Download Chapter 13 - Meiosis and Sexual Life Cycles

Chapter 13 - Meiosis and Sexual Life Cycles
Review: Describe the functions of mitosis.
High frequency quiz mistakes:
1. Incorrect number of chromosomes
used in depiction of mitotic cell
division. Question stated that the cell
was diploid and the haploid number
(n) was 2.
Diploid
Haploid number
(number of chromosomes in a
(2n)
(n)
set)
2 sets
X
2
=
4
chromosome
Chapter 13 - Meiosis and Sexual Life Cycles
Review: Describe the functions of mitosis.
High frequency quiz mistakes:
Practice
A. How many chromosomes in a
triploid cell with a haploid
21number of
7?
B. A diploid cell has 24 chromosomes.
What is the value
12 of n?
C. A 4n cell has 40 chromosomes.
What is the ploidy of this cell and how
Tetraploid, 20
many chromosomes would you expect
Chapter 13 - Meiosis and Sexual Life Cycles
Review: Describe the functions of mitosis.
High frequency quiz mistakes:
Practice
D. Draw a triploid nucleus of a cell
with n = 2.
Chapter 13 - Meiosis and Sexual Life Cycles
Review: Describe the functions of mitosis.
High frequency quiz mistakes:
2. What are the two possible
chromosome combinations found in
human
male
sperm?
- Are the gametes haploid or diploid?
Ans: One of each homologous pair
1 through 22 and X
1 through 22 and Y
Chapter 13 - Meiosis and Sexual Life Cycles
Review: Describe the functions of mitosis.
This brings us to our next
adventure…how are the gametes
made?
Meiotic Cell Division (the other cell division
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Compare asexual to sexual reproduction
Reproduction
A. Asexual
Reproduction
B. Sexual
Reproduction
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Compare asexual to sexual reproduction
A. Asexual
1. One parent
Reproduction
2. Genetically identical offspring (called clones) if we
ignore mutations, which they rely on to evolve.
Made possible by begin able to have numerous offspring very quickly as positive
mutations are rare, but if you have millions of offspring in a few days one likely has
a mutation.
What issuch
a positive
mutation in general?
One that give the organism (vehicle) a better ability to survive and reproduce in current
environment.
3. Single-cell organisms (certain protists [ex. amoeba] and
fungi [ex. yeast] and all prokaryotes [bacteria])
A. Prokaryotic cell cycle (binary fission)
B. eukaryotic cell cycle (“mitosis”)
4. Plants (vegetative propagation) and animals
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Compare asexual to sexual reproduction
B. Sexual
- Two parents
Reproduction
- Gametes produced (fertilization)
- Highly variable offspring due to
mixing of DNA of two parents
- Most eukaryotes
Tend to have fewer offspring over longer
periods of time making mutations not a reliable
means of generating diversity…
…better to shuffle the DNA between two
organisms.
Chapter 13 - Meiosis and Sexual Life Cycles
NEW AIM: Describe how gametes are formed.
Gametes
Somatic cells
Fig. 8.13
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Meiotic cell division
1. Formation of gametes in animals
- Therefore essential for sexual reproduction
2. Formation of spores in plants and fungi
3. Called reduction division
- The number of chromosomes is cut in
half (typically from diploid [2n] to haploid
[n])
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Compare gametes to somatic
cells in terms of chromosome
(Soma- means body; somatic cell = body cell)
number.
Gametes are haploid (have one set of 23 chromosomes in
humans), while somatic cells are diploid (have two sets or 46
chromosomes in humans)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Gametes
Somatic cells
Fig. 8.13
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Review the DNA/chromosomes in a human nucleus…
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Humans have 23 pairs of
chromosomes for a total of 46.
This image shows the
46 chromosomes from
the nucleus of a single
human male cell.
You can see that each
chromosome has a very
similar (homologous)
matching pair with the
exception of the sex
chromosomes (X and Y).
Females would have a
homologous pair of X’s.
Males have an X and a Y (not
homologous).
This display of chromosomes is called a Ka
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Humans have 23 pairs of
chromosomes for a total of 46.
Therefore we have how many of each gene?
Ans: at least two of every gene, except
for the genes on the X and Y
chromosomes in males since these
chromosomes are not homologous.
These are homologous (similar) chromosomes
If the gene for hemoglobin were on one of these (green
bar), then it is on the other as well in the same location
(locus).
