2. Cytogenetics Flashcards
Cytogenetics
The study of chromosome number, structure and function
Chromsome territory model
If chromosomes occupied distinct territories, localised damage would affect only a small subset of chromosomes
Random organisation model
If the chromatin fibres of each chromosome were randomly distributed throughout the nucleus many chromosomes would be damaged
Structural chromosome defects grouped on the basis of..
- Number of chromosome breakages
- Number of chromosomes involved
Deletions: What is it and what is the result
- Occurs when a chromosome breaks and a piece is lost
- Results in partial monosomy for that chromosome
Types of deletions
Terminal and interstitial
Example of disease where terminal deletion has occurred
Cri-du-chat (5p-), partial deletion of short arm on chromosome 5
Example of disease where interstitial deletion has occurred
Williams syndrome, deletion of elastin genes on long arm of chromosome 7
Translocation
Chromosome break and the fragments rejoin to other chromosomes
Loss of genetic material during translocation?
No, but breakpoint can disrupt a critical gene or juxtapose pieces of two genes to create a fusion gene
Translocations cause reductions in fertility?
Yes
Types of translocations
Reciprocal, Robertsonian (centric fusion), insertional
Reciprocal translocation
Exchange of material between nonhomologous chromosomes
Robertsonian translocation
Takes place between acrocentric chromosomes,. Break takes place at or near centromere
Inversion
Occur after a breakage -> chromosome fragment is inverted and rejoined (not lost!)
