Chromosomes and Abnormalities

Question 1

How many pairs of chromosomes?

Answer 1

46 chromosomes
22 autosomal pairs
1 pair of sex chromosomes XX or XY

Question 2

What cell types can be cultured to test for cytogenetics?

Answer 2

• Blood – T-lymphocytes
• Skin / Umbilical cord / Placenta
• Bone marrow
• Solid tumour
• Amniotic fluid / Chorionic villus - Prenatal

Question 3

How are cell samples put into the process of karyotyping?

Answer 3

1. Place sample in culture medium containing PHA
2. Incubate for 48-72 hours
3. Add colcemid - inhibits spindle formation, stops cells at metaphase to see condensed chromosomes
4. Add hypotonic solution - cells swell
5. Cells dropped and fixed onto slide to spread
6. Slides are then treated with trypsin to digest proteins and giemsa to produce g banding on chromosomes
7. Slides are scanned, analysed in software.

Question 4

How are the regions numbered on chromomes?

Answer 4

Regions increase from centromere outwards.

Question 5

What is the ISCN for a normal female and normal male?

Answer 5

46,XX
46,XY

Question 6

Two types of chromosomes abnormalities:

Answer 6

Numerical, structural

Question 6

Two types of chromosomes abnormalities:

Answer 6

Numerical, structural

Question 7

Name 3 numerical chromosome abnormalities with ISCN:

Answer 7

Trisomy - Extra chromosomes at 21, Downs syndrome
47,XX,+21
Monosomy - Loss of a chromosome, Turner syndrome
45, X
Polyploidy - 3 whole sets of chromosomes, 69 XXY

Question 8

Name the 4 structural chromosome abnormalities with ISCN:

Answer 8

Translocation - Exchange of material
Inversion - Changing of orientation, no loss or gain of material
Duplication - Gain of material
Deletion - Loss of material
ISCN ?

Question 9

What is non disjunction and where does it occur?

Answer 9

When the chromosome doesn’t separate properly in meiosis.
Occurs in meiosis 1 and meiosis 2

Question 10

How does non disjunction affect meiosis 1?

Answer 10

Results in - 2 disomic gametes + 2 nullisomic gametes

Question 11

How does non disjunction affect meiosis 2?

Answer 11

Results in - 1 disomic gametes,
1 nullisomic gametes,
2 normal gametes

Question 12

How does disomic gamete and nullisomic gamete affect conceptus?

Answer 12

Disomic - Leads to trisomy
Nullisomic - Leads to monosomy

Question 13

Edwards syndrome karyotype?

Answer 13

47,XX,+18

Question 14

Patau syndrome karyotype:

Answer 14

47,XX,+13

Question 15

What is triploid karyotype?

Answer 15

3 copies of each chromosome,
Can cause …

Question 16

What is reciprocal translocation?

Answer 16

A balanced exchange of chromosomal material

Question 17

What is Robertsonian translation?

Answer 17

Centromere is at the top of the chromosome, if joined by centromere would create a new chromosome.

Question 18

What is unbalanced rearrangement?

Answer 18

A deletion of part of chromosome eg p arm of 5 chromosome