Lecture 47

Question 1

There are 4 major types of chromosome rearrangements, each with 2 subtypes. What are they?

Answer 1

Deletions - terminal and interstitial deletion

Duplication - tandem and insertional

Inversion - pericentric and paracentric

Translocation - reciprocal and robertsonian

Question 2

Which chromosome rearrangements are unbalanced?

Answer 2

deletions and duplications

Question 3

Which chromosome rearrangements are balanced?

Answer 3

inversions and translocation

Question 4

Deletions are unbalanced. Why?

What are the two types of deletions?

Answer 4

loss of genetic material; harmful

terminal deletion: missing the end of a chromosome

interstitial deletion: missing an internal segment

Question 5

Cri du chat syndrome is del(5)(p15.1). What type of chromosome rearrangement is it?

Answer 5

terminal deletion

Question 6

Duplications are unbalanced. Why?

What are the two types of duplications?

Answer 6

gain of genetic material, usually less harmful than deletions

tandem duplication - duplicated segment placed next to original

insertional duplication - duplicated segment inserted elsewhere

Question 7

Inversions are balanced. Why?

What are the two types of inversions?

Answer 7

no gain/loss of genes - just flipped orientation

pericentric inversion - includes the centromere

paracentric inversion - does not include the centromere

usually benign

Question 8

Translocations are balanced. Why?

What are the two types of translocations?

Answer 8

segments of chromosomes swap location

reciprocal translocation - mutual exchange

Robertsonian translocation - fusion of acrocentric chromosomes

Question 9

What are the two causes for chromosome rearrangements?

Answer 9

improper NHEJ and NAHR

Question 10

Why might chromosome rearrangements be a result of improper NHEJ?

Answer 10

radiation causes dsDNA break, NHEJ repair incorrectly, joining the wrong ends

leads to any chromosome rearrangement depending on break orientation

two breaks, middle piece lost = interstitial deletion

Question 11

Why might chromosome rearrangements be a result of NAHR (non allelic homologous recombination)?

Answer 11

happens during prophase I of meiosis (crossing over)

TE provide repeated sequences

crossover between wrong repeated sequences = rearrangement

only 2/4 gametes produced will carry the rearrangement

Question 12

Which of the unbalanced rearrangements are more dangerous?

Answer 12

deletions are more harmful than duplications

homozygous deletions = lethal

heterozygous deletions = survivable if small

Question 13

Which of the balanced rearrangements causes problems?

Answer 13

Translocations: usually no phenotype in carriers, but cause problems in meiosis (abnormal gamete)