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What is the p arm of the chromosome?
Short arm.
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What is the q arm of the chromosome?
Long arm.
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What is a karyotype?
Condensed chromosomes visual by microscope consisting of sister chromatids held tightly together which appear as a single entity.
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What is the karyotype for:
- normal female
- normal male
- male with Down syndrome
- female with Turner syndrome
- 46, XX
- 46, XY
- 47, XX, +21
- 45, X
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What is an idiogram?
Diagrammatic representation of a karyotype with banding patterns.
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What is an acrocentric chromosome?
- Chromosome where the p arm is a stalk of satellite DNA which contains repetitive copies of ribosomal RNA genes.
- Involved in Robertsonian Translocations.
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What are the acrocentric chromosomes?
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In Giemsa banding (G-banding) what are the light and dark bands?
- Dark Bands: A-T rich, gene poor
- Light Bands: G-C rich, gene rich
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What is the benefit of less viewing less condensed chromosomes?
- More bands are visible (more banding means more accuracy).
- Resolution depends on condensation.
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What type of chromosomal abnormalities can be seen in high resolution karyotypes?
Large abnormality (>5 mb).
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What is a balanced rearrangement?
Inversions, insertions and balanced reciprocal and Robertsonian translocations that simple rearrange the genetic material, but still leave it all intact.
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What are the phenotypic consequences of balanced rearrangements?
Generally none b/c all genetic material is still there.
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Can balanced rearrangements be seen on Karyotypes?
Generally yes, but some may need to be detected by CGH or FISH if rearrangement was small and only visible on molecular level.
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When are the phenotypic consequences in balanced rearrangements?
- If rearrangements interrupts and important gene found at a break point.
- Occurs 6% of the time.
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What is an unbalance rearrangement?
Deletions, duplications, isochromosomes, unbalanced reciprocal/Robertsonian translocations where genetic material is lost or gained.
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What are the phenotypic consequences of unbalanced rearrangements?
- This happens often, especially when visible on karyotype (due to large deletion).
- Smaller rearrangements seen by FISH or CGH may or may not be associated with phenotypic consequences.
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What is aneuploidy?
- Gain or loss of an entire chormosome (Trisomy 21, Turner)
- Can be seen on Karyotype
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What is chromosomal mosaicism?
- Form of somatic mosaicism.
- The presence of two or more different chromosome complements in an individual.
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What type of rearrangements can be seen on a Karyotype?
- Balanced
- Unbalanced
- Aneuploidy
- Chromosomal Mosaicism
- Supernumerary Chromosomes
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What are Supernumerary Chromosomes?
- Rings and Markers (extra "bits" of chromosomes which may or may not include genes).
- Rings - deletion on either end of chromosome leading to sticky ends that reattach.
- Markers may or may not contain genetic material (prognosis hard to predict).
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What is the effect on a child who has a parent with balanced rearrangements?
Predisposes child to unbalanced rearrangements.
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