomes (23 homologous
pairs) in each somatic cell 22 pairs of autosomes 1 pair of sex
chromosomes XX = Female, XY = Male Karyotype - chromosomes are
arranged according to shape and size
Slide 42
Nondisjunction and chromosomal disorders Nondisjunction failure
of chromosomes to separate and segregate into daughter cells
Nondisjunction may occur during meiosis 1 or meiosis 2 Abnormal
number of chromosomes may result
Slide 43
Normal monosomic gametes Normal meiosis MEIOSIS I MEIOSIS II
Results of crossing- over not shown Replicate DNA
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MEIOSIS I MEIOSIS II Replicate DNA Nondisjunction during
meiosis I Non-disjunction Disomic gametesNullisomic gametes
Slide 45
MEIOSIS I MEIOSIS II Replicate DNA Nondisjunction during
meiosis II Non-disjunction DisomicNullisomicMonosomic gametes
Slide 46
EXAMPLES OF NON-DISJUNCTION
Slide 47
Slide 48
Klinefelter's syndrome, 47, XXY It is the most common sex
chromosome disorder and the second most common condition caused by
the presence of extra chromosomes Symptoms: -Language impairment
-Lanky, youthful build or rounded body type -Low levels of
Testosterone and small testicles / Infertile
Slide 49
Turners Syndrome (X) Common symptoms: Short stature swelling of
the hands and feet Broad chest and widely spaced nipples Low
hairline Low-set ears Reproductive sterility Increased weight,
obesity Small fingernails Characteristic facial features Webbed
neck
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What genetic disorder is this? They may have never known
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Down Syndrome 47, XY, +21
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1 in 1,250 births 47 chromosomes XY or XX #21 Trisomy
Nondisjunction Down Syndrome