Transcript Meiosis Notes - Dr. Annette M. Parrott

Meiosis
a Dr.
Production
Watch the 3 minute video segment "Asexual
Reproducers" at
http://www.pbs.org/wgbh/evolution/library/01/5/l_0
15_01.html
Also view the 4 minute video segment "The Red
Queen" at
http://www.pbs.org/wgbh/evolution/library/01/5/l_0
15_03.html
• While viewing the videos answer the following
questions:
– What are 2 advantages and 2 disadvantages of
sexual reproduction?
– What are 2 advantages and 2 disadvantages of
asexual reproduction?
Importance of Meiosis
1. Allows conservation of
chromosome number in
sexually reproducing species
2.Allows genetic variation
• Does a 5 year old boy
have mitotic divisions
occurring?
• Does a 5 year old boy
have meiotic divisions
occurring?
• Does a 5 year old girl
have mitotic divisions
occurring?
• Does a 5 year old girl
have meiotic divisions
occurring?
Essential knowledge 3.A.2: In eukaryotes, heritable
information is passed to the next generation via
processes that include the cell cycle and mitosis or
meiosis plus fertilization.
a. The cell cycle is a complex set of stages that is highly regulated with checkpoints,
which determine the ultimate fate of the cell.
• 1. Interphase consists of three phases: growth, synthesis of DNA, preparation for
mitosis.
• 2. The cell cycle is directed by internal controls or checkpoints. Internal and
• external signals provide stop-and-go signs at the checkpoints.
– Mitosis-promoting factor (MPF)
– Action of platelet-derived growth factor (PDGF)
– Cancer results from disruptions in cell cycle control
• 3. Cyclins and cyclin-dependent kinases control the cell cycle.
• 4. Mitosis alternates with interphase in the cell cycle.
• 5. When a cell specializes, it often enters into a stage where it no longer divides, but
it can reenter the cell cycle when given appropriate cues. Nondividing cells may exit
the cell cycle; or hold at a particular stage in the cell cycle.
Essential knowledge 3.A.2: In eukaryotes, heritable
information is passed to the next generation via
processes that include the cell cycle and mitosis or
meiosis plus fertilization.
c. Meiosis, a reduction division, followed by fertilization ensures genetic diversity in
sexually reproducing organisms.
• 1. Meiosis ensures that each gamete receives one complete haploid (1n) set of
chromosomes.
• 2. During meiosis, homologous chromosomes are paired, with one homologue
originating from the maternal parent and the other from the paternal parent.
Orientation of the chromosome pairs is random with respect to the cell poles.
• 3. Separation of the homologous chromosomes ensures that each gamete receives a
haploid (1n) set of chromosomes composed of both maternal and paternal
chromosomes.
• 4. During meiosis, homologous chromatids exchange genetic material via a process
called “crossing over,” which increases genetic variation in the resultant gametes. 5.
Fertilization involves the fusion of two gametes, increases genetic variation in
populations by providing for new combinations of genetic information in the zygote,
and restores the diploid number of chromosomes.
Essential knowledge 3.A.2: In eukaryotes, heritable
information is passed to the next generation via
processes that include the cell cycle and mitosis or
meiosis plus fertilization.
LO 3.7 The student can make predictions about natural phenomena occurring during
the cell cycle.
LO 3.8 The student can describe the events that occur in the cell cycle.
LO 3.9 The student is able to construct an explanation, using visual representations or
narratives, as to how DNA in chromosomes is transmitted to the next generation via
mitosis, or meiosis followed by fertilization.
LO 3.10 The student is able to represent the connection between meiosis and increased
genetic diversity necessary for evolution.
LO 3.11 The student is able to evaluate evidence provided by data sets to support the
claim that heritable information is passed from one generation to another generation
through mitosis, or meiosis followed by fertilization.
Essential knowledge 3.A.3: The chromosomal basis of
inheritance provides an understanding of the pattern of
passage (transmission) of genes from parent to offspring.
a. Rules of probability can be applied to analyze passage of single gene traits from
parent to offspring.
b. Segregation and independent assortment of chromosomes result in genetic variation.
• 1. Segregation and independent assortment can be applied to genes that are on
different chromosomes.
• 2. Genes that are adjacent and close to each other on the same chromosome tend to
move as a unit; the probability that they will segregate as a unit is a function of the
distance between them.
