Chromosomal Anomalies - Number

Question 1

What is the telomere and what is its function?

Answer 1

• The cap to the DNA and protein.

- It ensures replication to the tip.

Question 2

How do light bands differ from dark bands?

Answer 2

1 - Light bands replicate earlier in the S phase than dark bands.

2 - Light bands contain less condensed chromatin than dark bands.

3 - Light bands are transcriptionally active whereas dark bands are not.

4 - Light bands are gene and GC rich whereas dark bands are AT rich.

Question 3

What is comparative genomic hybridisation?

Answer 3

A method for determining the number of copies of a sequence under investigation from an array of DNA probes.

Question 4

How are chromosomal anomalies classified?

Answer 4

1 - Numerical.

2 - Structural.

3 - Relating to different cell lines (mosaicism).

Question 5

List 2 types of numerical chromosomal anomalies.

Answer 5

1 - Aneuploidies.

2 - Polyploidies.

Question 6

List 4 types of structural chromosomal anomalies.

Answer 6

1 - Translocations.

2 - Deletions.

3 - Duplications.

4 - Inversions.

Question 7

What is a reciprocal translocation?

Answer 7

Exchange of segments of non-homologous chromosomes.

Question 8

Define acrocentric.

Answer 8

Having the centromere situated so that one chromosomal arm is much shorter than the other.

Question 9

What is a Robertson translocation?

Answer 9

The fusion of the whole long arms of two non-homologous acrocentric chromosomes.

Question 10

How does the karyotype of a person with Down syndrome differ from that of a regular karyotype?

Answer 10

There is an extra chromosome 21 (trisomy 21).

Question 11

List 5 symptoms of triple X syndrome.

Answer 11

1 - Weak muscle tone.

2 - Increased height.

3 - Kidney abnormalities.

4 - Epicanthal folds.

5 - Widely spaced eyes.

Question 12

What do the letters ‘p’ and ‘q’ signify?

Answer 12

• ‘p’ is the short arm of a chromosome.

- ‘q’ is the long arm of a chromosome.

Question 13

What is the cause of fragile X syndrome?

Answer 13

• A mutation in the FMR1 gene.

- FMR1 is a protein that regulates the production of other proteins and plays a role in the development of synapses.

Question 14

How does the karyotype of a person with Klinefelter syndrome differ from that of a regular karyotype?

Answer 14

Males have an extra X chromosome (XXY).

Question 15

List 5 symptoms of Klinefelter syndrome.

Answer 15

1 - Taller than average stature.

2 - Longer legs.

3 - Shorter torso.

4 - Broader hips.

5 - Absent, delayed or incomplete puberty.

Question 16

List 3 autosomal abnormalities and describe their karyotypes.

Answer 16

1 - Down syndrome: 47, XX + 21.

2 - Edwards syndrome: 47, XX + 18.

3 - Patau syndrome: 47, XX + 13.

Question 17

List 4 sex chromosome abnormalities and describe their karyotypes.

Answer 17

1 - Turner syndrome: 45, X.

2 - Klinefelter syndrome: 47, XXY.

3 - Jacob syndrome: 47, XYY.

4 - Triple X syndrome: 47, XXX

Question 18

Why is it important to look for miscarriages when analysing a family tree?

Answer 18

Because chromosomal findings are common in early spontaneous abortions.

Question 19

Why do the first individuals in the family line with a Robertsonian translocation not experience symptoms?

What is the danger of being a carrier of a Robertsonian translocation?

Answer 19

• Because they still have the normal number of chromosomes. They are just arranged differently.
• The danger is when both the robertsonian translocation (e.g. t(14q21q)) and one of the other non-translocated genes (e.g. 14 or 21) are inherited together (creates an aneuploidy as gametes only need one copy of any chromosome).

Question 20

List 2 hypotheses that explain why having multiple copies of normal genes causes aneuploidy phenotypes.

Answer 20

1 - Gene dosage effect.

2 - Amplified developmental instability.

Question 21

What is the gene dosage effect?

Answer 21

A hypothesis that the features of a syndrome are caused by having 1.5x the normal amount of specific gene products.

Question 22

What is amplified developmental instability?

Answer 22

A hypothesis that the features of a syndrome are caused by the overall effect of imbalance on development.

Question 23

List 3 ways in which gene expression can be affected.

Answer 23

1 - Regulation of transcription of individual genes.

2 - Differential splicing of transcripts.

3 - Multiple genes acting together in developmental pathways.

Question 24

How do we determine which genes are acting when?

Answer 24

By using in-situ hybridisation (using specially designed antisense RNA).

Question 25

What is non-disjunction?

Answer 25

Where chromosomes do not split evenly during meiosis, resulting in disomic gametes and nullisomic gametes.

Question 26

Is the meiotic error of Down syndrome more likely to be due to maternal or paternal error?

Answer 26

Maternal.

Question 27

Is the meiotic error of Edwards syndrome more likely to be due to maternal or paternal error?

Answer 27

Maternal.

Question 28

Is the meiotic error of Patau syndrome more likely to be due to maternal or paternal error?

Answer 28

Maternal.

Question 29

Is the meiotic error of Turner syndrome more likely to be due to maternal or paternal error?

Answer 29

Paternal.

Question 30

Is the meiotic error of Triple X syndrome more likely to be due to maternal or paternal error?

Answer 30

Maternal.

Question 31

Is the meiotic error of Klinefelter syndrome more likely to be due to maternal or paternal error?

Answer 31

Neither (equal).

Question 32

Is the meiotic error of Jacob syndrome more likely to be due to maternal or paternal error?

Answer 32

Paternal (never maternal).

Question 33

Why do genetic abnormalities appear to be associated with an increase in maternal age?

Answer 33

• There is a possible lengthy interval between the onset and completion of meiosis in females.
• Accumulating effects on the oocytes during this phase may damage the cell’s spindle formation and repair mechanisms.

Question 34

List 2 symptoms of Edward syndrome.

Answer 34

1 - Heart malformations.

2 - Kidney malformations.

Question 35

List 3 symptoms of Patau syndrome.

Answer 35

Affects midline formations:

1 - Incomplete lobatino of the brain.

2 - Cleft lip.

3 - Congenital heart disease.

Question 36

List 3 symptoms of Klinefelter syndrome.

Answer 36

1 - Infertility.

2 - Poorly developed secondary sexual characteristics.

3 - Tall height.

Question 37

List 3 symptoms of Turner syndrome.

Answer 37

1 - Short stature.

2 - Primary amenorrhoea (absence of menstrual period).

3 - Coarctation (narrowing) of the aorta.