Lecture 5 Flashcards
What is a Point Mutation?
Alteration of single base pair of DNA
What are types of Point Mutations?
Substitutions
Insertions or Deletions
What is a Substitution?
A single base pair is replaced by another. Usually, a single nucleotide is affected and during replication the complementary base pair is added
What is an Insertion of Deletion?
Adding or deleting a single base pair
What is a Transition?
A substitution that changes a purine for purine or pyrimidine for a pyrimidine
What is a Transversion?
Changing a purine for a pyrimidine or a pyrimidine for a purine
What is the source of point mutations?
- Spontaneous Replication erros
* Spontaneous Chemical Changes
What are Spontaneous Replication Errors?
- non-watson-crick base pairing causes wrong nucleotide to be incorporated
- small deletions and insertions due to strand slippage
What are Spontaneous Chemical Changes?
- Depurination (loss of purine resulting in loss of base)
* Deamination (loss of an amino group) which converts a base pair to a different base pair
How are mutations repaired?
-Base excision repair (uracil removal)
-Nucleotide excision repair(removes pyrimidine and dimers)
-Mismatch repair (incorrectly replicated DNA, after proof reading
NHEJ and HR
What are the types of Substitution mutations?
Synonymous mutation
Missense mutation (conservative)
Missense mutations (non conservative)
Nonsense mutation
What is a Synonymous mutation?
A substitution that affect a codon in a position that does not alter the encoded amino acid
What is a Missense Mutation (conservative)?
A substitution that affects a codon so that a different amino acid is incorporated but the new amino acid has similar properties as the old one
What is a Missense Mutation (non-conservative)?
A substitution that affects a codon so that a different amino acid is incorporated but the new one has different properties of the old one
What is a Nonsense mutation?
A substitution that changes a codon into a stop codon causing the the premature termination of the protein
What are the types of insertions or deletions?
Frameshift mutation
What is a Frameshift mutation?
A single base pair insertion or deletion within the reading frame will alter all codons from this point until a stop codon is encountered
What is a Silent Mutation?
A general term for mutations that have no effect on the function and sequence of encoded protein regardless of which gene is hit
What is the Degenerate Code?
64 codons encode 20 amino acids and three termination signals
What happens if there is a mutation on regulatory DNA?
Because regulatory DNA controls the activity of the gene it will affect the amount of gene product
What are Regulatory RNA elements?
Regions of the gene that are non-coding but transcribed and may be important for the regulating translation or stability of the mRNA
What happens if there is a mutation at a splice site?
Slice sites are important for RNA processing. It will affect either amount of protein or protein function
What happens if there is a mutation at a Ribosomal binding site?
It will affect the amount of protein
What is a Morph?
Contrasting but recurring forms or types within a single population of a species
What are SNPs?
Single nucleotide variations in the genome which originated from point mutation and became “fixed” in the population
What does Genetic Mosaic mean?
Contains somatic regions that are genotypically different from each other
What is a prime example of Somatic mutations?
Cancer
What do gene mutation affect?
A single gene
What doe Chromosome mutations refer to?
Changes in a region of DNA that harbours multiple genes
What is Aneuploidy?
Changes in chromosome number
What are the X and Y chromosomes?
Sex Chromosomes
What happens in abnormal meiosis?
Abnorma gametes
Errors in segregation
Nondisjunction of chromosomes
What is nondisjunction?
Failure of homologous chromosomes or sister chromatids to separate and move to opposite poles during cell division resulting in the loss or gain of a chromosome
What is Nullisomy?
Loss of both members of a homologous pair of chromosomes (2n-2)
What is Tetrasomy?
The gain of a pair of homologous chromosomes (2n+4)
What does the SHOX gene do?
Regulates growth
What is Polyploidy?
The number of chromosome sets that an organism have
What is triploid? Tetraploid?
3n and 4n
What is Autopolyploidy through mitosis?
When there is a division of sister chromatids but no cell division resulting in polyploidy
What does Colchicine do?
Inhibits microtubule polymerization and promotes non-disjunction events
what is Autopolyploidy through meiosis?
When after meiosis I the cells do not separate leaving 2 copies of the chromosomes.
How can Triploid occurs?
A 2n gamete fuses with a 1n (normal) gamete resulting in 3 copies
What is Autopolyploidy?
Extra sets of chromosomes derived from the same species, caused by accidents in mitosis or meiosis
What is Allopolyploidy?
When organisms contain 2 or more sets of chromosomes that are different species
What causes seedless plants?
odd-ploidy resulting in sterility
How can propagate sterile plants?
Cuttings grown asexually
Tetraploid plant can be crossed to diploid plans to create triploid seeds
What is Endopolyploidy?
Certain cells that are polyploid in diploid organisms. Usually found in large specialized cells
What causes Endopolyploidy?
Extra rounds of DNA synthesis with out mitosis or cytokinesis
What are the types of Chromosomal Aberrations?
Deletion
Duplication
Inversion
Translocation
What is Deletion in Chromoeomes?
Removal of a Chromosomal segment
What is Duplication in Chromosomes?
A repetition of a chromosomal segment
What is Inversion in Chromosomes?
Reversing a segment with an chromosome
What is Translocation within a chromosome?
Moving a segment from one chromosome to another
how can chromosomal deletion happen?
Two double strand breaks occur on the same chromosome and the NHEJ protein puts the incorrect fragments together
What causes terminal deletion?
When a chromosome breaks in one or more places and the piece with out a centromere is lost and degraded
What causes interstitial deletion?
When the centre portion of a chromosome is deleted and the ends rejoin
What is the consequence of chromosomal deletion?
Depends on the size of lost pieces
How may deletions and duplication occur in meiosis?
If crossing over occurs incorrectly between homologous chromosomes. Misalignment may occur by pairing at repetitive sequences resulting in a duplication and deletion on each chromosome
What is a Tandem Duplication?
Duplications on chromosomes directly after each other
What are insertional duplication?
Duplication that occurs at different parts of the chromosome twice
What is a Reverse Duplication?
When a duplicated fragment is inverted and put in the same chromosome
What is Intrachromosomal duplication and Interchromosomal duplication?
Intrachromosomal - Same chromosome
Interchromosomal - different chromsomes
What is reciprocal translocations?
A balanced exchange where one region from one chromosome is swapped with a region from another chromosome
What is the issue with reciprocal translocation?
Its not for sure which chromosomes are homologous
What are Pericentric inversion?
When the Centromere is within the inverted region
What is Paracentric inversion?
When the centromere is outside the inverted region
How does NHEJ work?
When there is a double strand break and so it cuts off the hanging ends and rejoins them because there is no template for the correct nucleotides so there is small deletion of nucleotides
What is homologous recombination?
When there is a double stand break but there is a sister chromatid to make up for the loss that occurred during the break
What are Ku proteins in NHEJ?
Proteins that sense the double stranded breaks and bind to them to recruit the appropriate machinery
What happens after Ku proteins attract machinery?
Some DNA is trimmed off and ligase re-attaches them
How does Homologous recombination work?
It uses the a sister chromosome as a template when one of the sister chromosomes is broken
