Transcript Meiosis - Sonoma Valley High School

Cell
Reproduction
Chromosome
Structure
Modern Biology
Pages 144 - 147
• Eukaryotic cells
have their DNA in
structures called
chromosomes.
A cell’s chromosomes
Chromosome
Structure
Modern Biology
Pages 144 - 147
• If the nucleus of
your cell is the size
of a basketball, the
DNA would be 40
miles long!
E. coli “spills” it’s DNA
Chromosome
Structure
Modern Biology
Pages 144 - 147
• Chromosomes:
– Contains a single
DNA molecule.
– Have the DNA
wrapped around
proteins called
histones.
Chromosome structure
Chromosome
Structure
Modern Biology
Pages 144 - 147
• Chromosomes
condense only for cell
reproduction.
• Condensation:
– Twist
– Become shorter
– Become thicker
– Become visible
• Chromosomes can be
moved about cell
easier.
Chromosome condensation
Chromosome
Structure
Modern Biology
Pages 144 - 147
• Prior to cell
reproduction
chromosomes
replicate.
• Each copy is called a
chromatid.
• Sister chromatids are
connected by a
centromere
Centromere
Chromosome
Numbers
Modern Biology
Pages 144 - 147
• Each species has
characteristic
number of
chromosomes.
–
–
–
–
Humans = 46
Fruit flies = 8
Crayfish = 200
Chimpanzee = 48
Fruit fly chromosomes
Chromosome
Numbers
• Chromosomes are
arranged in pairs
called homologous
pairs.
Modern Biology
Pages 144 - 147
Chromosome
Numbers
• One pair
determines sex:
sex chromosomes.
• All others are
called autosomes.
Wednesday 12/3
Pages 144 - 147
Sex
Chromosomes
Modern Biology
Pages 144 - 147
• Either X or Y.
– XX creates
female.
– XY creates
male.
Sex Chromosomes
Haploid Vs
Diploid
Modern Biology
Pages 144 - 147
• A karyotype shows
all homologous pairs
matched on a sheet.
• Sex chromosomes
are paired
separately
Human female karyotyes
• Name two materials that make up chromosomes.
• Histones and DNA.
• What structure connects chromatids once the
DNA (chromosome) has replicated?
• Centromere
• What term describes all chromosomes in a cell
that are identical in males and females?
• Autosomes
• What term describes the pair of chromosomes
that are different in males and females?
• Sex chromosomes
• What does the term “haploid” tell you about a
cell? Diploid?
• One of each chromosome pair.
• Homologous pairs of chromosomes.
Haploid Vs
Diploid
Modern Biology
Pages 144 - 147
• All cells except gametes
have pairs of
chromosomes.
– Diploid
• Sperm and egg
(gametes) have one of
each pair.
– haploid
Human sperm at the
surface of an egg
Cell Division
Modern Biology
Pages 148 - 149
• All cells are
derived from
division of preexisting cells.
• Cell division is
different in
prokaryotes and
eukaryotes.
Prokaryotic cell reproducing
Cell Division in
Prokaryotes
•
•
Prokaryotes reproduce
by binary fission.
Steps in prokaryote
binary fission.
– Chromsome
replicates
– Cell grows
– New cell wall
develops
– Cell splits into two
cells
Modern Biology
Pages 148 - 149
Binary Fission
Cell Division in
Eukaryotes
Modern Biology
Pages 148 - 149
• Two types of cell
division:
• Mitosis: Results in two
daughter cells identical
to the original mother
cell.
• Meiosis: Production of
sperm and egg with 1/2
the chromosomes.
Mitosis in eukaryotic cells
Cell Cycle
Modern Biology
Pages 148 - 149
• G1 Phase
– Cell growth,
normal activity
• S Phase
– Replication of
DNA
• G2 Phase
– Growth for cell
reproduction.
• Mitosis
• Cytokinesis
Eukaryotic cell cycle
Interphase
Modern Biology
Pages 148 - 149
• Consists of G1,
S, G2.
• Cell spends most
time in
interphase.
• Cells may enter
G0 phase.
– Do not reproduce.
Interphase
Stages of Mitosis
Modern Biology
Pages 148 - 149
• Preparation of
the nucleus for
binary fission.
• Continuous
process divided
into four stages.
Cells in phases of mitosis
Stages of Mitosis
Modern Biology
Pages 148 - 149
• Prophase
– DNA shortens and
thickens.
– Two centrosomes
appear with two
centrioles.
– Nuclear envelope
breaks down.
– Centrioles move to
opposite poles.
– Spindle fibers are
produced.
Cells in prophase
Stages of Mitosis
Modern Biology
Pages 148 - 149
• Metaphase
– Chromosmes are
moved to center of
cell.
– Kinetichore fibers
move chromosomes.
– Fibers are
connected to
kinetichore.
– Polar fibers run
from centrosome
to centrosome.
Metaphase
Stages of Mitosis
Modern Biology
Pages 148 - 149
• Anaphase
– Centromere
splits.
– Chromosomes
separate.
– Each copy moves
to opposite pole.
Anaphase
Stages of Mitosis
Modern Biology
Pages 148 - 149
• Telophase
– Chromosomes
become long and
slender.
– New nuclear
envelope forms.
– Nucleolus forms.
– Spindle fibers
breakdown.
Telophase
Plant Vs Animal Mitosis
Plant Interphase
Friday 12/5
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Animal Interphase
Plant Vs Animal Mitosis
Plant Prophase
Friday 12/5
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Animal Prophase
Plant Vs Animal Mitosis
Plant Metaphase
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Animal Metaphase
Plant Vs Animal Mitosis
Plant Anaphase
Friday 12/5
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Animal Anaphase
Plant Vs Animal Mitosis
Plant Telophase
Friday 12/5
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Animal Telophase
Meiosis
Meiosis
• Meiosis is a process by which the chromosome
number is reduced by half.
