Chromosomes, Cell Division, Meiosis and Chromosome Abnormalities Flashcards
basic structure of linear chromosomes
regions of chromosome: telomeres centromere heterochromatin euchromatin
the end-replication problem and how it is solved
primers need to be used when replicating DNA on the lagging strand. Most of these primers are replaced by DNA when they detach, however the very end primer is not able to be replaced, this means a short sequence of DNA is lost with each replication of DNA. To combat this telomeres exist at the end of chromosomes, they are repeating sequences that contain no genes. So instead of genetic material from genes being lost, non-functional DNA from telomeres is lost instead.
euchromatin
- open structure, less dense
- active genes
heterochromatin
- condensed structure
- silenced genes
centromere
constricted region joining sister chromatids, formed of repetitive satallite DNA.
kinetochore
protein complex that forms on centromere and allows the attachment of spindles
extragenic sequences of DNA
- tendemly repeated sequences: satellite and minisatellite DNA.
- SINEs (short interspersed nuclear elements
- LINEs (long interspersed nuclear elements
chromatin
DNA-protein complex
packaging of DNA
- DNA is wrapped around histone protein, forming nucleosomes.
- These nucleosomes are wrapped up themselves, 6 per turn.
- This structure is then wrapped again.
- then again to form a chromosome
purpose of packaging of DNA
- Negatively charged DNA neutralised by positive charged histone proteins
- DNA takes up less space
- Inactive DNA can be folded into inaccessible locations until required
primary laboratory technique for chromosome number abnormalities
Fluorescent in situ hybridisation (FISH)
types of FISH
- unique sequencing probes
- centromeric probes
- telomeric probes
- whole chromosome probes
centromeric probe function
Useful for determining chromosome number
Telomeric probe function
- Useful for detecting subtelomeric rearrangements
- Often present in children with unexplained mental retardation
Whole chromosome probes function
Useful for detecting translocations and rearrangements
