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Meiosis
The Diploid Cell
Cell with ___ sets of chromosomes
Contains chromosomes for each _________ pair
__________ = Body Cells: Diploid
All human cells except ___________ are diploid
Where does the diploid number come from?
____, where n is the number of chromosomes an
individual has
What is n for humans? ______ 2n? ______
The Haploid Cell
Cell containing ___ of each kind of chromosome
Examples: ___________________
___ set of chromosomes
_____ the number of chromosomes of diploid
___
Sperm + Egg = Zygote
Haploid = one of each kind
Diploid = two of each kind
+
•
2n = diploid
or
n = haploid
•
Mitosis vs. Meiosis
Mitosis: t = two: Diploid
2n=46
•
Meiosis: o = one: Haploid
•
n=
23
Meiosis
__________ are produced in specialized
body cells
Sperm and Egg Cells
__ divisions: _______________________
Meiosis occurs in ____ cells, not _____ cells
__ daughter cells
Each cell has ____ the chromosomes of the
parent
Meiosis I
Interphase occurs: the
cell grows and DNA
replicates
Meiosis I begins
Original cell produces
two new cells
Like Mitosis
Prophase I
DNA Coils tightly into chromosomes
Spindle fibers appear
Each chromosome lines up next to the
homologue
Synapis occurs: pairing of homologous
chromosomes
Tetrad: Each pair of homologous
chromosomes
Crossing Over
Crossing Over: why we do not look exactly
like our parents.
•
Portions of the ___________ breaks off and
attaches to _______________ on the
_____________ chromosome
Permits __________________________
between maternal and paternal chromosomes
Occurs during _____________
•
Genetic Recombination
Crossing over
produces a new
mixture of
genetic material
Causes of Variation
Chromosomes are assorted randomly
Crossing over may occur
Cells do not have identical genetic info as
each other or the parent
+ ____________________________
- _____________________________
Metaphase I
Tetrads line up
randomly along the
mid-line
Spindle fibers
attach to
centromeres
Anaphase I
Homologous
chromosomes move
to the opposite poles
Random separation
or Independent
Assortment results in
separation of
maternal and paternal
chromosomes.
Telophase I
Chromosomes
reach opposite
ends of cell
Cytokinesis
begins
Cell is now
haploid
Meiosis II
Occurs in each
cell formed in
Meiosis I
Interphase does
not occur again
Prophase II
Spindle fibers
form and move
the
chromosomes to
the mid-line of
the dividing cell
Metaphase II
Chromosomes
move to the midline of the dividing
cell facing
opposite poles of
the dividing cell
Anaphase II
Chromatids
separate and
move to
opposite poles
of the cell
Telophase II
Nuclear membrane forms around the chromosomes
in each of 4 new cells
Cytokinesis II
__________ divides
____________________ closes off
End Result:
____ new cells that contain _____ of the
original cells number of chromosomes
Creates _________ = _________
What exactly is a gamete?
Formed by ________
___________________ cells
In humans, meiosis occurs in
the testes and ovaries
Meiosis Animation
•
Meiosis Animation
Why do we need haploid gametes?
•
Female gamete
Male gamete
23
23
EGG
SPERM
Fertilization restores the diploid number
1n
fertilization
1n
meiosis
2n
2n
Mitosis and
cell growth
2n
Mitosis vs. Meiosis
•
Mitosis vs. Meiosis Animation
Notes:
Nondisjunction
•
•
Failure of ___________________ to
___________ properly during meiosis.
__________________ of a homologous
pair move to the ____________ of the cell.
•
1 gamete has ___________________
•
•
Or
1 gamete is ______________________
Nondisjunction Animation
•
Nondisjunction Animation
Notes:
Chromosome Pop Quiz!
•
What is a chromosome?
•
Where do we find them?
•
What do they look like?
•
•
How many pairs of chromosomes do
humans have?
What determines if someone is male or
female?
Trisomy: Extra Chromosomes
•
Trisomy 13: Patau’s Syndrome
•
Trisomy 21: Down’s Syndrome
•
XXX: Trisomy X
•
XYY: Jacob’s Syndrome
•
XXY: Klinefelter’s Syndrome
Monosomy: Missing Chromosomes
•
•
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Most do not survive.
Turner XO : develop as girls,
but infertile
OY: lethal