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Humans have 23 pairs of
chromosomes for a total of 46.
Every nucleus has 22
pairs of autosomes
(chromsomes 1 through
22)
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Humans have 23 pairs of
chromosomes for a total of 46.
…and one pair of
sex chromosomes
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Humans have 23 pairs of
chromosomes for a total of 46.
What
chromosomes
would have been
found in the sperm
that fertilized the
ovum that was to
*One
ofperson?
each pair
be this
comes from the
mother, and the
other comes from
the father.
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Humans have 23 pairs of
chromosomes for a total of 46.
*Therefore, this is the
DNA that would have
been packaged in the
nucleus of the…
(sperm or egg?)
…father’s sperm that
penetrated and fertilized
the ovum to form a
zygote because only
males have Y
chromosomes.
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Humans have 23 pairs of
chromosomes for a total of 46.
*And this is the DNA
that would have been
packaged in the
nucleus of the
mother’s ovum (has
This
could also be in a
an X).
sperm, but the previous
slide could not be in an
ovum.
Ans: MalesExplain.
are XY. Therefore sperm
can have an X or Y (they determine sex.
Females are XX and therefore the ovum
can only have an X.
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Humans have 23 pairs of
chromosomes for a total of 46.
- One of each of
chromosomes 1
through 22 and a sex
chromosome as
shown to the right is
considered to be one
complete set or n.
The word for this is
haploid.
hap- = one
-ploid = set
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Humans have 23 pairs of
chromosomes for a total of 46.
If I said that human
cells are 2n that
means each cell has
2
how many sets?
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
Humans have 23 pairs of
chromosomes for a total of 46.
If I said that human
cells are 2n that
means each cell has
2
how many sets?
The word for this is
diploid.
di- = 2
-ploid = sets
Humans are diploid organisms.
What are our gametes, ha- or
diploid?
Ans: haploid. When they fuse during
fertilization the resulting zygote is
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
What is “n”?
n is a complete set of
chromosomes (1 of each
chromosome)
n is called the haploid
number
…or number of
chromosomes in a
complete set.
Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles
AIM: Describe the eukaryotic cell cycle.
What is the value of “n”
in humans?
23, because we have 23
chromosomes in one set
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
How and where are the gametes formed in humans?
Gametogenesis - formation of gametes (two type
1. spermatogenesis
-Formation of sperm, occurs in testes
(male gonads)
2. Oogenesis
- Formation of ovum, occurs in ovaries
(female gonads)
This is all meiosis (gametogenesis, spermatogenesis, Oogenesis)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
The variety of sexual life cycles
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Ploidy? n?
Meiotic cell division
This figure shows a simple
diploid cell with one
homologous chromosome
pair (n=1).
Red one is maternal
(coming from mother) and
blue one is paternal
(coming from father).
What will happen first?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Meiotic cell division
DNA will be replicated.
Then what?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Meiotic cell division
Homologous pairs will be
pulled apart.
And lastly?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Haploid (n)
Meiotic cell division
Sister chromatids will be
pulled apart.
Haploid (n)
Diploid (2n)
Each resulting cell is
haploid with one of each
homologous pair!
Diploid (2n)
Meiosis I
(1st division)
Meiosis II
(2nd division)
If you want to add a
second, third or even 23
pairs, they all behave the
same way.
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Meiotic cell division
Overview
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
MEIOSIS (meiotic cell divis
(Gamete/spore formation)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
MEIOSIS (meiotic cell divis
(Gamete/spore formation)
Mitotic cell division (asexual reproduction) would have
evolved first before sexually reproducing organisms,
which require meiosis, came onto the scene…
Reminder: Evolution builds on old ideas (Ex. RNA world
hypothesis)
You might hypothesize then that meiotic cell division
Mitotic
Cell Division.
should be very
similar
to…
General overview to start…
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
MEIOSIS (meiotic cell divis
(Gamete/spore formation, reduction division)
Why is it logical to pair up homologous
chromosomes?
The proteins of the cell are simply programmed to pull
paired up chromosomes apart (life is simple, just a lot of
simple things happening at once making it appear overly
complex)…
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Meiotic cell division (details):
1. Interphase (G1, S, G2)
- Similar to cell cycle (mitotic cell
division) interphase. Use those
notes.
