MMG - Lecture 18
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What is the p arm of the chromosome?
What is the q arm of the chromosome?
What is a karyotype?
Condensed chromosomes visual by microscope consisting of sister chromatids held tightly together which appear as a single entity.
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
What is an idiogram?
Diagrammatic representation of a karyotype with banding patterns.
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.
What are the acrocentric chromosomes?
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
What is the benefit of less viewing less condensed chromosomes?
- More bands are visible (more banding means more accuracy).
- Resolution depends on condensation.
What type of chromosomal abnormalities can be seen in high resolution karyotypes?
Large abnormality (>5 mb).
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.
What are the phenotypic consequences of balanced rearrangements?
Generally none b/c all genetic material is still there.
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.
When are the phenotypic consequences in balanced rearrangements?
- If rearrangements interrupts and important gene found at a break point.
- Occurs 6% of the time.
What is an unbalance rearrangement?
Deletions, duplications, isochromosomes, unbalanced reciprocal/Robertsonian translocations where genetic material is lost or gained.
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.
What is aneuploidy?
- Gain or loss of an entire chormosome (Trisomy 21, Turner)
- Can be seen on Karyotype
What is chromosomal mosaicism?
- Form of somatic mosaicism.
- The presence of two or more different chromosome complements in an individual.
What type of rearrangements can be seen on a Karyotype?
- Chromosomal Mosaicism
- Supernumerary Chromosomes
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).
What is the effect on a child who has a parent with balanced rearrangements?
Predisposes child to unbalanced rearrangements.
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