Chromosome Abnormalities

Question 1

How long does it take the cell cycle to complete?

Answer 1

24 hours

Question 2

What is used to culture t-lymphocytes?

Answer 2

Blood

Question 3

Explain the endothelial cell culture process

Answer 3

Add the sample to culture medium which contains PHA (phytohaemagglutinin)
Leave the sample proliferate at 37°c for 48-72 hours
Then add colcemid ( drug that inhibits spindle formation in metaphase causing the cell cycle to arrest to get the maximum number of cells in metaphase )
Hypotonic solution is then added which causes the cells to swell
Cells are then dropped and fixed on a slide to allow the chromosomes to spread nicely
Slides are then treated by trypsin ( an enzyme that breaks down peptones into smaller peptides )
The trypsin digests the proteins and dyes them producing the characteristic banding patterns
The slides are then scanned and analysed on a software using computer technology ( karyotyping )

Question 4

What is phytohaemagglutinin?

Answer 4

A plant derived alkaloid that stimulates t-lymphocytes to divide in the test tube

Question 5

Chromosomal abnormality numerical (trisomy)

Answer 5

47, xx, +21

Question 6

Chromosomal abnormality numerical (monosomy)

Answer 6

45,x

Question 7

Chromosomal abnormality numerical (polyploidy)

Answer 7

69,xxy

Question 8

Frequency of chromosome abnormalities (overall)

Answer 8

1 in 200

Question 9

Frequency of chromosome abnormalities (trisomy 21)

Answer 9

1 in 700

Question 10

Frequency of chromosome abnormalities (trisomy 18)

Answer 10

1 in 3000

Question 11

Frequency of chromosome abnormalities (trisomy 13)

Answer 11

1 in 5000

Question 12

What is nondisjunction?

Answer 12

A condition in which pairs of homologous chromosomes fail to separate during meiosis or a chromosome fails to divide at anaphase of mitosis or meiosis resulting in a cell with an abnormal number of chromosomes

Question 13

How many births does down syndrome affect?

Answer 13

1/1000 births

Question 14

Features of Down syndrome in childhood

Answer 14

Hypotonia
Developmental delay
Learning difficulties
Heart problems
Digestive problems
Distinctive facial features ( flat facial features, small head & ears, short neck, bulging tongue, epicanthic neck folds, atypically shaped ears )
Single palmar crease

Question 15

Features of down syndrome in adulthood

Answer 15

Cataracts
Leukaemia
Obesity
Life expectancy ~ 60

Question 16

What is F.I.S.H?

Answer 16

Label the probe with fluorochrome

Separate DNA to single stranded

Hybridise these probes onto the target DNA

Use a fluorescent microscope to light probe, we can count chromosomes in the nuclei and look for submicroscopic deletion using loci specific probes which we can identify abnormalities more clearly and look for specific rearrangements such as gene fusions in acquired abnormalities

Question 17

What are constitutional abnormalities?

Answer 17

Occur at gametogenesis

Usually affect all cells in the body

Can be heritable

Question 18

What a acquired abnormalities?

Answer 18

Change during a patients lifetime

Associated malignant changes generally restricted to malignant tissues

Not heritable

Question 19

What is the role of cytogenetics in acquired abnormalities?

Answer 19

Confirmation of malignancy

Classification of a disease type

Prognosis

Monitoring

Question 20

What is reciprocal translocation?

Answer 20

Occurs when part of one chromosome is exchanged with another

Question 21

What can translocation cause?

Answer 21

Can disrupt functional parts of the genome and have implications for protein production with phenotypic consequences

Question 22

What is robertsonian translocation?

Answer 22

The whole of a chromosome is joined end to end with another

Question 23

What chromosomes are involved with robertsonian translocation, and why?

Answer 23

13,14, 15, 21 and 22

Because the ends of their short arms have similar repetitive DNA sequences that predispose to their fusion

Question 24

What is Edward’s syndrome/Trisomy 18?

Answer 24

When babies have more of chromosome 18 in some or all of the cells in their body

Question 25

What is Patau’s syndrome/Trisomy 13?

Answer 25

An additional copy of chromosome 13

Question 26

What do cytogenetics do?

Answer 26

They look for constitutional abnormalities

Question 27

What do micro arrays do?

Answer 27

They investigate the genome at a higher resolution than possible by microscopy

Question 28

Which of the following most accurately describes an individual with the karyotype: “45,X”

Answer 28

Female with Turner syndrome