chapter 8 cellular reproduction: cells from cells
TRANSCRIPT
CHAPTER 8CHAPTER 8
Cellular Reproduction:Cells from Cells
You began life as a single cell, but there are now more cells in
your body than stars in the milky way.
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THE BIG PICTURE:
BIOLOGY IS THE STUDY OF LIFE
ALL life is made of cells.
Cells divide and reproduce by using the information of DNA.
Figure 8.1
This was YOUR “baby” picture
You couldn’t do much
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AND LOOK AT YOU NOW !
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In this chapter, we will discuss how
cells divide, a topic that has fascinated
scientists since they first observed
it through a microscope more
than 100 years ago.
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and just like carefully
watching a game played repeatedly,
they have been able to figure out the rules
of cell division
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ALL LIFE IS MADE OF CELLS
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There are WELL over 50 TRILLION CELLS IN A HUMAN BODY
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Perspective on 50 trillion
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Perspective on 50 trillion
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Perspective on 50 trillion
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And all those cells divided from just 1 fertilized egg cell
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There are two kinds of cell division:
1.Mitosis - making a “photocopy” of a cell
• (for growth and maintenance)
2.Meiosis – taking a cell & “halving” it
• (for sexual reproduction)
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MITOSIS
MEIOSIS-testicles-ovaries
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MITOSIS
PARENT CELL
“DAUGHTER” CELL
“DAUGHTER” CELL
START > > > > > END
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SP
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MEIOSIS – IN MALES
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MEIOSIS – IN FEMALES
START > > > > > END
EG
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MITOSIS HAPPENS IN YOUR TOES, TOO
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Mitosis:- Happens everywhere BUT sex cells (testicles
or ovaries)
- Produces 2 genetically identical "daughter" cells from a single "parent" cell.
- Grew you from a single fertilized cell to the person you are today.
- Repairs / Replaces cells lost through everyday wear and tear- ex: skin cells
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MeiosisMeiosis, on the other hand, is quite different.
It shuffles the genetic deck, generating “daughter” cells that are distinct from one another and from the original parent cell.
only a few special cells (sex cells) are capable of meiosis:
- Female > eggs - males > sperm
So, basically, mitosis is for growth and maintenance, while meiosis is for sexual reproduction.
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A QUICK CHECK
What is the cellular process that produces identical “daughter” cells? ___________________
What is the cellular process that takes place everywhere in your body but your sex cells? __________________
What is the cellular process that made you grow from a single cell to the person you are today?
______________
What is the cellular process that only produces sex cells? ______________________
Who lives in a pineapple under the sea? ___________
MITOSIS
MITOSIS
MITOSIS
MEIOSIS
S.B.S.P.
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THE CELL CYCLE
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THE CELL CYCLE
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Phases of CELL DIVISIONINTERPHASE
PROPHASE
PROMETAPHASE
METAPHASE
ANAPHASE
TELEPHASE CYTOKINESIS
1 C
ELL
->->
->2
CELLS
MITOSIS
NOT MITOSIS
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Phases of CELL DIVISION
INTERPHASE – cell grows to make room (G1), makes a copy of each chromosome(S), but the old copies of the chromosomes are stuck to the copied ones (G1, S, & G2)
PROPHASE - In the nucleus, copied chromosomes condense and become visible. Outside the nucleus in the cytoplasm, the spindles forms.
PROMETAPHASE – Nuclear membrane breaks up, spindle fibers begin to interact with newly copied chromosomes
NO
T
MIT
OS
ISM
ITO
SIS
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METAPHASE – Chromosomes pushed by spindle fibers to the metaphase plate ready to be separated
ANAPHASE –Chromosomes separate into two genetically identical groups, move to opposite ends of the cell.
