Types of mutations Flashcards
what are the small scale mutations?
a. point mutation
b. substitutions
c. inversion
d. insertion
e. deletion
what are the large scale mutations?
chromosomal rearrangements
a. deletion, replication, inversion, translocation
what are copy number variations?
A type of genetic variation where the number of copies of a particular gene/region of a genome differs from one individual to another
what are mobile genetic element (transposable element)-induced mutations?
Sequences of DNA that can change their position within the genome –> the ability to move/”transpose” can lead to various types of mutations and genetic variations
how can point mutations be classified by?
amino acid changes (synonymous vs nonsynonymous mutations) and DNA sequence changes (transition vs transversion mutations)
what are transition mutations?
Purine → purine ; pyrimidine → pyrimidine
what are transversion mutations?
Purine → pyrimidine ; pyrimidine → purine
which bases are purines and which bases are pyrimidines?
purines: G, A
pyrimidine: C, T
synonymous mutations
A change in a nucleotide in the DNA sequence that codes for amino acids in a protein sequence but does NOT change the encoded amino acid sequence
aka silent mutation
nonsynonymous mutations and the different subtypes?
mutations in a single nucleotide that RESULTS in an amino acid sequence change
a. missense
b. nonsense/stop-gain
c. stop-loss
d. start-loss
e. start-gain
how many different mutation sequence context types are there?
96: 16 sequence contexts (=4x4 different DNA bases for the two positions) and 6 (combining complementary strand sequences) point mutation types → 16 * 6 = 96 mutation sequence context types
missense mutations
mutations in a single nucleotide that results in a substitution of a different amino acid –> a change in the protein encoded
can alter the function of the protein
nonsense mutations
the original amino acid is changed to a stop codon –> results in truncated or nonfunctional protein
what is an example of a nonsense mutation?
TP53 R213: a point mutation in the TP53 gene located on chromosome 17 at position 213 of the protein (7578212th position on Chr 17) where arginine (R) is replaced by a stop codon → causes premature termination of translation process and results in a truncated nonfunctional TP53 protein
stop-loss mutation
the loss of the normal stop codon –> results in abnormal elongation of a protein’s C-terminus until the next stop codon is encountered
start-loss mutation
the start codon (ATG) is lost –> eliminates gene function
start-gain mutation
a point mutation that creates a new start codon (ATG) upstream of the original starting site
if new ATG is CLOSE enough to the original one and in frame, it will be used to initiate translation → adding amino acids to the amino terminus of the original protein
If it is out of frame, it will NOT affect translation of the original protein
generally has low impact on gene function
how many possible numbers of different point mutation types with respect to DNA sequence change?
6 distinct ones: C –> G, C –> A, C –> T, T–> A, T –> C, T –> G
what is the start codon?
ATG
what are the three stop codons?
TAG - UAG
TAA - UAA
TGA - UGA
–> usually codes to Ter
what are the results of insertion and deletions on genes?
a. frameshift mutation that changes the reading frame
b. splice site mutation where splicing usually occurs → would change the transcript so introns could be inserted to mature mRNA molecules
frameshift mutation
changes where translation begins and affects downstream amino acids –> significantly altered or nonfunctional protein
splice site mutation
a mutation at the intron-exon junctions (splice sites) of a gene –> retention of introns and exclusions of exons in mature mRNA –> proteins missing crucial regions or contains nonfunctional sequences
what does an amino acid consist of?
a carboxylic acid group, an amino group, and a side chain (denoted as R)
