Clinical Cytogenetics

Question 1

What are cytogenetic disorders?

Answer 1

Large scale chromosome disorders (in # or structure)

Question 2

Cytogenetic disorders are responsible for __% of all live births, __% of all pregnancies older than 35, and __% of all spontaneous 1st trimester abortions.

Answer 2

1%, 2%, and 50%

Question 3

What are the 5 reasons for doing prenatal clinical cytogenetic testing?

Answer 3

1) Maternal age >35
2) Abnormal serum quad screen results (a blood test)
3) Abnormal ultrasound
4) Family Hx of chromosome abnormalities
5) Parental anxiety

Question 4

What are the 6 reasons for doing clinical cytogenetic testing later in life?

Answer 4

1) If mom has had 2 or more miscarraiges
2) Birth defect at birth
3) Mental retardation
4) Ambiguous genitalia
5) Unexplained growth or development abnormalitites
6) Asses chromosomal complement in tumor cells

Question 5

In what three ways are chromosomes identified during cytogenetic visualization?

Answer 5

By their overall size, centromere position, and banding patterns

Question 6

What are 4 examples of source tissue for performing cytogenetic testing?

Answer 6

1) Nucleated white cells from blood
2) Amniotic fluid (fetal) and placental (maternal + fetal) cells
3) Tumor cells
4) Bone marrow

Question 7

What is a picture of individual chromosomes from mitosis, arranged by chromosome number called?

Answer 7

Karyotype

Question 8

At what number do the bands for G-staining start, and where are those first bands?

Answer 8

11 starts at the centromere and then numbers increase as you move towards the ends of the short and long arms.

Question 9

What countries use G-bands and what regions are stained dark when using G-band stains?

Answer 9

The U.S.A labs use G-bands to make the gene-poor A/T regions dark

Question 10

What does Q-band stand for?

Answer 10

Quinacrine mustard banding (not commonly used)

Question 11

True or False: Both G and R staining require that the chromasomes be incubated with the stain.

Answer 11

True

Question 12

What countries us R-banding (and why) and what regions of the chromasome are stained darkly.

Answer 12

Common in European labs (because it’s easier to analyze than G-bands), where the gene-rich G/C regions are stained dark.

Question 13

What does C-banding stain?

Answer 13

Constitutive heterochromatin at the centromeres and distal parts of Yq

Question 14

What does High Resolution Banding stain?

Answer 14

Prometaphase chromosomes, which are less condensed so the bands are more resolved

Question 15

What are fragile sites?

Answer 15

Nonstaining gaps in chromosomes

Question 16

True or False: G banding of less condensed chromosomes (e.g. prophase chromosomes instead of metaphase chromosomes) produces higher resolution pictures so that more bands can be discered individually.

Answer 16

True

Question 17

What are marker chromosomes on a karyotype?

Answer 17

Chromosomes that are so abnormal that they can’t be identified.

Question 18

True or False: G banding CANNOT detect small chromosomal deletions.

Answer 18

False: G-banding is perfectly capable of detecting small deletions.

Question 19

True or False: SKY CANNOT detect small chromosomal deletions.

Answer 19

True

Question 20

What is comparative genome hybridization (CGH)?

Answer 20

Combine patient’s DNA (red) with control DNA (green) and put on the oligo plate. Yellow means patient and control have the same sequence. Red means patient’s DNA is over expressed, Green means patient’s DNA was underexpressed.

Question 21

What is CGH useful for? What is it not useful for?

Answer 21

It is very sensitive in detecting small deletions, but it does not detect translocations or inversions because the DNA is still present, just in the wrong place.