Chromosomal Instability Flashcards
What is chromosomal instability?
A distribution of chromosomes deviating from the modal number, or an elevated frequency of chromosome gains/losses
What is CIN?
Chromosomal instability
What do CIN cells and cancer cells have in common? (4)
- Microsatellite instabilities
- Aneuploidy
- Polyploidy
- Chromosomal rearrangements
What is a microsatellite instability?
DNA mismatch repair in inhibited in microsatellite (repeating) areas
What are the two ways a CIN can arise?
Spontaneously or in response to carcinogens
What are CINs caused by?
Defects in proteins or enzymes essential for DNA repair and chromosomal maintenance
What does diagnosis of a CIN compose of?
- Genetic testing
- Evaluation of chromosomal breakage
What are 4 well known CIN examples?
- Louis Bar - Lack of coordination/dilated blood vessels
- Bloom Syndrome - skin changes/immune deficiency/cancer
- Fanconi Anemia - genomic instability/cancer
- Nijmegen breakage syndrome - microcephaly, growth retardation
What is a microsatellite?
A short repetitive DNA sequence (1-9 base pairs)
What are the 3 major uses of microsatellites?
- Genetic Mapping
- Population genetics - study diversity/relationships
- Forensic analysis - DNA fingerprinting
How many human microsatellites are sequenced?
1.4 million
What are the minimum length requirements in repeats for a mononucleotide? Dinucleotide? Other?
12 repeats - 6 repeats - 4 for others
How do microsatellites evolve?
Duplication errors in mitosis
What can be said about the mutation of DNA satellites?
They have a higher mutation rate through insertions/deletions
When are microsatellites more important for genetic diversity and evolution?
In viral genomes
What are the roles of microsatellites?
Modulation of:
1. Transcription Factor Binding
2. Spacing between promotor regions
3. Cytosine methylation
4. Alternative splicing
5. mRNA stability
6. Selection of transcription sites in alternative splicing
7. Nucleosome/chromatin structure
8. Noncoding RNA
9. Meiotic recombination hotspots
How much of the human genome is variable and used for forensics? What are these sequences called?
0.5% - polymorphic sequences
What is the STR?
A short tandem repeats do not control known traits and have no known functions
What is the TH01 STR? How does it present/vary in people?
TCAT has a different number of repeats in different alleles
What are the numerical number of chromosomes in an aneuploid vs euploid individual?
Aneuploid:
2n-1
2n
2n + 1
etc
Euploidy
2n
3n
4n
etc
What is the role of colchicine?
It is an antimitotic plant metabolite and inhibits the microtubule formation -> mitotic spindle
How does colchicine contribute to plant polyploidy?
It arrests cells in anaphase
What is a clinical use of colchicine?
It prevents the proliferation of tumor cells
What is trisomy?
2n+1 chromosomes
What is the most well known trisomy?
trisomy 21 - down syndrome
What is the process to analyze a fetus?
Karyotyping protocol is the sampling of chorionic villus in the placenta
What stage of cell division are cells in when they are harvested for karyotyping?
Metaphase
What are the common targets of trisomy screening?
Chromosomes 21, 18, 13
Karyotyping finds abnormalities in what percent of pregnancies?
2-3%
What are the two types of staining for the karyotype screening?
Classic FISH
SKY - labelling - different colors for different targets
What is the FISH protocol?
Fluorescence In Situ Hybridization:
- Designing of complementary fluorescent probes
-Denaturing the sample
-Hybridizing probes to samples
-fluorescence microscope
What are the 5 variations in chromosome structure?
- Deletion
- Duplication
- Inversion
- Non reciprocal translocation
- Reciprocal translocation
What could duplications lead to?
Gene redundancy and CNV (copy number variations)
What is an UFB?
An ultrafine bridge is an under replicated DNA that is not resolved before mitosis
What is a one ended DSB? What can it give rise to?
A one ended double strand break can give rise to an acentric fragment which can lead to a micronuclei
When could a fully duplicated chromosome lead to a micronuclei formation?
When there is lagging chromosomes from kinetochore or microtubule problems
What are the three mechanisms of polyploidy/polyteny?
- Cytokinesis failure
- Mitotic slippage
- endocycling
What stages of cell division fail in mitotic slippage and endocycling?
Slippage - metaphase
Endocycling - Ends after G2 phase
What are CIN cells called in their first stage after being normal tissue
tumorigenic
What are some characteristics that tumorigenic cells can acquire as their CIN increases?
Drug Resistance and Metastasis
What happens to metastatic cells after they undergo more severe CIN?
Cell death
What are most solid human tumors attributed to?
Chromosomal instability
What are the three impacts of genomic/chomosomal instability?
Cancer, telomere dysfunction, aneuploidy hypothesis
What are the controversial aspects of chromosomal instability and carcinogenesis?
- Genomic instability early or late event?
- Genomic = driving force?
- Genomic = necessary for tumors?
How many antibodies are in adult blood?
3-9 million
How do lymphocytes vary so much?
Genesplicing system called translocation that takes genes and puts them in different genes along the chromsome
Will antibody alleles of the mother or father be expressed?
Both, each b lymphocyte expresses one parent at a time
What are the VDJ genes?
V = variable
D = diversity
J = joining
What are the forms of antibody diversity?
- Combinatorial diversity - Each B cell randomly selects a V, D, or J cell
- Junctional diversity - addition or deletion of nucleotides at junctions of VDJ
- Somatic Hypermutation: After antigen exposure, immune cells undergo point mutation at a high rate -> affinity maturation
How many VDJ segments does a heavy chain have to choose from?
V = 38-46
D = 23
J = 6
