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10 Cards in this Set
- Front
- Back
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What are the targets for FISH?
What can it be used to identify? How quickly can you get FISH results back? |
- Metaphase cells (Dividing)
- Interphase cells (non-dividing) cultured preps contain both types identify numerical abnormalities and to characterize structural rearrangements w/i 24 hours on easy to analyze samples. |
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Can down syndrome be the result of an unbalanced translocation?
What are the limitations of FISH for detecting DiGeorge syndrome? (2) |
yes.
1) can only detect v. large deletions that alter hybridization. 2) some DiGeorge microdeletions are positioned outside of the critical region that is targeted by FISH. |
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What are microdeletion syndromes?
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characterized by small (often submicroscopic) recurring interstitial deletions each of which is associated w/ specific phenotype.
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Prominent nose w/ squared nasal root, small eyes, small ears w/ abnormal folding. Abnormal palate (~70%). Congential Ht Dz (~75%). Learning defecits in almost all (75-90%). 40-50% have hypocalcemia. Immune deficiency. Psychiatric dz.
Think what? |
DiGeorge or Velocardiofacial syndrome.
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How often can you see the DiGeorge syndrome deletion on normal karyotyping?
- what do you do instead? - are most cases of DiGeorge denovo? - do we recommend parental karyotyping post DiGeorge dx? |
~25%
- FISH - yes, 94% - no, follow up w/ FISH. |
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What is the downside of G-banding? (aka?)
FISH? What new technique is helping to combine the stregnths of both? - how does it work? |
Karyotyping
- resolution is typically limited to 3-5 Mb. High resolution, but requires a clinically directed search, and the search is very specific. Microarray CGH - arrayed DNA probes provide a locus-by-locus measurement of DNA copy # variation @ many loci simultaneously. - green labeled pt DNA and red-labeled control DNA are added to wells containing array DNA sequences that contain clone of DNA sequence --> oranger = equal hybridization; green = pt DNA out-competes control; red = control outcompetes pt. |
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Does Microarray CGH coverage vary?
- What is a true loss vs a relative loss? - how can we confirm? |
yes, varies with the selection and # of clones you use.
- true loss = monosomy; relative loss = loss relative to the control (more likely to be clinically benign) - FISH |
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What type of FISH is required to differentiate between normal chromosomes and a balanced rearrangement?
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Metaphase FISH (dividing cells... chromosomes in lines w/ centromeres)
Interphase just shows us dots w/o a good understanding of where they are placed. |
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Because Array CGH tech identifies net gains and losses w/i the population, what types of things aren't identified? (2)
- can Array CGH identify the mechanism of excess/deleted material? How about the origin of it? |
1) Balanced rearrangements: remember in the example in lecture we could identify the unbalanced rearrangement in the proband, but had to do metaphase FISH to see the mother's balanced rearrangement.
2)low lvls of mosaicism/heterogeneity - no, req. Metaphase FISH and G-banded; yes, it can identify the origin. |
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Because of our limited knowledge regarding the genome, it is often difficult to distinguish between clinically relevant and benign copy number changes w/ Array CGH. what are some factors that suggest clinically benign finding?
- significant? What is currently considered the gold standard of numerical and structural abnormality dx? |
small change, no presence of genes, no apparent correlation w/ pt. phenotype, located in placenta or testes, relative loss/gain (no duplication or deletion), no dosage sensitivity of genes, inherited from clinically normal parent.
- many genes present, correlates w/ pt. phenogype, CNS & major orangs, duplication/deletion, dosage sensitive and it's a new mutation in the proband. G-band (karyotyping) |