• 3. The pattern of inheritance (monohybrid, dihybrid, sex-linked, and genes linked on
the same homologous chromosome) can often be predicted from data that gives the
parent genotype/phenotype and/or the offspring phenotypes/genotypes.
Essential knowledge 3.A.3: The chromosomal basis of
inheritance provides an understanding of the pattern of
passage (transmission) of genes from parent to offspring.
c. Certain human genetic disorders can be attributed to the inheritance of single gene
traits or specific chromosomal changes, such as nondisjunction.
–
–
–
–
–
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• Sickle cell anemia
• Tay-Sachs disease
• Huntington’s disease
• X-linked color blindness
• Trisomy 21/Down syndrome
• Klinefelter’s syndrome
d. Many ethical, social and medical issues surround human genetic disorders.
– • Reproduction issues
– • Civic issues such as ownership of genetic information, privacy, historical contexts, etc.
LO 3.12 The student is able to construct a representation that connects the process of
meiosis to the passage of traits from parent to offspring.
LO 3.13 The student is able to pose questions about ethical, social or medical issues
surrounding human genetic disorders.
LO 3.14 The student is able to apply mathematical routines to determine Mendelian
patterns of inheritance provided by data sets.
• Meiosis is also called gametogenesis and sporogenesis
Meiosis I
• Is a reduction division
X
• Prophase I
leptotene "thin-thread“, appearance of chromosomes
zygotene "yolk-thread“, homologues pr side by side & gene
by gene = synapsis, forming bivalent pairs or
tetrads
pachytene "thick-thread“, shortening & thickening of
bivalents, crossing over/recombination at
synaptonemal complex
diplotene "double-thread“, separation of homologues
chiasmata: physical evidence
diakinesis shortening chromosomes, disintegration of
envelope
Crossing Over
When homologous chromosomes, swap genetic information
Natural Mutation that allows for genetic variety
• Metaphase Ibivalents migrate to equator
• Anaphase Ihomologous chromosomes migrate to
poles not sister chromatids
• Telophase I
• (interkinesis)
Meiosis II
• Is an equational
division
• Metaphase IIcentromeres attached to spindle fibers
• Anaphase IImigration of daughter chromosomes
(formerly chromatids)
Metaphase sister
chromatids
separate
Metaphase I homologous
chromosomes separate
Metaphase II
sister chromatids
separate
Meiosis
Animation
Gametogenesis
Mitosis
Meiosis
1 division2 cells
2 divisions 4 cells
Daughter cells genetically
identical to parent cell & to
each other
Division is equational
2n2n
Sister chromatids migrate
Occurs in somatic/body cells
to reproduce body cells
Diploid diploid cells
Daughter cells are genetically
distinct from parent & each
other
1st division reduction 2n n
2nd division equational n n
Homologous chromosomes &
sister chromatids migrate
Occurs in sex cells produces
gametes
Diploid haploid
No genetic variation
Crossing over in tetrads
Mitosis/Meiosis Comparison
46
46
23
46
46
23
23
23 23
23
karyotype
Nondisjunction
Junction place where things are
connected, homologous
chromosomes in meiosis I and sister
chromatids in meiosis II
Disjunction separation of junction
during anaphase I and anaphase II
Non-disjunction failure of
chromosomes to properly separate
during anaphase I and anaphase II
Nondisjunction results in
aneuploidy, or abnormal number of
copies of chromosomes
Nondisjunction/Aneuploidy
• Polyploidy 3 or more
sets of chromosomes,
(more often in plants)
• can detect before birth w/
amniocentesis
or
chorionic villi sampling
• most children w/chromo
abnormalities aborted b/4
mother realizes she's
pregnant
• incidents of aneuploidy
inc 50x w/ mothers >45
yrs
Down’s Syndrome Statistics
• The estimated incidence of Down
syndrome is between 1 in 1,000 live
births.
• In 1866, Down described clinical
characteristics of the syndrome that now
bears his name. In 1959, Lejeune and
Jacobs et al independently determined
that Down syndrome is caused by
trisomy 21. Down syndrome is by far
the most common and best known
chromosome disorder in humans.
Mental retardation, dysmorphic facial
features, and other distinctive
phenotypic traits characterize the
syndrome.
Down’s Syndrome Karyotype
trisomy 21
Down’s Syndrome Symptoms
• eyes often slant upwards and
outwards, and the back of the
head may be unusually flat.
• as high as 40% of Down's babies
will have some sort of congenital
heart defect
• will have some level of learning
disorder
• immune system which makes
them prone to infections,
particularly chest and sinus
infections.