2. Meiosis – two rounds of cell division
a. Meiosis I – first round (PI, MI,
AI,cytokinesis
TI)
b.
c. Interaphase II (interkinesis) - only in certain
species (do not need to include this on test)
d. Meiosis II – second round (PII, MII, AII,
TII)
e. cytokinesis IPMATPMAT
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Interphase (G1, S, G2)
- Similar to cell cycle (mitotic cell
division) interphase. Use those
notes.
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
MEIOSIS I: Separate the homologous pair
Prophase I (longest phase, up to 90% of meiosis)
-Most complex phase of meiosis
-Occupies 90% of meiotic cell
division
-Chromosomes
condense
-Synapsis occurs = homologous
chromosomes come together in
pairs resulting in the formation of
tetrads.
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
MEIOSIS I: Separate the homologous pair
Prophase I
-Crossing over occurs –
homologous chromosomes
exchange equivalent segements
i. This “shuffles” the genes so
that the same genes are not
always together on the
chromosome
ii. This site of crossing over is
called the chiasma
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
MEIOSIS I: Separate the homologous pair
Prophase I
-nucleoli disappear
-centrosomes move to poles
-Spindle begins to form
-Nuclear envelope breaks down
-MTs attach to kinetochores at centromeres
-one pole is attached to one
homologous pair while the other
pole attaches to the other
homologous
pairwith each other
-Free
MTs interact
to elongate cell like in mitosis
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
MEIOSIS I: Separate the homologous pair
Metaphase I
-tetrads align on metaphase plate
(brought there by kinetochore motor
proteins using ATP for fuel)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
MEIOSIS I: Separate the homologous pair
Anaphase I
- Homologous pairs (homologs)
separate as kinetochore proteins
walk along spindle fibers toward
opposite poles
- sisters stay together attached by
centromere
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
MEIOSIS I: Separate the homologous pair
Telophase I
- Homologs arrive at poles
- Each pole now has a haploid (n)
set: remember that sister chromatids
are considered a single
chromosome
Cytokinesis
- Overlaps telophase I
- Similar to cytokinesis in mitotic phase
- Results in two haploid (n) cells
although the amount of DNA is
similar to the starting diploid cell
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
diploid
diploid
diploid
diploid
Haploid
after
cytokinesi
s – each cell
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Meiosis II
separate the sisters
haploid
- Similar to the mitotic phase – separate the sisters
- Meiosis II starts with two haploid cells and forms four haploid
cells with half the amount of DNA
**** Chromosomes do not replicate. Only the
centrosomes replicate during interphase II/prophase
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Why go through all of this trouble (use lots of energy)
to makes gametes, cross-over, find a mate, try and
fertilize an egg to reproduce sexually?
Genetic variation/diversity of offspring
(sexually reproducing organisms do this to mix/shuffle their DNA
resulting in very different offspring genetically so that as the
environment changes, there will inevitably be certain gene
combinations that will survive it.)
Ex. The flu pandemic of 1918 may have killed 50 million people, but
it didn’t kill everyone. Different gene combinations means different
biochemistry and therefore different susceptibility to disease or
other environmental changes. Another example is HIV…
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Why go through all of this trouble (use lots of energy)
to makes gametes, find a mate, try and fertilize an
egg…basically to reproduce sexually?
Genetic variation/diversity of offspring
Evolutionary Trade-offs: realize that it is a trade-off since it
does require more energy to do this and time to find a mate,
etc…
There is almost always a trade-off. Ex) We stand upright on
two legs using skeletons naturally selected to walk on all
fours. Some of the trade offs are back problems, foot
problems, hemorrhoids, and many others…
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Irish Potato Fami
(another example of the importance of genetic dive
Never depend on one crop,
especially one crop of genetically
- Period of mass starvation and disease
in Ireland between 1845 and 1852
~1,000,000 died and another 1,000,000
fled
1/3rd of Irish population depended on
potatoes as major source of food.
Potatoes do not reproduce well from
seed (sexual reproduction) and were
asexually propagated (vegetative
propagation). Therefore, all the potato
plants in Ireland were essentially
genetically identical…clones.
- Potato blight, a disease that destroys
potato plants caused by the fungus
Phytophthora infestans, ripped through
and destroyed all the Irish crops because
all the plants were identical and therefore if
one is susceptible to the disease, they all
are…
Chapter 13 - Meiosis and Sexual Life Cycles
NEW AIM: How do sexually reproducing organisms generate diversity?
