Structural Chromosomal Abnormalities Flashcards
What is the difference between a balanced and unbalanced structural rearrangement?
Balanced rearrangements result in NO loss of genetic material; often phenotypically normal
Unbalanced rearrangements mean the chromosome set has additional or missing material; often phenotypically abnormal
What are three examples of balanced structural rearrangements?
- Inversion –double stranded segment flips around 5’-3’ to 3’-5’
- Reciprocal Translocation –exchange of broken segments
- Robertsonian Translocations –fusion of two acrocentric chromosomes within centromeric regions => loss of short arms
What is the difference between paracentric and pericentric inversions?
Paracentric inversions exclude the centromere where pericentric inversions do include the centromere
para => chromosome breakage or loss
peri => duplications and deletions
Robertsonian translocations occur most frequently on which chromosome?
Chromosome 14
~85%
What are four examples of unbalanced structural rearrangements?
- Deletion –loss of genetic material
- Duplication –gain of genetic material; generally less harmful than deletion; can result from unequal crossing-over or abnormal segregation during meiosis
- Ring chromosome –fragment circularizes and acquires kinetochore activity
- Isochromosome –one arm missing and other duplicated as mirror-image; generally observed on long arm of X chromosome; stably transmissible to offspring
What is the difference between a terminal and interstitial deletion?
Terminal = deletion on one chromosome arm
Interstitial = deleted segment with the centromere; can go from one arm to the other
On which chromosome is there a deletion for Cri-du-chat syndrome?
Chromosome 5
On which chromosome is there a deletion for Angelman syndrome?
Chromosome 15 (maternal)
On which chromosome is there a deletion for Prader-Willi syndrome?
Chromosome 15 (paternal)
On which chromosome is there a deletion for DiGeorge syndrome?
Chromosome 22