• can have problems regulating
their temperature, and can have
very dry skin.
• 1. 60 to 80% of people with Down syndrome will have hearing
deficits.
• 2. 40-45% of children with Down syndrome will have congenital
heart disease.
• 3. Intestinal abnormalities also occur at a higher frequency and
may need to be surgically corrected at birth.
• 4. People with Down syndrome may have more eye problems.
• 5. Obesity is often noted during adolescence and early
adulthood.
• 6. 15-20% of people with Down syndrome will have thyroid
problems.
• 7. Skeletal problems like kneecap subluxation, hip dislocation,
and atlantoaxial instability (the first two neck bones are not well
aligned because of the presence of loose ligaments) are more
common.
• 8. Other important medical problems should be addressed as well
including: leukemia, Alzheimer's disease, immune system
concerns, seizure disorders, sleep apnea, and skin disorders.
Patau’s Syndrome Statistics
• Incidence of Patau syndrome
is approximately 1 per 8,00012,000 live births.
• Patau syndrome is the least
common and the most severe
of the viable autosomal
trisomies. Median survival is
fewer than 3 days. First
identified as a cytogenetic
syndrome in 1960, Patau
syndrome is caused by an
extra copy of chromosome 13,
Patau’s karyotype
trisomy 13
Cleft palate
Polydactyly
cyclopia (single
eye) with a
proboscis (the
projecting tissue
just above the
eye).
Edward’s Syndrome Statistics
• Prevalence is
approximately 1 in 60008000 live births.
• Trisomy 18 was
independently described
by Edwards et al and
Smith et al in 1960.
Among liveborn children,
trisomy 18 is the second
most common autosomal
trisomy after trisomy 21.
Edward’s Syndrome
Trisomy 18
Edward’s Syndrome Symptoms
• Approximately 95% of conceptions with trisomy
18 die in embryonic or fetal life; 5-10% of
affected children survive beyond the first year.
• The high mortality rate is usually due to the
presence of cardiac and renal malformations,
feeding difficulties, sepsis, and apnea caused by
CNS defects.
• Severe psychomotor and growth retardation are
invariably present for those who survive beyond
infancy.
overlapping digits with
the second and fifth fingers
overriding the third and fourth
fingers respectively
Microglassia, microcephaly and
other head abnormalities
Turner’s Syndrome Statistics
• In 1938, Henry Turner first
described Turner syndrome,
which is one of the most
common chromosomal
abnormalities. More than 95%
of adult women with Turner
syndrome exhibit short stature
and infertility.
• Frequency is approximately 1
in 2,000 live-born female
infants. As many as 15% of
spontaneous abortions have a
45 X karyotype.
Turner’s Syndrome Karyotype
monosomy 23
Turner’s Syndrome Symptoms
• Webbed neck
• Exhibit female
phenotype; sterile
• Short stature, high
arched palate
Klinefelter’s Syndrome Statistics
• Approximately 1 in 500-1,000 males is born
with an extra sex chromosome; over 3,000
affected males are born yearly. The
prevalence is 5-20 times higher in the
mentally retarded than in the general
newborn population.
• In 1942, Klinefelter et al published a report
on 9 men who had enlarged breasts, sparse
facial and body hair, small testes, and
inability to produce sperm. In 1959, these
men with Klinefelter syndrome were
discovered to have an extra sex chromosome
(genotype XXY) instead of the usual male
sex complement (genotype XY).
Klinefelter’s Syndrome Karyotype
Trisomy 23
Klinefelter’s Syndrome Symptoms
• fetal development is that of a
normal male. However, as the
child grows and approaches
puberty, he experiences
excessive gynecomastia, with
low serum testosterone levels.
Infertility is common, and
general appearance is tall and
thin.
• A higher than normally
expected percentage of these
individuals have been reported
to have emotional disorders
Extra Y Statistics
• Most males have the 46-XY karyotype, but about 1 guy
in 1000 has two Y chromosomes, and is an XYY
("diplo-Y", "diplo Y", "YY", "polysomy Y").
• XYY's average substantially taller, tend to be wirybuilt, and tend to have severe acne. Minor birth defects
-- like pectus, crooked eye, and minor outturning of the
elbows, are supposed to be common in XYY's.
• Now, XYY boys usually do have serious behavioral and
cognitive problems. The extra "Y" in an XYY is
obviously not silent (as is the extra "X" in a XXX
woman). It seems likely that the second "Y" adds a bit
more aggressiveness to a man's overall personality.
