Download Meiosis

Do Now 3/11
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1) Why do cells go through the process of
Mitosis?
2) Why do we look similar to our siblings, but
not identical (what could be a logical
explanation of this, even if you don’t know the
scientific answer)?
3) Please take a sheet of paper out, tear it in
half and give one half to your neighbor.
Quiz Time!
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1) Spindle fibers start to disappear, nuclear
membrane forms, and cytoplasm begins to
divide.
2) Each chromatid pair splits at the
centromere and separates to opposite ends of
the cell.
3) Pairs of chromatids line up across the
center of the cell.
Quiz Cont.
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4) Two identical cells are formed.
5) DNA is duplicated.
6) The spindle fibers form.
7) A new nuclear membrane is forming around the
chromosomes.
8)
Name this phase
Meiosis
Please grab a book
and turn to page
548 in your book.
*Take a few minutes
to examine the picture
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• Meiosis - cell division that results in 4 daughter cells,
each with half the number of chromosomes of the
parent cell
• Haploid – Half the # of Chromosomes (n) , 1 of each
pair of chromosomes (23)
• Diploid – 2 of each type of chromosome (2n) , twice
the haploid #
• Homologous Chromosomes – one of two paired
chromosomes, one from each parent
• Synapsis - the pairing of two homologous
chromosomes that occurs during meiosis.
• Crossing Over - homologous chromosomes pair up
with each other and exchange different segments of
their genetic material.
• Somatic Cells - A somatic cell is any biological cell
forming the body of an organism.
• Gametes – Sex cells or reproductive cells
Do Now 3/13
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1) Please list two things you learned
yesterday concerning meiosis.
Sexual Reproduction and Genetics
Meiosis - General Overview
 Human body cells have 46 chromosomes
 Each parent contributes 23 chromosomes
 Takes place in sex cells (gametes)
 One cell becomes 4 NON-IDENTICLE cells
Sexual Reproduction and Genetics
Meiosis – Homologous Chromosomes
Chromosomes and Chromosome Number
 Same length
 Same centromere position
 Carry genes that control the
same inherited traits
 One is from mother, one is
from father = a matching set
Sexual Reproduction and Genetics
Meiosis
Haploid and Diploid Cells
 An organism produces gametes to maintain the
same number of chromosomes from generation
to generation.
 Human gametes contain 23 chromosomes.
 A cell with n chromosomes is called a haploid
cell.
 A cell that contains 2n chromosomes is called a
diploid cell.
Videos to begin and end with
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http://highered.mcgrawhill.com/sites/9834092339/student_view0/
chapter11/meiosis_i.html
http://www.youtube.com/watch?v=D1_mQS_FZ0&NR=1
http://www.youtube.com/watch?v=vA8aM
pHwYh0
Meiosis
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2 Division
• Meiosis I
•
(separation of homologous
chromosomes)
Meiosis II (separation of sister chromatids)
Sexual Reproduction and Genetics
Meiosis
Meiosis I
 Interphase
 Chromosomes replicate.
 Chromatin condenses.
Interphase
Sexual Reproduction and Genetics
Meiosis
Meiosis I
 Prophase I
 Pairing of homologous
chromosomes occurs.
 Each chromosome consists of two
chromatids.
 The nuclear membrane breaks down.
 Spindles form.
Prophase I
Sexual Reproduction and Genetics
Meiosis
Meiosis I
 Prophase I
 Crossing over produces exchange of genetic
information.
 Crossing over—chromosomal segments are
exchanged between a pair of homologous
chromosomes.
Sexual Reproduction and Genetics
Meiosis
Meiosis I
 Metaphase I
 Chromosome
centromeres attach
to spindle fibers.
Metaphase I
 Homologous chromosomes line up at the
equator.
Sexual Reproduction and Genetics
Meiosis
Meiosis I
 Anaphase I
 Homologous
chromosomes
separate and move
to opposite poles of the cell.
Anaphase I
Sexual Reproduction and Genetics
Meiosis
Meiosis I
 Telophase I
 The spindles
break down.
Telophase I
 Chromosomes uncoil and form two nuclei.
 The cell divides.
Sexual Reproduction and Genetics
Meiosis
Meiosis II
 Prophase II
 A second set of
phases begins
as the spindle fibers forms and the
chromosomes condense.
Prophase II
Sexual Reproduction and Genetics
Meiosis
Meiosis II
 Metaphase II
 A haploid number
of chromosomes
line up at the equator.
Metaphase II
Sexual Reproduction and Genetics
Meiosis
Meiosis II
 Anaphase II
 The sister
Anaphase II
chromatids are
pulled apart at the centromere by spindle
fibers and move toward the opposite poles
of the cell.
Sexual Reproduction and Genetics
Meiosis
Meiosis II
 Telophase II
 The chromosomes
Telophase II
reach the poles, and
the nuclear membrane and nuclei reform.
Sexual Reproduction and Genetics
Meiosis
Meiosis II
 Cytokinesis results in
four haploid cells,
each with n number of
chromosomes.
Cytokinesis
Sexual Reproduction and Genetics
Meiosis
The Importance of Meiosis
 Meiosis consists of two sets of divisions
 Produces four haploid daughter cells that are
not identical
 Results in genetic variation
Sexual Reproduction and Genetics
Meiosis
Meiosis Provides Variation
 Depending on how the
chromosomes line up at the
equator, four gametes with
four different combinations
of chromosomes can result.
 Genetic variation also is
produced during crossing
over and during fertilization,
when gametes randomly
combine.
Mitosis vs Meiosis
Do Now 3/14
• Match the description to the phase of meiosis.
1. Sister Chromatids are pulled apart.
_____
A. Prophase I
2. Homologous chromosomes line up
in the middle of the cell._____
3. 2 daughter cells are formed ____
B. Metaphase I
4. Nuclear membrane disappears__
D. Anaphase II
5. Nuclear membrane reforms around
4 cells ____
6. Homologous chromosomes are
pulled apart ____
E. Anaphase I
C. Telophase I
F. Telophase II
Do Now 3/17
• 1) List 3 main
differences
between mitosis
and meiosis (don’t
just talk about the
stages, give
examples!)
• 2) List 3 main
similarities
between mitosis
and meiosis (don’t
just talk about the
stages, give
examples!)
Do Now 3/18
• 1) Did you possess • Which trait
more dominant or
surprised you the
recessive traits
most and why?
based on the ws?
Directions
• Observe the data on the white boards. When
finished with the quiz please create a bar
graph that represents the data, dominant
and recessive traits. Remember, you must
include both dominant and recessive traits.
• Helpful Hint – Y axis contains # of students
while the X axis contains your traits.
– What did you learn from the data?