When a human male and female conceive a child,
there are greater than 64 trillion possible
outcomes (>64 trillion different possible genetic
combinations in the offspring)
How do sexually reproducing
organisms generate this kind?of
diversity
1. INDEPENDENT ORIENTATION OF CHROMOSOMES
1. INDEPENDENT ORIENTATION OF CHROMOSOMES
Because the tetrads independently and randomly orient
themselves on the metaphase plate during metaphase I, many
different chromosomal combinations can arise:
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How do sexually reproducing organisms generate diversity?
How many different possible
gametes can be generated by a
to the left, the
human?Incelltheis example
diploid with n=2. The
outcome of meiotic cell
division is 4 different
possible combinations.
DIPLOIDS
n
Possible
combinations
2
4
3
8
4
16
5
32
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How do sexually reproducing organisms generate diversity?
How many different possible
gametes can be generated by a
How many chromosomal human?
combinations can be made in the
gametes of a diploid cell (2n= 6), or n =
3?
Let’s call the chromosomes 1m, 1d,
2m, 2d, 3m and 3d. Just make all the
possible gamete combinations
(remember that each gamete will get
on of each homologous pair):
1m, 2m, 3m
1m, 2m, 3d
1m, 2d, 3d
1m, 2d, 3m
1d, 2m, 3m
1d, 2m, 3d
1d, 2d, 3d
1d, 2d, 3m
8 possible
combination
s in the
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How do sexually reproducing organisms generate diversity?
How many different possible
gametes can be generated by a
We can keep playing this game for
human?
n=4, n=5, etc… until we get to humans,
n=23:
DIPLOIDS
n
Possible
combinations
n
Possible combinations (2n)
2
4
2
2n = 4
3
8
3
2n = 8
4
16
4
2n = 16
5
32
5
2n = 32
23
8,388,608
23
2n = 8,388,608
The number of POSSIBLE chromosomal combinations in the gametes of a
diploid organism is 2n where n = haploid number.
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How do sexually reproducing organisms generate diversity?
2. Random fertilization
How many possible sperm
and ovum combinations?
There are 223 different sperm
combinations and 223 different ovum
combinations.
That makes 223 x 223 = 246 different combinatio
246 = ~64 trillion possible combinations
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
You are 1 in 64 trillion
(well…not exactly)
What are we ignoring?
Crossing-over
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
Alleles
A Gene coding for a specific
RNA/polypeptide can have different
versions (slightly different DNA sequences)
possibly resulting in an
RNA/polypeptide/protein with a very similar
functionality, but not identical. These
different gene versions are called alleles.
Allele
C and c are different versions of the same gene. They are
s
alleles. C codes for a protein that will somehow be involved
in making mouse fur black while c will make almost the
same protein, but will be involved in making mouse fur
white. If I showed you a picture of C and c you would not be
able to tell them apart without looking VERY closely.
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
Without crossing-over, C and E would always travel together in the
gametes just as c and e would always be together. If genes are located on
the same chromosome we say they are LINKED.
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
How can these different genes (C and E; c
and e) be unlinked so that C is with e and E
is with c?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
During prophase I, just after
synapsis, crossing over will
occur.
During crossing-over there is a
reciprocal (equal both ways)
chromosomal exchange between
homologous chromosomes
Why must it be an equal exchange?
Each gamete must get one set of
chromosomes will all the necessary
genes. An unequal exchange would
result in some gametes getting too
many genes and some getting too few
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
Reminder: Crossing over occurs
at sites called chiasma and there
can be more than one crossingover per homologous pair…
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
This figure shows
three crossing over
events:
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
Crossing over begins after synapsis (formation of the tetrad) during
prophase I.
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
Enzyme will cut the DNA at the same locus of each homologous
pair…
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
Other proteins will reconnect the chromosome fragments to the
opposite homolog…
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
and meiosis continues as normal...
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
3. Crossing Over
Parental type chromosome (looks like par
Recombinant chromosome
Recombinant chromosome
Parental type chromosome (looks like par
The resulting chromosomes have special names (doesn’t
everything?)
*A recombinant chromosome is one that has been broken and
recombined with another chromosome hence recombinant. Crossing
over is also known as homologous recombination – recombining
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: How are homologous chromosomes related?
Identify the sources of genetic
variability in sexually reproducing
organisms:
1. Independent orientation
2. Random fertilization
3. Crossing-Over
(not quite…)
Is that it? Are we finally finished?
