Final - Cytogenetics

Question 1

Clinical role of cytogenetics

Answer 1

• cytogenetics identifies chromosomal anomalies that may be associated with disease which contributed to the diagnosis and treatment of patients
• two categories of abnormalities = numerical and structural

Question 2

Clinical specimens used in cytogenetics

Answer 2

• blood
• bone marrow
• tissue
• amniotic fluid
• chorionic villi

Question 3

Specimen Preparations for Karyotyping

Answer 3

1. Obtain sterile sample, transport biopsies on ice
2. Alliquot into medium
3. CO2 incubation
4. Use of mitogen to encourage cell division and mitotic inhibitor to collect cells at metaphase
5. Harvest via hypotonic solution to lyse cells
6. Fix cells on slide

Question 4

Histone

Answer 4

• an alkaline protein that package and order DNA into structural units = nucleosomes

Question 5

Non-histone protein

Answer 5

• protein that remains after histones have been removed

ex: scaffold protein

Question 6

Centromere

Answer 6

• a region of a chromosome to which spindle fibers attach during cell division.
• the location of a centromes gives a chromosome its characteristic shape.
• p = short arm, q= long arm

Question 7

telomere

Answer 7

• short repeated DNA sequences located at each end of chromosomes

Question 8

nucleosome

Answer 8

• a bead-like structure composed of histone proteins wrapped with DNA

Question 9

metacentric

Answer 9

• centromere positioned in the middle of chromosome (centrally placed)

Question 10

submetacentric

Answer 10

• describes a chromosome whose centromere is placed closer to one end than the other

Question 11

acrocentric

Answer 11

• centromere placed very close to, but not at, one end

Question 12

telocentric

Answer 12

• centromere located at the terminal end of the chromosome

Question 13

3 criteria to classify and identify chromosomes

Answer 13

1. Size
2. Position of centromere
3. Banding pattern

Question 14

G-banding

Answer 14

• darkly stained G bands
• metaphase spreads are treated with trypsin and stained with Giemsa stain
• observed with light microscope

Question 15

Q- banding

Answer 15

• bright flourescent bands under UV light same as darkly stained G bands
• uses chemical quinacrine mustard

Question 16

C-banding

Answer 16

• darkly stained C band centromeric region of the chromosome corresponds to region of constitutive heterochromatin
• extract DNA from arms only so that when it is stained with Giemsa stain and observed under microscope, the centromere is stained.

Question 17

Nomenclature

• Normal Female
• Normal Male
• Mosaic
• trisomy 13
• monosomy 8
• sex chromosome anomalies
• deletions
• additions
• translocations
• inversions

Answer 17

• # of chromosome, sex chromosomes

Normal Female: 46, XX
Normal Male: 46, XY
Mosaic: 45, X / 46, XX

Numerical anomalies-
trisomy 13: 47, XX, +13
monosomy 8: 45, XY, -8
sex chromosome anomalies: 45, X or 47, XXY

Structural anomalies-

deletions: 46, XX, del (4) (p 13.2)
additions: 46, XY, dup (11) (q11.2 q11.3)
translocations: 46, XY, t (4;9) (q21.2; p22)
inversions: 46, XY, inv (9) (p11 q21.1)

Question 18

Nondisjunction

Answer 18

• the failure of homologous chromosomes to seperate properly during meiosis / mitosis

Question 19

Aneuploidy

Answer 19

• gain/loss of chromosome equaling less than one complete complement
• ex: trisomy, monosomy

Question 20

Trisomy

Answer 20

• 2n +1

- 3 copies of the same chromosome

Question 21

Monosomy

Answer 21

• 2n -1

- 1 copy of a chromosome

Question 22

Euploidy

Answer 22

• multiples of one complete chromosome complement
• haploid (n), diploid (2n), triploid (3n), tetraploid (4n)
• normal condition

Question 23

Polyploidy

Answer 23

• a chromosomal number that is a multiple of the normal haploid chromosomal set

Question 24

Down syndrome
Patau syndrome
Edwards syndrome

Answer 24

• trisomy 21
• trisomy 13
• trisomy 18

Question 25

Structural anomalies

Answer 25

- deletion - duplication - translocation - inversion

Question 26

Deletion

Answer 26

- loss of a part of a chromosome leads to partial monosomy | - terminal or interstitial

Question 27

Duplication

Answer 27

- additional copy of a chromosome segment - results in partial trisomy - terminal or interstitial

Question 28

Translocation

Answer 28

- equal exchange involving segment with respect to the normal gene arrangment

Question 29

Inversion

Answer 29

- reversal of a chromosomal segment with respect to the normal gene arrangment - pericentric or paracentric