–Only occurs in testes and ovaries.
–Only occurs in cells called “germ” cells.
–Used to produce sperm and eggs.
• Chromosomes in
all cells of all
organisms are in
pairs referred
to as
homologous
pairs.
• These pairs
must be split
during the
process of
meiosis
Meiosis (cont)
Prior to the Process Meiosis
• Cells undergo the
phases G1, S, & G2
prior to meiosis.
• Cells that undergo
meiosis start as diploid
(2n) cells.
• Meiosis results in four
haploid (1n) cells being
produced.
• Meiosis is known as
“reduction and
division”
• Chromosomes # is
reduced from 2n to
1n.
• Divisions of the cell
result in 4 cells being
produced.
• A diploid cell (2n)
has a pair of each
chromosome.
• These pairs are
referred to as
homologous.
• One “homologue” of
a pair came from
mom and the other
from dad.
• After meiosis
is complete
only one of
each type of
chromosome
is present in a
sperm or egg.
• Prophase I
– Homologous pairs
align with each
other.
– Synapsis occurs.
– Synaptonemal
complex holds
homologues in
place.
– Crossing over
occurs. (At
chiasma)
Meiosis I
• Metaphase I
– Microtubules
attach only to
outside
kinetochores.
– Homologous
pairs move to
equator of cell
due to
kinetochore
fibers.
Meiosis I
• Anaphase I
– Homologues are
pulled apart by
kinetochore
fibers.
– Homologous pairs
are separated
and moved to
opposite poles.
Meiosis I
• Telophase I
– Cell goes
through
cytokinesis.
– Cells are
now 1n or
haploid.
Meiosis I
• Prophase II
– No
replication
– No
synapsis
– No
crossing
over.
Meiosis II
Meiosis II
Centromeres eventually
split.
Chromosomes
are moved to
poles of cell.
A second division
occurs.
Crossing Over
• Crossing over
occurs during
tetrad positioning
of chromosomes.
• Results in genetic
recombination
Crossing Over
• Actual picture of chromosomes crossing over.
• This creates variation among offspring of a species.
Contrasting Mitosis & Meiosis
• Mitosis
– Occurs each time a
“body cell” replicates
– Homologues are
randomly distributed
across metaphase plate
– Crossing over never
occurs.
– Sister chromatids
remain identical.
– Sister chromatids
separate in anaphase I.
• Meiosis
– Occurs only in germ
cells of ovaries and
testes.
– Homologous pairs align
(synapsis)
– Crossing over occurs.
– Sister chromatids are
genetically different
– Sister chromatids do
not separate in
anaphase I
Comparing Mitosis and Meiosis
Embryology
Modern Biology
Pages 682 - 684
• Spermatogenesis
results in 4 mature
sperm from each
germ cell.
• Meiosis reduced the
chromosome number
from pairs (diploid)
to 1 of each
homologous pair (1n).
There are 23 chromosomes in
the human sperm. It will contain
22 autosomes and either an “X”
or a “Y” sex chromosome
Embryology
Modern Biology
Pages 682 - 684
• Oogenesis creates
haploid eggs.
• The egg contains
22 autosomes and
an “X” sex
chromosome.
• The egg also
contains a polar
body.
The egg and the polar body. The polar
body will be expelled if fertilization
occurs
Embryology
Modern Biology
Pages 682 - 684
• 1n egg is fertilized
by 1n sperm.
• 2n zygote is
formed.
• The zygote is a
single cell.
• The zygote then
goes through
mitosis and
cytokinesis.
A fertilized egg with
two nuclei about to fuse
Embryology
Modern Biology
Pages 682 - 684
• Each set of cell
divisions are
referred to as
cleavage.
• Each set of
divisions reduces
the cell size.
• Cleavage
increases the
surface area to
volume ratio.
The zygote has just cleaved to
form a 2 cell morula.
Embryology
Modern Biology
Pages 682 - 684
• Successive
cleavages create
4,8, 16, 32, and 64
cell embryos.
• Embryo called a
morula at this
stage.
• Embryo remains
same size.
Another cleavage
results in 4 cell morula.
Embryology
Modern Biology
Pages 682 - 684
• The embryo then
takes on the shape of
a hollow ball.
• Blastula is composed
of a single cell layer.
– Ectoderm
• Embryo is still the
same size as the
fertilized egg.
Blastula
Embryology
Modern Biology
Pages 682 - 684
• The blastula then
folds inward to
form a gastrula.
• This process is
gastrulation.
• The embryo now
has 2 cell layers.
– Inner “endoderm”
– Outer “ectoderm”
An embryo going through gastrulation.
The most dangerous time of our lives.
Embryology
Modern Biology
Pages 682 - 684
• A third cell layer
develops between
the ectoderm and
endoderm.
– Mesoderm.
• Germ layers
develop into
different organ
systems.
A fully formed gastrula with an
ectoderm and an endoderm
Embryology
Modern Biology
Pages 682 - 684
• Ectoderm
– Skin and nervous
system.
• Endoderm
– Lining of digestive
system.
• Mesoderm
–
–
–
–
Everything in between.
Muscles
Bones
Circulatory system
Human fetus just a few weeks old
and just a couple of inches in length
• Using your notes and directed reading 8.1
complete the following quick write;
• Explain the structure of a chromosome
such as those found in the human cell.
• Contrast sex chromosomes and autosomes.
• Contrast a haploid cell and diploid cell in
terms of chromosomes. Give examples of
each type.