4. Mutations
Mutations are changes in the DNA that can be caused by electromagnetic
radiation (light: UV, x-rays, gamma rays), mutagenic chemicals, viruses, nuclear
radiation, mistakes during replication, and others. However, such changes are
In the
only relevant to ones offspring if they occur where?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
I guess you aren’t 1 in 64
trillion possible
You are combinations…
1 in some ridiculously huge
number that I can’t calculate
possible combinations!
(The real question is, would you still be you if you were any other
combination? And how many changes in your DNA would it take for it not
to be you anymore?...)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Review Question:
A particular diploid species of annelid
has a chromosome number of 10. How
many chromosomal combinations are
possible in the gametes assuming no
crossing n
over/mutations?
=5
2n = 25 = 32
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: Describe how gametes are formed.
Review Question:
A fruit fly (Drosophila melanogaster)
somatic cell (diploid) contains 8
chromosomes. How many possible
offspring can be generated if crossing
over/mutations
n = 4 is ignored?
24 = 16 possible
16
x
16
=
256
4 = 16 possible
2
sperm
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
Nothing is perfect, including meiosis. A
number of diseases can be caused by
errors in meiosis resulting in abnormal
numbers of chromosomes.
How can one determine if a disease is caused
by or if someone has an abnormal chromosome
arrangement?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
How can one determine if a disease is caused
by or if someone has an abnormal chromosome
arrangement?
1. Isolate lymphocytes (type of white blood cell) from a
simple blood sample, or fetal cells from amniotic fluid /
placenta
2. Stimulate cell division in a tissue culture flask
3. Arrest (stop) the cell in metaphase. Why?
- Chromosomes are condensed and visible, and it is a checkpoint, which allows us
to stop it here by inhibiting internal signals.
4. Put cells on a cover slide and lyse them (break them
open with certain chemicals) and wash away cell fragments
leaving behind the chromosomes.
5. Stain the chromosomes with special dye
(Process takes about a week)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
A second method:
Fig.
8.19
1. Blood sample taken and spun in a centrifuge.
- Centrifuges can spin samples at very high speeds (10,000’s of
rpms resulting in forces as high as 100,000 times the force of
gravity)
- The more dense material ends up on the bottom (red blood
cells in this case) and less dense material on above this (white
blood cells and then fluid or plasma).
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
A second method:
2. A hypotonic solution is added to the sample, which will lyse
the red blood cells (weaker), leaving the white ones, some of
which are in prophase/metaphase swollen, but not popped.
Fig. 8.19
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
A second method:
3. A drop of the sample containing WBCs is placed on a cover
slide, dried and then stained.
Fig. 8.19
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
For both methods, the result is
a smear of condensed
chromosomes from a single
cell called a karyotype.
What is the first thing you
would do?
A digital picture is taken and
the chromosomes are first
counted. There should be
(from 46
a human cell):
Then what?
karyotyping
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
The chromosomes are paired
up and organized according
to size and banding patterns
(the dye sticks better to A-T
rich regions – segments of the
DNA with many A-T base
pairs):
Is this smear (karyotype) from
a male or a female cell?
Female, it is XX
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
Is this smear (karyotype) from
a male or a female cell?
Male, it has a Y chromosome
Analyze the karyotype:
There are 3
number 21
chromosomes.
This
is called
(tri:3, somy:body)
Trisomy 21
Down Syndrome
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
What causes Down Syndrome (Trisomy
21)?
1. First hypothesize what the chromosome combination
present in the gametes of the parents of an individual with
Down Syndrome would be.
- One gamete could have an extra chromosome 21 (two
number 21’s), while the other gamete is normal.
2. How could an extra chromosome end up in one of the
gametes?
CHROMOSOMAL NONDISJUNCTION in Meiosis II
CHROMOSOMAL NONDISJUNCTION in Meiosis II
CHROMOSOMAL NONDISJUNCTION in Meiosis II
CHROMOSOMAL NONDISJUNCTION in Meiosis I
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
Viable Autosomal nondisjunctions:
1) Trisomy 21 (Down syndrome)- most common in viable (survivable) births
2) Trisomy 18 (Edwards syndrome)
3) Trisomy 13 (Patau syndrome)
4) Trisomy 12 (A indicator of Chronic Lymphocytic Leukemia)
5) Trisomy 9
6) Trisomy 8 (Warkany syndrome 2)
Non-Viable Autosomal nondisjunctions:
Trisomy 16 - most common trisomy in humans:
- occurs in more than 1% of pregnancies.
