Chromosome disorders

Question 1

Who invented karyotype analysis and when?

Answer 1

Tijo and Levan in 1956

Question 2

What causes mitosis?

Answer 2

Phytohemagglutinin

Question 3

How do you stop cells in metaphase?

Answer 3

Colchicine and only gross morphology is visible

Question 4

When was chromosome banding developed?

Answer 4

1970s

Question 5

Why was the Giemsa stain developed?

Answer 5

To identify the plasmodium of malaria

Question 6

After Gustav Giemsa’s death, with was added to advance karyotype techniques? What does it do?

Answer 6

G stain with trypsin on chromosomes. Banding allows one to identify major chromosome abnormalities

Question 7

What does karyotype testing allow you to do?

Answer 7

A test to identify and evaluate the size, shape and number of chromosomes in sample cells

Question 8

In a karyotype what are the dark areas and the light areas?

Answer 8

The dark areas are heterochromatin where the DNA that is condensed and not expressed. The light bands are euchromatin, the DNA that is expressed

Question 9

What is an aneuploidy?

Answer 9

Loss or gain of 1 chromosome

Question 10

What are the percentages of non-disjuction?

Answer 10

90% = maternal, 5% = paternal, 4% robertsonian translocation, 1 mosaicism

Question 11

What is a monosomy? What is the only viable monosomy?

Answer 11

Loss of one chromosome. The only viable monosomy is X0.

Question 12

What is a trisomy? Autosome examples? Sex chromosome examples?

Answer 12

Gain of a chromosome. 21/18/13 and XXY, XXX, XYY

Question 13

What causes 50% of spontaneous miscarriages?

Answer 13

Chromosomal abnormality

Question 14

What is mosaicism?

Answer 14

Presence of 2 or more cells lines with different genetic makeup in an individual

Question 15

Mosaicism - how can some cells have trisomy and others not? What about an Down syndrome embryo?

Answer 15

Non-disjuction during an early division after fertilization. A DS embryo in which some cells revert back and lose the extra chromosome

Question 16

What causes Down syndrome and what are 5 affects?

Answer 16

Trisomy 21. Low IQ, congenital heart and GI tract defects, epicanthic folds, broad nasal bridge, short stature

Question 17

What causes Edwards syndrome and what are 5 affects?

Answer 17

Trisomy 18. 90% die within first year of life, Low IQ, cardiac defects, microcephaly, micrognathia , cleft lip/palate

Question 18

What causes Patau syndrome and what are 5 effects?

Answer 18

Trisomy 13. 90% die within first year of life, Low IQ, cardiac defects, holoprosencephaly, anophtalmia, cleft lip/palate

Question 19

What is DiGeorge Sequence? What does it cause?

Answer 19

3 Mb Deletion of 22q11.2 containing 35 genes. Dysfunctional migration of neural crest cells to developing structures in the neck

Question 20

What is the important gene deleted with DiGeorge sequence?

Answer 20

TBX1

Question 21

What is a major effect of DiGeorge sequence aka Velocadiofacial syndrome?

Answer 21

Thymus and parathryroid hypoplasia