TELEPHASE - Nuclear membranes form around each of the two sets of chromosomes, the chromosomes begin to spread out, and the spindle fibers begins to break down
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CYTOKINESIS –
cell divides into 2 (READY TO START AGAIN)
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http://www.youtube.com/watch?v=nPG6480RQo0&feature=related
http://www.youtube.com/watch?v=VlN7K1-9QB0
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QUICK REVIEW
An in-between time in a cells life where it doubles its DNA and grows ______________
A time in a cells life when the chromosomes condense and become visible also the spindles start to form ____________________
A time in a cells life cycle when spindle fibers finally get to interact with the newly condensed chromosomes because the nucleus just dissolved __________________
interphase
prophase
prometaphase
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QUICK REVIEW
When chromosomes are pushed to the middle of the cell. ____________________
Chromosomes begin moving AGAIN but this time away from each other and towards the opposite sides of the cell. ____________
Nuclear membranes form around each of the two new sets of chromosomes, this is the END of the line ____________
Cells move away from each other _________
metaphase
anaphase
telophase
cytokenisis
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QUICK REVIEW
This phase is NOT part of mitosis ________interphas
e
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INT
ER
PH
ASE
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PR
OP
HA
SE
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PR
OM
ET
AP
HA
SE
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ME
TA
PH
ASE
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AN
AP
HA
SE
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TE
LO
PH
ASE
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CY
TO
KIN
ESIS
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INT
ER
PH
ASE
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A TOUR OF DNA
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Here is a eukaryotic cell (animal cell)
DNA
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The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding.
DNA Packing
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THE CHROMOSOME
THE CENTROMERE
c
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It’s like a
super belt
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A Chromosome
- (1 continuous piece of DNA)
- (a single chromatid)
ALSO a chromosome
- (2 identical continuous pieces of DNA connected at centromere)
-(made of 2 sister chromatids)
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QUICK REVIEW
DNA DOUBLE HELIX
HISTONE
NUCLEOSOME
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QUICK REVIEW
= a chromosome
= a chromosome
OR
2 identical sister ……
chromatids
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• Genes = a unit of heredity passed on from a parent to its offspring
– are written in the language of DNA
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WHERE IS A GENE?!?!?!?!
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• Chromosomes:
– Are made of DNA and histones (protein to wrap DNA around)
– Are not visible in a cell until the chromatin condenses (folds) to the stereotypical chromosome shape.
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ORGANIZE FROM THINNEST (1) TO THICKEST (5)
histones
DNA double helix
Super coil
Chromosomes (coiled)
Nucleosomes
1
2
3
4
5
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INT
ER
PH
ASE
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PR
OR
PH
ASE
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PR
OM
ET
TA
PH
ASE
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Eukaryotic Chromosomes
The number of chromosomes in a
eukaryotic cell depends on the species.
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RED VISCACHA RAT
JK
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Karyotype = A picture of your
condensed chromosomes
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A karyotype
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Remember: this picture is of condensed chromosomes
also
we know, from mitosis, that chromosomes don’t condense unless they were first doubled
(during S of interphase)
So
Look close. . .
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Each chromosome is really made up of it’s “identical twin” from when
it doubled in S of interphase
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For example: If this is mom’s #1 chromosome with information on how her childs eyes will be colored
Your dad has the same #1 chromosome with his version of how to color his child’s eye color
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=
CLOSER INSPECTION
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Each “identical twin” joined at the centromere is known as a chromatid
Here we see 4 chromatids in total, of 2 chromosomes
2 chromatids on the left chromosome (from mom) & 2 chromatids on the right chromosome (from dad)
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Sister chromatids = 2
chromatids joined at
the centromere
s
Here we see ________ pairs of sister chromatids.
