abnormal meiosis. nondisjunction happens when two homologus chromosomes don’t separate during...
Post on 24-Dec-2015
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Abnormal meiosis
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
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.
Trisomy Monosomy
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)
Down’s Syndrome
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
Female with a tendency toward male traits
May be sterile (can be fertile) May be mentally challenged but may
also have normal intelligence
XXY Male Sterile, underdeveloped sexually Thin, high pitched voice May be mentally challenged
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”.
Because the Y chromosome is shorter than the X chromosome, YO babies are miscarried and never born.
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