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).