2
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=
Homologous chromosomes = moms version of chromosome next to dads version of that same chromosome
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22 PAIRS OF CHROMOSOMES
(44 CHROMOSOMES + 2 sex chromosomes ) = 46
total chromosomes
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A healthy human has a total of 46 chromosomes
or
___ pairs of chromosomes & 2 sex chromosomes
22
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A healthy human has 2 kinds of chromosomes:
1)Autosome = any chromosome that is not related to gender
(chromosome #’s 1 - 44)
2)Sex chromosome = the 2 chromosomes that are related to gender
(chromosome #’s 45 & 46 or x & y)
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MEIOSIS
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WHAT IS MEIOSIS? (NOT MITOSIS)
• meiosis (pronounced my-o-sis) is a process that reduces the number of chromosomes per cell in half. (46 -> 23)
• Meiosis always results in the formation of gametes, (sperm or egg)
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Q – What is the point of meiosis? EXPLAIN!!
Q – What happens to the future cells if a sex cell undergoes mitosis instead of meiosis? EXPLAIN!!
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Q: What is the point of Meiosis?
A: To prepare for sexual reproduction
Q: But why does meiosis have to be different than mitosis?
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Every person is made of cells
Each cell in our body has 46 chromosomes
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A SEXUALLY MATURE MALE AND FEMALE
WANT TO HAVE A BABY
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MALE
•He has 46 chromosomes
per cell
FEMALE
•She has 46 chromosomes
per cell
Without meiosis, a baby would have 92
chromosomes (46 from mom & 46 from dad)
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Remember: meiosis is a process that
cuts the number of chromosomes in
half (46 -> 23)
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QUICK REVIEW
How many chromosomes does a body cell have? _______
How many chromosomes does a cell have before MITOSIS? __________
How many chromosomes does a cell have after MITOSIS? __________
How many chromosomes does a cell have before MEIOSIS? __________
How many chromosomes does a cell have after MEIOSIS? __________
46
46
46
46
23
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Fertilization
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• Dad’s sperm = ___ chromosomes
• Mom’s egg = ___ chromosomes
FERTILIZATION = fusion of sperm and egg
23
23
46 total
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=
MOM (23 chrom) DAD (23 chrom)
+
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From
dad
YOU (46 chromosomes per cell)
From
mom
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The instant just before YOU (becoming 46 chrom’s)
23 chromosomes
23 chromosomes
And ever since this moment each cell in you has been copied
through the process of _________
mitosis
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You divided … and divided…. And divided
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MEIOSIS
(ABREVIATED)
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MEIOSIS VIDEO
http://www.youtube.com/watch?v=D1_-mQS_FZ0
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* REMEMBER *
• Meiosis = reduces the number of
chromosomes per cell in half. (46 -> 23)
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What meiosis looks like
I P P M A T C P P M A T CMEIOSIS I MEIOSIS III I I I I
II II II II II II
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STARTS WITH ENDS WITH
MITOSIS
•1 CELL
•46 CHROMOSOMES PER CELL
•2 CELLS
•46 CHROMOSOMES PER CELL
MEIOSIS
•1 CELL
•46 CHROMOSOMES PER CELL
•4 CELLS
•23 CHROMOSOMES PER CELL
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ABREVIATED REVIEW
OF MITOSIS
I
P
P
M
A
T
C
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ABREVIATED REVIEW OF
MEIOSIS
I
P
P
M
A
T
CP
P
M
A
T
C
MEIO
SIS
IM
EIO
SIS
II
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I
P
P
M
A
T
C
I
P
P
M
A
T
C
MEIO
SIS
I
P
P
M
A
T
C
MEIO
SIS
IIM
ITO
SIS
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MEIOSIS I
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MEIO
SIS
IINTERPHASE (G1)
23 chromosomes from mom
23 chromosomes from dad
I
P
P
M
A
T
C
46 total
* Note = chromosomes are not really condensed *
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MEIO
SIS
IINTERPHASE (S)
23 chromosomes from mom
23 chromosomes from dad
I
P
P
M
A
T
C
46 total
S = synthesis (each chromosome copies itself)
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MEIO
SIS
IINTERPHASE (G2)
23 chromosomes from mom
23 chromosomes from dad
I
P
P
M
A
T
C
46 total
G2 = gap 2
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MEIO
SIS
IMEIOSIS I - ( Prophase I )
23 chromosomes from mom
23 chromosomes from dad
I
P
P
M
A
T
C
46 total
Centrosomes begin to form
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MEIO
SIS
IMEIOSIS I – ( Prometaphase I )
23 chromosomes from mom
23 chromosomes from dad
I
P
P
M
A
T
C
46 total
Nucleus breaks up and spindle fibers rush in
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MEIO
SIS
IMEIOSIS I – (Metaphase I )
23 chromosomes from mom
23 chromosomes from dad
I
P
P
M
A
T
C
46 total
Tetrad’s (homologous chromosomes) line up side by side
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ZOOMING IN
Tetrad = the combination of 2 homologous chromosomes lined up RIGHT next to each other
Dad’s #1 chromosome
Mom’s #1 chromosome
Dad’s #2 chromosome
Mom’s #2 chromosome
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Also, when the homologous chromosomes get this close (a tetrad) some of their information gets switched or CROSSES OVER.
