abnormal meiosis. nondisjunction happens when two homologus chromosomes don’t separate during...
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Abnormal meiosis
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Nondisjunction happens when two homologus chromosomes don’t separate during meiosis
One pole ends up with an extra chromosome and one pole ends up missing a chromosome
The abnormal separation of the tetrads causes resulting gametes to have one too many or one too few chromosomes
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Monosomy Trisomy
The resulting gamete in humans has only 22 chromosomes
After fertilization, the individual will have only 45 chromosomes instead of 46.
The resulting gamete has an extra chromosome – so 24 .
After fertilization, the individual will have 47 chromosomes.
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Trisomy Monosomy
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Abnormal foot and palm crease Also known as trisomy 21 – extra
#21 chromosome is the most common cause
Increases with the age of the mother Enlarged tongue, weak muscle tone Slanted eyes Occurs in 1/600 births (under 35 –
1/1000 – over 45 1/60)
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Down’s Syndrome
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Turner’s Syndrome – also called Monosomy X - XO Female, sterile, don’t mature sexually, short
stature, thick ,wide neck, About 1 in every 300o babies are born with
Turner’s Most Turner’s fetuses are miscarried by week
20 Only develop secondary sexual
characteristics if given HRT
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Female with a tendency toward male traits
May be sterile (can be fertile) May be mentally challenged but may
also have normal intelligence
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XXY Male Sterile, underdeveloped sexually Thin, high pitched voice May be mentally challenged
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Occurs in about 1 in 1000 newborn boys
5-10 boys are born in the US every day with this disorder
Ed’s story Why it is called the “criminal
chromosome”.
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Because the Y chromosome is shorter than the X chromosome, YO babies are miscarried and never born.
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