Transcript Cell Division - Science-with

Cell Division
Meiosis
Cell Division
Meiosis
Abnormal
Meiosis
Cell Division
Meiosis
Abnormal Meiosis
 nondisjunction occurs when two homologous chromosomes
fail to separate during meiosis or mitosis.
 one of the daughter cells will have too many chromosomes,
while another will have too few.
 the effects of nondisjunction are more devastating in the
production of gametes.
 nondisjunction occurs during anaphase I or anaphase II
Cell Division
Meiosis
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nondisjunction in humans produces:
 gametes with 22 and 24 chromosomes.
 if the gamete with 24 chromosomes joins with a normal
gamete of 23 chromosomes a zygote containing 47
chromosomes is produced.
 the zygote will have three chromosomes rather than a
pair.
 this condition is referred to as trisomy.
Cell Division
Meiosis
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if the gamete with 22 chromosomes joins with a normal
gamete of 23 chromosomes a zygote containing 45
chromosomes is produced.
 the zygote will have one chromosome rather than a pair
 this condition is referred to as monosomy.
once the cells of trisomic or monosomic zygotes begin to
divide, each cell of body will be one plus or one minus a
chromosome.
Cell Division
Meiosis
Cell Division
Meiosis
Nondisjunction Disorders
 Male and Female Syndromes
 Down Syndrome
 trisomy 21
 Patau Syndrome
 trisomy 13
 Edward Syndrome
 trisomy 18
E) Abnormal Meiosis
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Down’s Syndrome
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cause: trisomy of the 21st chromosome
symptoms:
 mental retardation,
 a round full face, enlarged tongue, large forehead
 short stature
 shortened lifespan
 higher risk of other medical conditions, such as heart
defects(50%), leukemia(10-50 times more common),
Alzheimer’s, etc
prevalence:
 the most common non-lethal non-disjunction disorder
 affects about 1 in 800 babies (risk increases significantly
with age of mother)
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Patau Syndrome
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 cause: trisomy of the 13 chromosome
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symptoms:
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least common and most severe of the autosomal trisomies
extreme facial deformation (e.g. cyclopia, missing nose)
polydactyly
long term neurological disability,
heart defects, frequent pneumonia and other respiratory
infections.
prevalence: about 1 in 10,000 live births
prognosis:
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very poor, most embryos do not survive gestation and are
spontaneously aborted
of those surviving to term gestation, approximately 82-85% do
not survive past 1 month of age, and 85-90% do not survive past
1 year of age (there have only been 5 cases reported in the
medical history of patients living beyond 10 years of age)
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Edwards Syndrome
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 cause: trisomy of the 18 chromosome
 symptoms:
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prevalence:
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low birth weight;
a small, abnormally shaped head; small jaw;
small mouth; low-set ears;
clenched fists with overlapping fingers.
breathing or heart defects normally associated
with premature babies
1:3000 live births
second most common autosomal trisomy
increased risk as a woman's age increases
prognosis:
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very poor - about half die in utero
of liveborn infants, only 50% live to 2 months, and
only 5 - 10% will survive their first year of life.
Median life span is 5-15 days.
medical interventions for related medical problems
(e.g. heart defects) usually withheld due to poor
prognosis
Cell Division
III) Meiosis
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Gender Specific
 Turner Syndrome (female)
 X0
 Triplo-X Syndrome (female)
 XXX or XXXX
 Klinefelter Syndrome (male)
 XXY or XXXY
 Jacob’s Syndrome (male)
 XYY
E) Abnormal Meiosis
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Turner’s Syndrome
 cause: sex chromosomes undergo non-disjunction, causes a
monosomic female
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symptoms: (females only)
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female only has one X chromosome instead of the normal two
it is the only known viable monosomy in humans
does not occur in males because the embryo cannot survive
without at least one X chromosome
(females born as XXX are healthy and cannot be distinguished
from normal XX females except by karyotype)
sexually underdeveloped,
tend to be short and have thick, widened necks
sterility, congenital heart disease and hypothyroidism
prevalence:
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1 in 5,000 births
most Turner’s embryos resulting in miscarriages
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Klinefelter Syndrome
 cause: again, a non-disjunction of
the sex chromosomes, but this time
producing a trisomy
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symptoms: (males)
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at birth, the child will have primary male
sex characteristics and will appear male
at puberty, he will begin producing high
levels of female sex hormones (e.g.
estrogen)
(males with an extra Y chromosome used
to be thought of as destined to be
criminals; now we know them typically to
be only taller than average)
though he has male sex organs, they are
small and the man is sterile
he will have breast enlargement and other
female body characteristics
X-linked recessive conditions occur less
frequently than in normal males
prevalence: 1 in 1000 births
Cell Division
Meiosis
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the chances of nondisjunction disorder increases with age
 chances of having a child with Down’s Syndrome
 conceiving between 20 and 24 years, 1 in 1490
 conceiving at age 40, 1 in 106
 conceiving at age 49, 1 in 11
E) Abnormal Meiosis
Cell Division
Meiosis
Cell Division
Meiosis
Cell Division
Meiosis
Karyotypes
Cell Division
Meiosis- Recall
Karyotype
 a chart of chromosomes.
 obtained by mixing a small sample of tissue with a chemical that
stimulates mitotic division.
 division is the stopped during metaphase.
 chromosomes are stained
 a picture is taken and chromosomes are paired up with their
homologue.
 homologue chromosomes are similar in size, length,
centromere location and banding pattern.
 they are organized in decreasing size with the sex
chromosome placed at the end.
Cell Division
Meiosis
Cell Division
Meiosis
Normal Male
E) Karyotype
Cell Division
Meiosis
Jacobs Syndrome
Cell Division
Meiosis
Turner Syndrome
Cell Division
Meiosis
Down Syndrome