Structural Chromosomal Abnormalities

Question 1

What is the difference between a balanced and unbalanced structural rearrangement?

Answer 1

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

Question 2

What are three examples of balanced structural rearrangements?

Answer 2

1. Inversion –double stranded segment flips around 5’-3’ to 3’-5’
2. Reciprocal Translocation –exchange of broken segments
3. Robertsonian Translocations –fusion of two acrocentric chromosomes within centromeric regions => loss of short arms

Question 3

What is the difference between paracentric and pericentric inversions?

Answer 3

Paracentric inversions exclude the centromere where pericentric inversions do include the centromere

para => chromosome breakage or loss
peri => duplications and deletions

Question 4

Robertsonian translocations occur most frequently on which chromosome?

Answer 4

Chromosome 14

~85%

Question 5

What are four examples of unbalanced structural rearrangements?

Answer 5

1. Deletion –loss of genetic material
2. Duplication –gain of genetic material; generally less harmful than deletion; can result from unequal crossing-over or abnormal segregation during meiosis
3. Ring chromosome –fragment circularizes and acquires kinetochore activity
4. Isochromosome –one arm missing and other duplicated as mirror-image; generally observed on long arm of X chromosome; stably transmissible to offspring

Question 6

What is the difference between a terminal and interstitial deletion?

Answer 6

Terminal = deletion on one chromosome arm

Interstitial = deleted segment with the centromere; can go from one arm to the other

Question 7

On which chromosome is there a deletion for Cri-du-chat syndrome?

Answer 7

Chromosome 5

Question 8

On which chromosome is there a deletion for Angelman syndrome?

Answer 8

Chromosome 15 (maternal)

Question 9

On which chromosome is there a deletion for Prader-Willi syndrome?

Answer 9

Chromosome 15 (paternal)

Question 10

On which chromosome is there a deletion for DiGeorge syndrome?

Answer 10

Chromosome 22