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MEIO
SIS
IMEIOSIS I – (Anaphase I )
23 chromosomes
to the left
I
P
P
M
A
T
CBecause of all the “crossing over” it is impossible to
call one side mom’s and one side dad’s
23 chromosomes
to the right
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MEIO
SIS
IMEIOSIS I – (Telophase I )
23 chromosomes
to the left
I
P
P
M
A
T
CNote: chromosomes begin to unwind (not shown)
and nucleus reforms
23 chromosomes
to the right
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MEIO
SIS
IMEIOSIS I – (Cytokenisis I )
23 chromosomes to the left cell
I
P
P
M
A
T
CEnd of meiosis I
23 chromosomes to the right cell
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MEIOSIS II
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MEIO
SIS
IIMEIOSIS II – (Prophase II )
23 chromosomes to the left cell
P
P
M
A
T
CCentrosomes begin to form (NO INTERPHASE!)
23 chromosomes to the right cell
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MEIO
SIS
IIMEIOSIS II – (Prometaphase II )
23 chromosomes to the left cell
P
P
M
A
T
CSpindle fibers make first contact with
chromosomes as nucleus breaks up
23 chromosomes to the right cell
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MEIO
SIS
IIMEIOSIS II – (Metaphase II )
23 chromosomes to the left cell
P
P
M
A
T
CChromosomes line up at metaphase plate
23 chromosomes to the right cell
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MEIO
SIS
IIMEIOSIS II – (Anaphase II )
23 chrom’S
P
P
M
A
T
CSNAP!!!
23 chrom’S
23 chrom’S
23 chrom’S
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ZOOMING IN ON METAPHASE II
3 CENTROMERES = 3 CHROMOSOMESor 6 chromatids or 6 sister chromatids
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ZOOMING IN ON ANAPHASE II
CE
NT
RO
ME
RE
S
6 CENTROMERES = 6 CHROMOSOMESor 6 chromatids
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MEIO
SIS
IIMEIOSIS II – (Telophase II )
23 chrom’s
P
P
M
A
T
CChromosomes unwind and nucleus reforms
23 chrom’s
23 chrom’s
23 chrom’s
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MEIO
SIS
IIMEIOSIS II – (Cytokenesis II )
23 chrom’s
P
P
M
A
T
CChromosomes unwind
23 chrom’s
23 chrom’s
23 chrom’s
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If you’re a male this happens
SPERM
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EGGS
If you’re a female this happens
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SO…… HERE IS A COMPARISON OF THE TWO
STARTS WITH ENDS WITH
MITOSIS
______ CELL
____ CHROMOSOMES . PER CELL
_____ CELLS
____ CHROMOSOMES . PER CELL
MEIOSIS_____ CELL
____ CHROMOSOMES . PER CELL
_____ CELLS
____ CHROMOSOMES . PER CELL
46 46
46 23
41
1 2
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All non-sex cells are called somatic cells
Sperm and egg cells are called gametes
Lets simplify
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Lets simplify….. even more
n = information
23 chromosomes = n (or haploid)
46 chromosomes = 2n (or diploid)
OR HALF THE INFORMATIONO
OR DOUBLE THE INFORMATION
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=
MOM (23 chrom) DAD (23 chrom)
+
“n” or haploid “n” or haploid
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From
dad
YOU (46 chromosomes per cell)
From
mom
“2n” or diploid
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Parent cell 46 (chromosomes)
mitosis
46
46
Meiosis I
23
23 23 23 23
23
Meiosis II
DIPLOID CELLS (2n)
HAPLOID CELLS (n)
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Parent cell 46 (chromosomes)
mitosis Meiosis I
Meiosis II
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( Diploid 2n)
HAPLOID (n) = 3
HAPLOID (n) = 8
HAPLOID (n) = 11
HAPLOID (n) = 15
HAPLOID (n) = 20
HAPLOID (n) = 23
HAPLOID (n) = 27
