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MEIOSIS
Chapter 11
REVIEW

Cell has issues when it grows larger in size
Not enough DNA
 Nutrients and wastes cannot pass the cell membrane

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Cell solves these problems through the process of
cell division
Mitosis – the portion of cell
division where the nucleus divides
MITOSIS

Almost every cell of the body uses mitosis to
divide the nucleus

Somatic cells – cells that are not sex cells/gametes

Exs) liver cell, bone cell, brain cell etc.
AS LONG AS IT IS NOT SPERM OR EGGS IT
USES MITOSIS

Cell grows (G1), synthesizes
DNA (S), makes molecules
and organelles (G2) and then
is ready for cell division
(mitosis and cytokinesis)
STAGES OF MITOSIS
1.
Prophase – chromatin
condenses into chromosomes
and nuclear envelope breaks
down, centrioles move and
spindle fibers form
2.
Metaphase – chromosomes
line up in middle of cell and
spindle fibers attach to
centromere
PROPHASE
STAGES OF MITOSIS
3.
Anaphase – spindle fibers
pull at centromere and
separate sister chromatids
pulling them to opposite
ends of the cell
4.
Telophase – chromosomes
break down into chromatin
and nuclear envelope
reforms
THE END OF MITOSIS


After telophase, the cells cytoplasm splits by the
process of cytokinesis
As a result we are left with…
2 IDENTICAL DAUGHTER CELLS
THE NEW STUFF…
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There are many studies into the
process that makes each one of us
different
Gregor Mendel – a monk born in
1822 who did many studies in the
field of genetics
Genetics – the study of heredity

Why is it that we have traits (eye
color, hair color, etc.) similar to our
parents, yet we are not all alike?
GENETICS
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Mendel recognized that the offspring of “parents”
were similar and began to investigate why this
happens
He came to the conclusion that the parent
organisms must pass on traits in their genetic
material
These traits are located on
their genes (DNA)
MENDEL’S PREDICTIONS


Mendel was correct about the passing of traits
and the idea of genes
He wasn’t sure how these events happened but
knew
1.
2.
An organism must inherit a single copy of every
gene from both its “parents”
When and organism produces its own cells to pass
to offspring, there are 2 sets that must separate
from each other so that each cell contains just 1 set
of genes
STOP! WHAT DOES THIS MEAN?!?!

Gametes – the sex cells of an organism
Sperm and eggs
 Mitosis deals with non-gametes (somatic cells)


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Remember, in mitosis we result in genetically
identical cells
WE DO NOT WANT GENETICALLY
IDENTICAL OFFSPRING!!!
TRANSLATION OF MENDEL’S IDEA #2
When and organism produces its own cells to pass to
offspring, there are 2 sets that must separate from
each other so that each cell contains just 1 set of
genes

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Every cell of the human body contains a specific
number of chromosomes (46)
In order for offspring to maintain that number of 46
and not end up with duplicate (92), the parent gamete
(sex cell) must half their number of chromosomes
 End
result > 23 (mom) + 23 (dad) = 46 offspring
chromosomes
TRANSLATION OF MENDEL’S IDEA #1
An organism must inherit a single copy of every gene from
both its “parents”


Remember, each of the 46 chromosomes needs to
halved by the parents (to make 23)
Parents will only contribute each of those 23 genes
one time to their offspring
 (parents
do not want to give multiple copies of the same
gene)
 So,
again 23 + 23 = 46 chromosomes total
CHROMOSOMES AND GAMETES
Remember…


Chromosomes – the structures in the cell that
carry the genetic material (genes) from the
parent cell to the daughter cell
Gametes – sex cells or germ cells (sperm and egg)
CHROMOSOMES
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There are many chromosomes in the body that
carry information for many different “things”
Examples – eye color, hair color, height, 2nd toe
length, etc… (everything that makes you, you!)
When 2 cells come together from 2 parents, the
matching chromosomes must come in contact
These matching chromosomes are called
homologus

Homologous Chromosomes – same chromosome types
between mother and father cells
CHROMOSOME NUMBERS
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Haploid – a cell that contains a single set of
chromosomes
Remember “hap” sounds like half
 Is usually represented as N

