errors in meiosis. non-disjunction is the failure of homologous chromosomes, or sister chromatids,...
TRANSCRIPT
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Errors in Meiosis
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Non-disjunction is the failure of homologous chromosomes, or sister chromatids, to separate during meiosis.
• Nondisjunction may occur during meiosis 1 or meiosis 2
• Abnormal number of chromosomes may result
Non-disjunction is one of the Two major Non-disjunction is one of the Two major occurrences of Meiosisoccurrences of Meiosis
(The other is Crossing Over)(The other is Crossing Over)
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Non-disjunction results in the production of zygotes with abnormal chromosome numbers
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An abnormal chromosome number (abnormal amount of DNA) is damaging to the offspring.
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• Should the gamete with the chromosome pair be fertilized then the offspring may or may not develop properly or at all
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• If it occurs in one of the smaller genes…
• 13, 15, 18, 21, 22
• There is some chance of viability
• Trisomy 21 and 22 may survive into adulthood
• If it occurs in one of the larger genes…
• There is a failure in early development and termination occurs
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Monosomy • If an organism
has Monosomy 23 it has only one chromosome in the 23rd set.
Usually occurs in one of two ways
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Trisomy• If an organism
has Trisomy 21, there are three chromosomes in the 21st set.
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Genetic TestingGenetic Testing Amniocentesis
Physician removes amniotic fluid from around the fetus. Cells are cultured for karyotype
Chorionic villus sampling Narrow tube
inserted through the cervix to suction out a sample of the placenta (fetal cells)
Immediate karyotype
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Down’s Syndrome – Trisomy 21
Turner’s Syndrome – Monosomy 23 (X)
Kleinfelter’s Syndrome – Trisomy 23 (XXY)
Edward’s Syndrome – Trisomy 18
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Fertile Normal physically Normal mentally Increase in
testosterone Perhaps more
aggressive Normal lifespan 1 in 1,800 births
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Scarce beard Longer fingers and
arms Sterile Delicate skin Low mental ability Normal lifespan 1 in 1,100 births
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• Short, broad hands
• Stubby fingers• Rough skin• Impotency in
males• Mentally retarded• Small round face• Protruding tongue• Short lifespan• 1 in 1,250 births
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1 in 4400 births• XX=80%• XY=20%
Small head Mentally retarded Internal organ
abnormalities 90% die before
5 months of age
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1 in 4400 births 96-98% do not survive to
birth No menstruation No breast development Small hips Broad shoulders and neck Other health issues can
include heart disease, horseshoe shaped kidneys, learning disabilities
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