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45 Cards in this Set
- Front
- Back
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What is aneuploidy?
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An abnormal number of chromosomes
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What are the 3 most common autosomal aneuploidies?
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-Trisomy 21 (Down)
-Trisomy 18 (Edward) -Trisomy 13 (Patau) |
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Why don't we ever see autosomal deletions, only duplications?
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Because you can't survive without one of your autosomes.
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What are 3 types of down syndrome?
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-Free trisomy 21
-Translocation Down's syndrome -Partial trisomy (mosaic) |
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What is the cause of 95% of downs syndrome cases?
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Maternal nondisjunction
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What are the 4 common physical features of DS patients?
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-mongoloid (epicanthic folds)
-flat occiput -short broad hands -large tongue - macroglossia |
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What congenital defects are DS patients apt to have?
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-Cardiac (ASD/VSD, AV canal defects)
-Duodenal atresia |
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What are 2 diseases that patients with DS often develop?
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-Leukemia
-Alzheimer's disease |
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What is the incidence of Down's syndrome in the general population?
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1/700
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What is the incidence of DS in parents that already have 1 child with it?
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1/100 (a 1% increase)
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What is 4% of DS cases?
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Translocation trisomy 21
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What occurs in translocation trisomy 21?
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Attachment of 21 to the short arm of a chromosome (13,14,15, 21, or 22), so there is a normal number of chromosomes but 3 copies of 21
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What is the chromosome number in the parent that carries the translocation?
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45
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What sex is more predisposed to being a translocation carrier?
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Females
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What is 1% of Down syndrome?
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Mosaicism
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What causes DS mosaicism?
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Mitotic nondisjunction
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What is mosaicism?
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A mixture of cells in patients
-some have normal chromosomes -some have trisomy 21 |
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When does DS mosaicism develop?
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Early in embryonic development
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How do Trisomy 13 and 18 compare to 21?
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Much more severe, low long term survival rate.
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What are the features of Trisomy 13?
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-Cleft lip/palate
-Holoprosencephaly -Prominent calcaneus -Polydactyly |
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What are the features of Edwards syndrome (trisomy 18)?
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-Micrognathia
-overlapping digits -Profound developmental delay -Severe heart defects |
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What is the incidence of
-Patau syndrome -Edward syndrome |
Patau - 13 - 1/15000
Edward - 18 - 1/8000 |
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What is the smallest cytogenetically visible fragment of DNA?
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3 to 5 million base pairs - ONE BAND
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How many genes are on average contained in one band?
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30
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How many extra genes are conferred in trisomy 21?
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>450
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What is the chromosome abnormality in Turners syndrome?
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45X
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What are the common physical features of 45x turner syndrome?
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-Short stature (4'10")
-Broad webbed neck -Absence of menarche -Sterility |
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Why is there a broad webbed neck?
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Due to edema in utero
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Why are girls with Turner syndrome sterile?
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Because their oocytes involute prior to birth
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What is the cause of 75% of turner syndrome?
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Loss of the PATERNAL sex chromosome
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What is the incidence of Turner syndrome in live births?
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1/2000
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What happens to the VAST MAJORITY (99%) of babies with 45X?
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They are lost before term
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So is 45X very compatible with life?
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no
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What are the intellectual capacities of girls with Turner syndrome?
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Normal - not retarded, but may have spacial perception deficits.
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What is the chromosomal abnormality in Klinefelters syndrome?
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47XXY
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What are the features of Klinefelters syndrome?
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-Tall feminized features
-Low androgens -Small testes -Fat distribution is abnormal -Gynecomastia |
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What is the incidence of Klinefelter's?
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1/700
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What is the IQ of Klinefelters syndrome patients?
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Normal
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Can males with Klinefelters have children, if they're infertile?
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Yes; there are SOME cells with normal karyotypes - in islands in the testes.
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How can a person survive with only one X chromosome?
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All people have an inactivated X chromosome anyway.
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Then why are patients with Turners and Klinefelters phenotypically different?
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Because there are SOME X chromosomes that escape inactivation in normal people.
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So what happens as the number of extra X chromosomes increases?
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Developmental delay increases in severity
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What does an extra Y chromosome do?
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-Makes you tall
-Gives you large canines -Makes you fertile -Makes you go to prison bc you're mentally subnormal |
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What is the karyotype of most males with an extra Y?
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47 XYY
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What is the incidence of 47 XYY?
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1/700
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