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THE BIG DIFFERENCES
1. THE OUT COME
A. MITOSIS = 2 IDENTICAL DAUGHTER CELLS
B. MEIOSIS = 4 DIFFERENT DAUGHTER CELLS (WITH HALF THE GENETIC INFO AS PARENT CELL)
2. METAPHASE I (OF MEIOSIS I)
A. TETRADS LINE UP & CROSSING OVER OCCURS
3. THE NUMBER OF TIMES “PPMAT” HAPPENS
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Genetic Variation
• Without CROSSING OVER offspring of the parents would not be a blend of both parents but a clone !!!
This is not the adult
dog’s puppy
IT IS ITS
CLONE ! ! ! !
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Crossing Over
• In crossing over,
– Homologous chromosomes exchange genetic information.
– Genetic recombination occurs.
Crossing Over
Nondisjunction
• nondisjunction = not separate
– a chromosome pair fail to separate during an anaphase.
– The result is gametes (sex cells) with an incorrect number of chromosomes (too much or too few).
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(MITO
SIS)
METAPH
ASE
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AN
AP
HA
SE
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TE
LO
PH
ASE
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CY
TO
KIN
ESIS
THE END RESULT ARE 2 CELLS THAT SUCK AND ARE ULTIMATELY DESTROYED
Figure 8.20
Figure 8.21
The result of nondisjunction in (meiosis)
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Down Syndrome: An Extra Chromosome 21
• Down Syndrome
– a condition where an individual has an extra chromosome 21.
– also called trisomy 21.
Figure 8.22
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• The incidence of Down Syndrome increases with the age of the mother.
Figure 8.23
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Abnormal Numbers of Sex Chromosomes
• Nondisjunction
– Also affects the sex chromosomes.
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Karyotype = A picture of your
condensed chromosomes
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A karyotype
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A human male karyotype
MALES ARE “XY”
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FEMALES ARE “XX”
A human female karyotype
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Remember: this picture is of condensed chromosomes
also
we know, from mitosis, that chromosomes don’t condense unless they were first doubled
(during S of interphase)
So
Look close. . .
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Each chromosome is really made up of it’s “identical twin” from when
it doubled in S of interphase
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=
CLOSER INSPECTION
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But some times accidents can happen during
cellular reproduction
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Table 8.1
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Mind Blow
n
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Cancer
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What Is Cancer?
• Cancer = a disease of the cell cycle.
• Cancer cells do not respond normally to the cell cycle control system.
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THE CELL CYCLE
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• Cancer cells can form tumors,
TUMORS = Abnormally growing masses of body cells.
–can spread to other parts of the body.
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Cancer Treatment
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• Cancer cells are often grown in culture for study.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
BRAIN GAME
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Imagine a cell with 2 information pieces called chromosomes