Chromosomal Anomalies - Number Flashcards
What is the telomere and what is its function?
- The cap to the DNA and protein.
- It ensures replication to the tip.
How do light bands differ from dark bands?
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.
What is comparative genomic hybridisation?
A method for determining the number of copies of a sequence under investigation from an array of DNA probes.
How are chromosomal anomalies classified?
1 - Numerical.
2 - Structural.
3 - Relating to different cell lines (mosaicism).
List 2 types of numerical chromosomal anomalies.
1 - Aneuploidies.
2 - Polyploidies.
List 4 types of structural chromosomal anomalies.
1 - Translocations.
2 - Deletions.
3 - Duplications.
4 - Inversions.
What is a reciprocal translocation?
Exchange of segments of non-homologous chromosomes.
Define acrocentric.
Having the centromere situated so that one chromosomal arm is much shorter than the other.
What is a Robertson translocation?
The fusion of the whole long arms of two non-homologous acrocentric chromosomes.
How does the karyotype of a person with Down syndrome differ from that of a regular karyotype?
There is an extra chromosome 21 (trisomy 21).
List 5 symptoms of triple X syndrome.
1 - Weak muscle tone.
2 - Increased height.
3 - Kidney abnormalities.
4 - Epicanthal folds.
5 - Widely spaced eyes.
What do the letters ‘p’ and ‘q’ signify?
- ‘p’ is the short arm of a chromosome.
- ‘q’ is the long arm of a chromosome.
What is the cause of fragile X syndrome?
- 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.
How does the karyotype of a person with Klinefelter syndrome differ from that of a regular karyotype?
Males have an extra X chromosome (XXY).
List 5 symptoms of Klinefelter syndrome.
1 - Taller than average stature.
2 - Longer legs.
3 - Shorter torso.
4 - Broader hips.
5 - Absent, delayed or incomplete puberty.
List 3 autosomal abnormalities and describe their karyotypes.
1 - Down syndrome: 47, XX + 21.
2 - Edwards syndrome: 47, XX + 18.
3 - Patau syndrome: 47, XX + 13.
List 4 sex chromosome abnormalities and describe their karyotypes.
1 - Turner syndrome: 45, X.
2 - Klinefelter syndrome: 47, XXY.
3 - Jacob syndrome: 47, XYY.
4 - Triple X syndrome: 47, XXX
Why is it important to look for miscarriages when analysing a family tree?
Because chromosomal findings are common in early spontaneous abortions.
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?
- 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).
List 2 hypotheses that explain why having multiple copies of normal genes causes aneuploidy phenotypes.
1 - Gene dosage effect.
2 - Amplified developmental instability.
What is the gene dosage effect?
A hypothesis that the features of a syndrome are caused by having 1.5x the normal amount of specific gene products.
What is amplified developmental instability?
A hypothesis that the features of a syndrome are caused by the overall effect of imbalance on development.
List 3 ways in which gene expression can be affected.
1 - Regulation of transcription of individual genes.
2 - Differential splicing of transcripts.
3 - Multiple genes acting together in developmental pathways.
How do we determine which genes are acting when?
By using in-situ hybridisation (using specially designed antisense RNA).
What is non-disjunction?
Where chromosomes do not split evenly during meiosis, resulting in disomic gametes and nullisomic gametes.
Is the meiotic error of Down syndrome more likely to be due to maternal or paternal error?
Maternal.
Is the meiotic error of Edwards syndrome more likely to be due to maternal or paternal error?
Maternal.
Is the meiotic error of Patau syndrome more likely to be due to maternal or paternal error?
Maternal.
Is the meiotic error of Turner syndrome more likely to be due to maternal or paternal error?
Paternal.
Is the meiotic error of Triple X syndrome more likely to be due to maternal or paternal error?
Maternal.
Is the meiotic error of Klinefelter syndrome more likely to be due to maternal or paternal error?
Neither (equal).
Is the meiotic error of Jacob syndrome more likely to be due to maternal or paternal error?
Paternal (never maternal).
Why do genetic abnormalities appear to be associated with an increase in maternal age?
- 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.
List 2 symptoms of Edward syndrome.
1 - Heart malformations.
2 - Kidney malformations.
List 3 symptoms of Patau syndrome.
Affects midline formations:
1 - Incomplete lobatino of the brain.
2 - Cleft lip.
3 - Congenital heart disease.
List 3 symptoms of Klinefelter syndrome.
1 - Infertility.
2 - Poorly developed secondary sexual characteristics.
3 - Tall height.
List 3 symptoms of Turner syndrome.
1 - Short stature.
2 - Primary amenorrhoea (absence of menstrual period).
3 - Coarctation (narrowing) of the aorta.
