cell division meiosis cell division meiosis abnormal meiosis
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Cell DivisionMeiosisAbnormal 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 DivisionMeiosis 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 DivisionMeiosis
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 DivisionMeiosisNondisjunction Disorders Male and Female Syndromes
Down Syndrome trisomy 21
Patau Syndrome trisomy 13
Edward Syndrome trisomy 18
E) Abnormal Meiosis
Down’s Syndrome 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)
Patau Syndrome cause: trisomy of the 13th chromosome
least common and most severe of the autosomal trisomies
symptoms: 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:
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)
Edwards Syndrome cause: trisomy of the 18th chromosome symptoms:
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 prevalence:
1:3000 live births second most common autosomal trisomy increased risk as a woman's age increases
prognosis: 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 DivisionIII) Meiosis 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
Turner’s Syndrome cause: sex chromosomes undergo non-disjunction,
causes a monosomic female 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)
symptoms: (females only) sexually underdeveloped, tend to be short and have thick, widened necks sterility, congenital heart disease and hypothyroidism
prevalence: 1 in 5,000 births most Turner’s embryos resulting in miscarriages
Klinefelter Syndrome cause: again, a non-disjunction of
the sex chromosomes, but this time producing a trisomy 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)
symptoms: (males) 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 DivisionMeiosis 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 DivisionMeiosis- RecallKaryotype 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.
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