Microdeletions and Genomic Imbalance

Question 1

What is Wolf-Hirschhorn Karyotype and what chromosomes does it involve?

Answer 1

caused by terminal deletion of chromosome 4p

Question 2

What is the critical region?

Answer 2

deletion of a particular chromosome segment that is related with a specific abnormal phenotype

Question 3

What is contiguous gene syndrome?

Answer 3

??

Question 4

What is segmental aneuploidy syndrome?

Answer 4

??

Question 5

What is microdeletion syndrome?

Answer 5

chromosome deletions (partial monosomies) that cause genetic abnormalities

Question 6

What is pathogenic CNV?

Answer 6

copy number variation that can cause abnormal phenotypes

Question 7

What is DNA dosage gain or loss?

Answer 7

??

Question 8

Are telomeres commonly affected by microdeletions?

Answer 8

yes. they are often the target of microdeletions.

Question 9

What is Prader-Willi syndrome?

Answer 9

interstitial deletion encompassing on the proximal 15q arm. 15q12 is deleted. Causes hypotonia in infancy, childhood hyperphagia and obesity, mental retardation.

Question 10

Describe normal crossing over.

Answer 10

exchange between homologous chromosomes with perfect alignment and equal exchange.

Question 11

What are low copy repeats (LCRs)?

Answer 11

small segments of DNA in a chromosome that are highly homologous and repeated. They have greater potential to misalign and cause genetic replication errors.

Question 12

What is FISH? What is a limitation of it?

Answer 12

fluorescence in situ hybridization is a technique to detect absence or presence of specific chromosome segments using fluorescent probes.
Limited because it only tests for absence of one small segment. If test is negative, you only know that there was nothing wrong with that segment.

Question 13

What is a chromosomal microarray?

Answer 13

looks for genetic imbalances across entire genome. Doesn’t tell you anything about what the chromosomes look like though

Question 14

What color is a monosomy on a chromosomal microarray?

Answer 14

red spot for loss (the control chromosomal set is red so it binds more than the missing, green unknown with the monosomy)

Question 15

What color is a trisomy in a chromosomal microarray?

Answer 15

green spot for gain

Question 16

What color is a normal chromosome pair on a chromosome microarray?

Answer 16

yellow for no change

Question 17

Will a microarray detect a balanced chromosome rearrangement?

Answer 17

No. It only detects imbalances

Question 18

Will arrays pick up triploidy?

Answer 18

No. Even though this is a huge imbalance, the chromosomes are the same size and do not show up as imbalanced.

Question 19

Which is usually more severe: monosomy or trisomy?

Answer 19

monosomy. Trisomy you have all the necessary genes, just too much of them. Monosomy you are missing things

Question 20

Which is generally more severe: microdeletion or microduplication?

Answer 20

microdeletions are generally more severe because you are missing material instead of having too much

Question 21

Do older mothers have a higher risk of microdeletions in offsrping?

Answer 21

no. The risk increases for nondisjunction