Mutations and genetic variation Flashcards
What is depurination?
The process by which purine bases are lost due to spontaneous hydrolyization
What is deamination?
Loss of an amine group by one of the bases–particularly cytosine (making uracil)
What is pyrimidine dimerization (in the scope of our lecture)?
When UV light dimerizes adjacent Thymine bases
What are somatic mutations?
Mutations in the genes of somatic cells–do not affect progeny
What is the result of somatic mutation early on in the development of the organism?
Mosaicism
What is a germline mutation?
A mutation in the sex cells–causes mutation in the offspring.
Variations in nucleotide sequences is what type of mutation?
Gene mutations
Rearragements, deletions, or duplications of chromosomal regions are what type of mutation?
Chromosomal
A surplus or loss of chromosomes is what type of mutation?
A genomic mutation
Changes in the methylation of DNA or in the modification of histone proteins that contribute to the control of gene expresses are what type of mutation?
Mutations impacting chromatin
What is likely to have a greater impact: mutations at the chromosomal level, or at the genome level?
Chromosomal –multiple genes may be affected
What are the four types of point mutations?
- Silent
- missense
- Nonsense
- insertion/deletion
A change in a single base that does not result in the change of the protein that the codon encodes is what type of point mutation?
Silent
A change in a single base that results in a single codon/amino acid to change is what type of point mutation?
Missense
A change in a single base that results in premature stopping of translation of the polypepetide is what type of point mutation?
Nonsense
What are three factors that contribute to small insertions/deletions
- Incorrect recombination
- Strand slippage
- Intercalating agents
Unequal crossover due to the presence of very similar base pairing between two separate chromosomes is what type of insertion/deletion?
Incorrect recombination
A DNA segment that has a repetitive sequence may inadvertently loop out during replication and cause a deletion during replication. What is the name for this type of insertion/deletion
Strand slippage
Insertion or deletion of a number of bases, n, where n=3x and x=1,2,3… results in what type of mutation?
Frameshift mutation
What is the process by which homologous chromosomes line up?
Synapsis
The protein complex that holds the homologous chromasomes together is called what?
Synaptonemal complex
What are chisasmata?
The sites of chromosomal crossover
Are genes that are close to each other on a chromosome more or less likely to crossover?
Less likely–the closer they are together, the more likely they are to be inherited together.
What is the condition where there is an extra copy of a chromosome?
Trismony
What is the condition where there is one less chromosome than usual?
Monosomy
True or false: monosomy of an autosome can produce viable offspring
False
Which autsomes can have an extra pair and still produce viable offspring?
13, 18, 21
What is the condition called when there is an extra copy of chromosome 13?
Patau syndrome
What is the condition called when there is an extra copy of chromosome 18?
Edward syndrome
What is the condition called when there is an extra copy of chromosome 21?
Down syndrome
What is the term for having the same genotyped cells within the same individual
Mosaicisim
How does the exonuclease activity of DNA polymerase delta contribute to the accuracy of DNA replication?
By proofreading the bases it inserts as it transcribes DNA.
If there is an issues in one of the DNA strands being replicated, how do enzymes tell which one is the new one and which is the original?
There are nicks in the new one. Helix distortions are also specifically recognized
What is Lynch syndrome (HNPCC)?
A disease caharacterized by the propensity of DNA to mutate due to defects in the DNA repair mismatch system.
Increased colorectal cancer
What is the function of DNA glycosylases?
Recognize specific altered/damaged bases and repair them.
When is nucleotide excision repair utilized?
Where there are large changes in the structure of DNA (e.g. pyrimidine dimers)
What is xeroderma pigmentosum?
A disease characterized by an extreme sensitivity to sunlight, skin pigment changes, and skin cancers due to a defect in the nucleotide excision repair mechanism.
What is non-homologus end joining?
When breaks in DNA occur in two different strands, the chains are simply ligated back together, resulting in the loss of a nucleotide(s).
Why does non-homologus end joining work without critical damage to the cell?
Most of the DNA does not encode protein; ligated areas are not expressed
What is the process by which a homologus chromosome is used as a template to repair another chromosome?
Homologous end-joining.
What is cytrabine? How does it work?
Inhibitor of DNA repair process.
Has an arabinose instead of ribose, causing it to be converted to cytrabine trisphosphate. Cytrabine trisphosphate then competes with DNAs, and thus blocks replication
What is cyclophosphamide? How does it work?
Treatment for hodgkins.
It is converted to phosphoramide mustard, which is a bi-functional alkylating agent, forming intrastrand DNA cross links.
What is doxorubicin? How does it work?
Anti-cancer agent that inhibits topoisomerase II, leading to doube strand breaks
Where do strand slippages usually occur?
Where there are repetitive areas of bases.
What is the order for repairing a spontaneous conversion of Cytosine to uracil (4 steps)?
- Uracil DNA glycosylase excises theuracil
- AP endonuclease breaks the local phosphodieaser bond
- DNA phophodiesterase removes the phosphate backbone of the a-purinc base
- DNA pol tries again
What is the order of nucleotide exicision repair?
- Nucleases/helicases remove the bad segment
2. DNa Pol and ligase repair
A defect in the nucleotide excision repair mechanism can lead to what disease?
Xeroderma pigmentosum
