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BELLWORK:
1. Mitosis occurs in what type of cells in our body?
______________ cells
2. Meiosis occurs only in our ________________
http://www.youtube.com/watch?v=hVUKoEFYClo
B ELLWORK :
Draw and write the name of each numbered item:
1. _______________
2. _______________
3. _______________
4. _______________
5. _______________
6. What phase of
mitosis is this cell
in?_____________
BELLWORK: Thurs. OCT. 29, 2015
Cell are limited in size by ____________ and
______________
2.
_________ cells can become any type of cell
3.
_________________ hold sister chromatids
together.
4.
A chromosome consists of 2 identical
sister _____________________
1.
WHY DO CELLS DIVIDE (“DO MITOSIS”…)
One-celled organisms:
for reproduction
 asexual reproduction (clones)

amoeba
Multi-celled organisms

for growth and development
 from fertilized egg to adult

for repair and replacement
 replace cells that die from normal wear
& tear or from injury
starfish
GETTING FROM THERE TO HERE…
 Going
from egg to baby….
the original fertilized egg has to divide…
and divide…
and divide…
and divide…
But how did
it all start???
But how did the egg cell and the sperm cell end up
with half each (23) the normal human number of
chromosomes (46) … so you didn’t have too many?
11.4 MEIOSIS
11-4 MEIOSIS
meiosis
Chromosomes: strands of DNA
and protein inside the cell
nucleus  are the carriers of
genes.
Genes: are located in specific
positions on chromosomes.
An organism must inherit a single
copy of every gene from each of
its “parents.”
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So…Gametes are
formed by a process
that separates the two
sets of genes so that
each gamete ends up
with just one set.
This makes the sperm
cell and the egg cell…
Gametes when the two sets
of genes in an organism are
separated into one set.
The male gamete in
animals is the:
Sperm!!!
In higher plants it is:
Pollen!!!!
The female gamete in
animals is the:
Egg or Ova!!!
In higher plants it is:
Seed or ovule!!!!
Chromosome Number
All organisms have
different numbers of
chromosomes.
Diploid: cell that contains both sets of
homologous chromosomes.
The number of chromosomes in a diploid cell =
2N.
For Drosophila (fruit flies),
the diploid number is 8
Or 2N=8.
A body cell of a human has 46
chromosomes and are DIPLOID.
2N = 46
COMING UP: Our gametes (egg/sperm) have
23 chromosomes and are HAPLOID
N = 23
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All of our body cells are Diploid and
have 46 chromosomes in their
nuclei:
Haploid cells: contain only a single set of
chromosomes, and a single set of genes.
Gametes of sexually reproducing
organisms are haploid.
Remember: Haploid = Half the
chromosome number
Haploid cells are represented by the
symbol N.
For Drosophila (fruit flies) the haploid
number is 4, which can be written as
N=4.
Our gametes (egg/sperm) have 23
chromosomes and are HAPLOID
N = 23
REMEMBER: A body cell of a human has 46
chromosomes and are DIPLOID.
2N = 46
GAMETES
Think of sperm
and eggs as half
cells
23
23
HALF “PLOID”
• A body cell in an adult fruit fly has 8 chromosomes:
4 from the fruit fly's male parent, and 4 from its
female parent.
These sets of chromosomes are homologous.
Each of the 4 chromosomes that came from the male
parent has a corresponding chromosome from the
female parent.
Meiosis
is a reduction division. The
number of chromosomes per cell
is cut in half as homologous
chromosomes separate from a
diploid cell.
Meiosis involves 2 divisions, meiosis I
(PMAT1) & meiosis II (PMAT2)
By the end of meiosis II, the diploid cell
that entered meiosis has become 4
haploid cells.
Meiosis I
Interphase I
Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I
and
Cytokinesis
Cells undergo a round of
DNA replication, forming
duplicate chromosomes.
Interphase I
Crossing over: when homologous chromosomes
form tetrads and exchange portions of their
chromatids in MEIOSIS 1
THIS produces new combinations of alleles –
genes which is why we don’t all look alike!!!!!
