Day 2 Chromosomal Abnormalities 2

Question 1

1. Describe the mechanism(s) of common chromosomal structural rearrangements.

Answer 1

as a whole occurs by breakage and rejoining
deletion: breaks, rejoins (see slide–but ex is you have 1-4), break occurs so 2-3 break off, 1 and 4 rejoin new strand is 14
inversion: breakage occurs in same spot as in deletion, but to repair instead of deleting entire thing it is inverted so that the strain becomes 1324
Reciprocal Translocation: break occurs on two different strands (1-4 and 5-10, at 2-3 and between 7-8), the two strands join one another so new strnads are 1289(10) and 56734

Other method is Crossing over: will have same effect in reciprocal translocation as described above
Duplication can also occur (often in conjuction with deletion) where lost strand from the deletion goes to the other piece of DNA so you get 14 and 123234
Inversion is basically the same

Question 2

2. Define the differences between balanced and unbalanced structural rearrangements.

Answer 2

Balanced: Normal Complement of genetic material
Types—reciprocal translocation, robertsonian translocations, inversions
Unbalanced: Abnormal chromosomal/genetic content
deletions, duplications, isochromosomes, marker (ring) chromosomes, recombinant chromosomes

basically there is the same amt of genetic material in balanced and a different amt in unbalanced

Question 3

3. Assess the risks in families that are carriers of balanced translocations to have unbalanced progeny.

Answer 3

Ranges from 0-30% depending on type of translocation

factors affecting risk:
size of exchanged material (behavior during meiosis)
if genes are involved (DGAP)
tolerated monosomies and trisomies
sex of carrier: maternal more likely to have unbalanced offspring