Extra Y Karyotype
trisomy/quadrasomy 23
Meta Female Statistics
•
•
With 3 X chromosomes (XXX), these females usually have no
apparent physical abnormalities except tallness and menstrual
irregularities
As adults, these individuals are usually an inch or so taller
than average with unusually long legs and slender
torsos. They have normal development of sexual
characteristics and are fertile. They may have slight learning
difficulties and are usually in the low range of normal
intelligence. They tend to be emotionally immature for their
size during childhood. None of these traits prevent them from
being socially accepted as ordinary women. This type of
chromosomal abnormality is apparently rare and little is
known about it. However, the frequency is approximately 1 in
1,000 female infants and it may be more common when the
mother is older. Metafemales are also called "triple-X
females."
Meta Female karyotype
Trisomy 23
Cri-du-Chat Statistics
• The estimated incidence is about 1 in
50,000 livebirths
• In 1963, Lejeune et al described a
syndrome of multiple congenital
anomalies, mental retardation,
microcephaly, abnormal face, and a
mewing cry in infants
• Cri-du-chat syndrome is an autosomal
deletion syndrome caused by a partial
deletion of chromosome 5p. It is
characterized by distinctive, highpitched, catlike cry in infancy with
growth failure, microcephaly, facial
abnormalities, and mental retardation
throughout life.
Cri-du-Chat Karyotype
Cri-du-chat Symptoms
• Approximately 75% of the patients
with cri-du-chat syndrome die within
the first few months of life and about
90% before they are aged 1 year. These
figures are from an older study (1978),
and decreased morbidity and mortality
are most likely with contemporary
interventions. Survival to adulthood is
possible.
• Pneumonia, aspiration pneumonia,
congenital heart defects, and
respiratory distress syndrome are the
most common causes of death.
Polyploidy in plants
• common in plants, especially
in30%-70% angiosperms, are
thought to be polyploid.
• i.e. Species of coffee plant
with 22, 44, 66, and 88
chromosomes suggesting
ancestral condition (n) = 11
and a (2n) = 22, from which
evolved the different
polyploid descendants.
• Polyploid plants are larger,
leading to created varieties
of watermelons, marigolds,
and snapdragons
•
Plant
Probable
ancestral
haploid
number
Chromo
#
Ploidy
level
domestic oat
7
42
6n
peanut
10
40
4n
sugar cane
10
80
8n
banana
11
22, 33
2n, 3n
white potato
12
48
4n
tobacco
12
48
4n
cotton
13
52
4n
apple
17
34, 51
2n, 3n
Origin of Polyploidy
• Accident Doubling Plants, (vs
animals), form germ cells from
somatic tissues. If the chromosome
content of a precursor somatic cell
has accidentally doubled (e.g., as a
result of passing through S phase of
the cell cycle without following up
with mitosis and cytokinesis), then
gametes containing 2n chromosomes
are formed.
• Naturally occuring As the
endosperm (3n) develops in corn
(maize) kernels (Zea mays), its cells
undergo successive rounds (as many as
5) of endoreplication producing nuclei
that range as high as 96n.
• When rhizobia infect the roots of
their legume host, they induce the
infected cells to undergo
endoreplication producing cells that
can become 128n (from 6 rounds of
endoreplication).
Polyploidy and Speciation
• When a newly-arisen tetraploid
(4n) plant tries to breed with
its ancestral species (a
backcross), triploid offspring
are formed. These are sterile
because they cannot form
gametes with a balanced
assortment of chromosomes.
• However, the tetraploid plants
can breed with each other. So
in one generation, a new species
has been formed.
Alternation of Generations
Fungi Life Cycle
References
• Nondisjunction Animation:
http://www.people.virginia.edu/~rjh9u/ndjanim.html
• Patau’s Syndrome:
http://medgen.genetics.utah.edu/photographs/pages/trisomy_13.htm
• Turner’s Syndrome: http://author.emedicine.com/PED/topic2330.htm
• Klinefeleter’s Syndrome: http://author.emedicine.com/ped/topic1252.htm
• Cri-du-chat Syndrome: http://author.emedicine.com/ped/topic504.htm
• Edward’s Syndrome: http://author.emedicine.com/ped/topic652.htm
• XYY: http://www.pathguy.com/xyy.htm
• Metafemales: http://www.aaa.dk/TURNER/ENGELSK/TRIPLEX.HTM