- Usually results in spontaneous miscarriage in the first trimester.
(Do not memorize these other then trisomy 16 info and Down Syndrome)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
What about if non-disjunction occurs in
the sex chromosomes?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
Klinefelter’s Syndrome (XXY)
- Sterile male typically
- Female characteristics
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
XXXXY
Klinefelter’s
syndrome: can be
any multiple of X
with a single Y.
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
Turner Syndrome
- Shorter stature (height)
- Enlarged hands and feet
- Underdeveloped ovaries (infertile)
- Other problems (high blood pressure,
heart problems, etc…)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
(normal for the most part)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
What is the total number of
chromosomes you would expect to find
in a woman with Turner syndrome?
45, missing one X
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What happens when meiosis goes wrong?
Other mishaps can occur during meiosis
resulting in chromosomal abnormalities that may
cause disease. These abnormalities include…
1. Deletions
2. Duplications
3. Inversions
4. Translocations
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
There is a “mistake” made during meiosis resulting in
the loss of a chromosome segment.
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
Diseases caused by deletions
include:
1. Cri du chat“cry of the cat”
- Cat-like cry
- Low birth weight, cognitive (information
processing) delays, motor (movement)
and speech problems
- Chromosome 5 deletion
- Life span is normal (your book is
incorrect)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
Diseases caused by deletions
include:
2. Williams syndrome
- Deletion of 26 genes in chromosome 7
- Elf like facial appearance
- Unusually cheerful
- Unpredictable negative outbursts
- Mental retardation
- Shortened life span due to narrowed
arteries
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
Diseases caused by deletions
include:
3. Duchenne’s muscular dystrophy
i. Dystrophin gene
- Largest gene in genome
- 2.4 million base pairs!!!!!!!!!
- Takes 16 hours to transcribe
(to make a mRNA)!!!!!!!
- Protein is 3500 amino acids!
- X linked gene (means it is on the X- Function: connects muscle cell cytoskeleton to ECM (anchors
chromosome)
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
Diseases caused by deletions
include:
3. Duchenne’s muscular dystrophy
ii. Symptoms begin at 2 to 6 years old
iii. Develop muscle weakness and
eventually failure
iv. Wheelchair by age 12
v. Survival beyond 20 years old is
rare
vi. Affects 1 in 3500 MALES
Why are carrier females prevalent, but afflicted females
rare?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
Duplications can accompany deletions if the
deleted section is inserted into the homologous
chromosome during crossing over.
This can have a major role in evolution. Can you
predict why?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
The duplicated genes are now free to mutate (change)
without causing a loss of critical proteins since the original
genes are there. The genes can eventually produce
proteins that might become new tools for the cell…giving
it new functions.
**Many of our genes arose by duplication events followed by mutations
resulting in many different proteins having similar structure (divergent
evolution).
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
Above are three enzymes (proteins) that catalyze three different reactions
coded for by three different genes. Do you think those genes arose
Highly,
highly, highly
unlikely.
These three genes likely arose by gene duplication from a single
independent
of each
other?
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
Inversion results when a segment of a chromosome gets flipped or inverted.
- Less likely to be harmful compared to deletion and duplications
- All genes still present
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
Reciprocal translocations can occur between NONHOMOLOGOUS
chromosomes.
Normal if it happens in somatic cells – all genes still present.
If occurs in meiosis it can lead to Down syndrome if a piece of chromosome
21 is tranlocated onto another chromosome.
Reciprocal translocation
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
Congenital disorders
- Disorders present at birth (all the ones we have
spoken about thus far)
- Caused by genetic changes in sperm and/or ovum
or environment in uterus.
Non-Congenital disorders
- Disorders that occur or arise after birth
- Ex) cancer, heart disease, etc…
Chapter 13 - Meiosis and Sexual Life Cycles
AIM: What are some other ways chromosomes can be altered?
Cancer (non-congenital) caused by a reciprocal translocation
between chromosomes 9 and 22.
The translocation activates a cell division gene.
Chapter 13 - Meiosis and Sexual Life Cycles
Review Question
Reminder Genetic changes are ONLY passed to offspring
(inherited) if they occur…
IN THE
GAMETES