Cytogenetics And Learning Disorders Part 4

Question 1

What are the disadvantages of G-band chromosome analysis?

Answer 1

• resolution is relatively low (3-5Mb)

- requires viable tissue

Question 2

What is C-banding?

Answer 2

This is where constitutive heterochromatin (non-coding genetic material; present in peri-centromeric regions) stains dark and euchromatin regions remain pale.

It is useful for excluding variants or establishing the significance of markers

Question 3

What is silver staining?

Answer 3

Uses silver nitrate and results in a dark deposit corresponding to the satellite stalks of the acrocentric chromosomes.

Not all acrocentric chromosomes will be positive for silver nitrate due to heritable variation . It can used to determine if a marker chromosome is derived from an acrocentric chromosome as that part of the marker would be non-coding

Question 4

What’s are the pros and cons of FISH?

Answer 4

Pros = high resolution, can provide positional info when combined with chromosome preparations, can be used on uncultured material
Cons = targeted (specific question for specific answer)

Question 5

What are the advantages of G-band chromosome analysis?

Answer 5

• allows a genome wide screen
• untargeted analysis
• provides positional information

Question 6

What are the pros of arrayCGH?

Answer 6

• high resolution
• genome wide
• untargeted
• does not require viable tissue or cell culture

Question 7

What are the cons of arrayCGH?

Answer 7

• detects genetic imbalance only, not imprinting although can detect UPD if a SNP array is used
• provides no positional info
• mosaics may not be detected

Question 8

What is the current procedure for genetic investigation in LD?

Answer 8

Investigate proband by arrayCGH. However, this doesn’t provide positional info and may fail to detect mosaicism therefore follow up may be required:

• metaphase FISH
• Gbanding