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Diploid – a cell that contains both sets of
homologous chromosomes
Remember “di” means 2 (kinda like “bi” – bicycle)
 Is usually represented as 2N


Since the somatic cells of the body are diploid we
need the sex cells to be haploid so offspring do
not have more chromosomes than necessary
WHAT DO DIPLOID/HAPLOID NUMBERS MEAN?
Diploid Barbie
2N = 46
chromosomes
Diploid Ken
2N = 46
chromosomes
Haploid Ken Cell
N = 23
chromosomes
Haploid Barbie Cell
N = 23
+
chromosomes
Sperm cell
Egg cell
Equals
Diploid Baby
2N = 46
chromosomes
HOW ARE HAPLOID GAMETES PRODUCED?

Meiosis

a process of reduction division in which the number
of chromosomes per cell is cut in half through the
separation of homologous chromosomes in a diploid
cell

Involves 2 distinct divisions
1.
2.

Meiosis 1
Meiosis 2
Starts with 1 diploid cell and results in 4
haploid daughter cells that are
GENETICALLY DIFFERENT from the
parent cell
MEIOSIS 1

Prior to meiosis 1, each chromosome is replicated

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Same as S phase of interphase prior to mitosis
Meiosis 1 starts with the cell beginning to divide
very similarly to mitosis

Unlike mitosis, meiosis 1 has homologous pairing in
each step

Homologous Pairing – the same chromosome types
from mom and dad come together (eye color, hair
color, etc.)
PROPHASE 1

Homologous chromosomes pair and form a tetrad


Since 1 chromosome is made of 2 chromatids, there
are 4 chromatids in a tetrad
While in their tetrad, homologous chromosomes
are able to trade/swap information in a process
called crossing over
this process results in the exchange of traits (alleles)
between the same chromosomes therefore creating
new trait combinations
 One reason why you are
different from your parents!

REMAINDER OF MEIOSIS 1
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Meiosis utilizes the remainder of the cycles as
mitosis did separating homologous chromosomes
instead of sister chromatids
Metaphase 1 – spindle fibers attach to homologous
chromosomes
Anaphase 1 – spindle fibers separate homologous
chromosomes
REMAINDER OF MEIOSIS 1
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
Telophase 1/Cytokinesis – the nuclear envelope
reforms around chromosomes and the cytoplasm
splits
As a result of Meiosis 1, 2 daughter cells are
produced that have half the number of
genetically different chromosomes
MEIOSIS 2
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After Meiosis 1, the 2 cells produced proceed to
meiosis 2 (there is no chromosome replication)
Each of the daughter cells move through Meiosis
2 much in the same way Mitosis occurs
Prophase 2 – the centriole move
to opposite ends of the cell, the
nuclear envelope breaks down
Metaphase 2 – chromosomes
line up in the middle of the
cell and spindle fibers attach
to the centromere
MEIOSIS 2
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Anaphase 2 – the spindle fibers pull on the
centromere and split the sister chromatids
Telophase 2 & Cytokinesis – the nuclear envelope
forms and the cell cytoplasm splits
4 genetically DIFFERENT cells result
GAMETE FORMATION
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The male gamete that is produced is called a
sperm (spermatocyte)

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There are 4 sperm cells that are produced as a result
of meiosis
The female gamete that is produced is called an
egg (oocyte)
There is 1 egg cell produced as a result of meiosis
 The 3 other cells produced are called polar bodies
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Polar Bodies are not used in reproduction and are
considered to be the trash bags of the egg, but can be useful
in genetic testing
COMPARING MITOSIS AND MEIOSIS
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Sloppy Copy
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Mitosis/Meiosis Picture
Fold paper down middle
 Draw Mitosis on left side starting with interphase
and ending with cytokinesis beginning with 4
chromosomes (X’s)
 Draw Meiosis on right side starting with interphase
and ending with cytokinesis 2 beginning with 4
chromosomes (X’s)
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Mitosis/Meiosis Compare/Contrast Graphic
Organizer
3 ways they are similar
 3 ways they are different
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