from mom
from dad
from mom
from dad
from mom
from dad
Tetrad: when chromosomes
pair with their homologous
chromosome
There are 4 chromatids in a
tetrad.
MEIOSIS I
Prophase I
Spindle fibers attach to the chromosomes.
MEIOSIS I
Metaphase I
Centrioles
The fibers pull the
homologous
chromosomes toward
opposite ends of the
cell.
MEIOSIS I
Anaphase I
Nuclear membranes form.
The cell separates into 2 cells with chromosomes
and alleles that are different from each other and
from the diploid cell that entered meiosis I.
MEIOSIS I
Telophase I and
Cytokinesis
Meiosis II
The 2 cells made by meiosis I enter a 2nd meiotic
division.
Unlike meiosis I, neither cell goes through
chromosome replication.
Each of the cell’s chromosomes has 2 chromatids.
Meiosis II
Telophase I and
Cytokinesis I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
and
Cytokinesis
Meiosis I results in two haploid (N) daughter
cells, each with half the number of
chromosomes as the original cell.
MEIOSIS II: Prophase II
Phases of Meiosis
The chromosomes “meet” orline up in the center
of cell.
MEIOSIS II:
Metaphase II
Phases of Meiosis
The sister chromatids separate and move toward
opposite ends of the cell.
MEIOSIS II
Anaphase II
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Meiosis II results in four
haploid (N) daughter cells.
MEIOSIS II
Telophase II and Cytokinesis
Gamete Formation
In male animals, meiosis results in four equal-sized
gametes called sperm.
In many female animals, one egg results from
meiosis. The other three cells are tiny polar bodies
which basically shrivel up an die
The egg gets most of the
cytoplasm
Comparing Mitosis and Meiosis
Mitosis results in the production of
two genetically identical diploid cells.
Meiosis produces four genetically
different haploid cells.
• meiosis=related
• This starts on page 323
• Due Tuesday but start working
NOW
BELLWORK: FRI. NOV. 12, 2010
1. Meiosis occurs in _____ cells (__________),
produces ___ genetically ____________ cells.
2. Mitosis occurs in _________ cells, produces ___
genetically ____________ cells.
• http://www.pearsonsuccessnet.com/snpap
p/iText/products/0-13-1811185/ch11/ch11_s4_1.html
Comparing Mitosis and Meiosis
Mitosis
• Cells produced by mitosis have the same number
of chromosomes and alleles as the original cell.
• Mitosis allows an organism to grow and replace
cells.
• Some organisms reproduce asexually by mitosis.
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Comparing Mitosis and Meiosis
Meiosis
• Cells produced by meiosis have half the number
of chromosomes as the parent cell.
• These cells are genetically different from the
diploid cell and from each other.
• Meiosis is how sexually-reproducing organisms
produce gametes.
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11-4
Copyright Pearson Prentice Hall
11-4
If the body cells of humans contain 46
chromosomes, a single sperm cell should have
a. 46 chromosomes.
b. 23 chromosomes.
c. 92 chromosomes.
d. between 23 and 46 chromosomes.
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11-4
During meiosis, the number of chromosomes
per cell is cut in half through the separation of
a. daughter cells.
b. homologous chromosomes.
c. gametes.
d. chromatids.
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11-4
The formation of a tetrad occurs during
a. anaphase I.
b. metaphase II.
c. prophase I.
d. prophase II.
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11-4
In many female animals, meiosis results in the
production of
a. only 1 egg.
b. 1 egg and 3 polar bodies.
c. 4 eggs.
d. 1 egg and 2 polar bodies.
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11-4
Compared to egg cells formed during meiosis,
daughter cells formed during mitosis are
a. genetically different, while eggs are
genetically identical.
b. genetically different, just as egg cells are.
c. genetically identical, just as egg cells are.
d. genetically identical, while egg cells are
genetically different.
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