Chapter 18 Part 1 Flashcards
Mutation
Inherited change in the DNA sequence
Extra: They are essential to the study of genetics and are useful in many other biological fields
Somatic Mutation
Mutations in somatic tissues – not the reproductive organs like the ovary and testes
Mutations are passed on by mitosis, and can produce clones of this mutation
This type of mutation is known to increase with age
Germ-line Mutation
Mutations – in the gametes or reproductive tissues
This type of mutation can be passed on to future generations, producing offspring that carry that mutation in all their somatic and germ-line cells
Gene Mutation
Mutation that affects a single gene or locus
Spontaneous Mutations
Mutations that arise from natural changes in DNA structure or from error of replication
Induced Mutation
Those mutations that arouse from changes caused by environmental chemicals or radiation
Tautomeric Shift
The positions of protons – hydrogen atoms – in DNA bases change
“Each of the four DNA bases are in dynamic equilibrium, although one form is much more common than the other”
Cytosine rare form can bind with Adenine common form
Thymine common form can bind with Guanine rare form
Wobble –Mis-pairing
The normal protonated form of the nitrogenous bases are able to pair because of flexibility in the DNA helical structure
Thymine can wobble with Guanine
Cytosine can wobble with Adenine
Incorporates Errors
When a base substitution causes a mis-paired base to be incorporates into a newly synthesized nucleotide chain
- DNA Wild Type
TTCG
AAGC - The DNA strands separate for DNA replication
TTCG Thymine on the original strand pairs with Guanine through wobble
AGGC –> Incorporated errorTTCG –> wild type
AAGC - At the end of the next round of replication, the guanosine nucleotide pairs with cytosine, leading to a transition mutation
TTCG –> Wild type
AAGC
TCCG –> Mutant
AGGC
Replicated Error
The permanent base pair mutation that aroused because of an incorporated mistake
Stand Slippage
Small insertions and deletions can arise spontaneously in crossing over and replication
Slipping of the template and newly synthesized strands in replication in which one of the strands loops out from the other and nucleotides are inserted or deleted on the newly synthesized strand
The shorter strand that loops out has an insertion
The longer strand that loops out will have a deletion
Misaligned pairing
If homologous chromosomes misalign during cross over, one crossover products contains an insertion and the other contains a deletion
Depurination
The loss of a purine base from a nucleotide
Depurination results when the covalent bond connecting the purines to the 1’-carbon atom the deoxyribose sugar breaks, producing an apuritic site
In the absence of base-pairing constraints, an incorrect nucleotide – most often adenine – is incorporated into the newly synthesized DNA strand opposite to the apuritic site… leading to incorporated errors
Deamination
The loss of an amino group – NH2 – from a base
Ex…Cytosine can be converted to uracil
A form of Transition mutation
Ex….
5mC –> Thymine
Mutagen
Any environmental agent that significantly increases the rate of mutation above the spontaneous rate is called a mutagen
Transition Mutations
A purine changes to a purine
A pyrimidine changes to a pyrimidine
Transversion
A purine changes to a pyrimidine
A pyrimidine changes to a purine
Base Analogs
Chemicals with structure similar to those of any of the four stranded nitrogenous bases of DNA
DNA polymerase cannot distinguish these analogs from the stranded bases, so if base analogs are present during replication, they may be incorporates into newly synthesized DNA molecules
For example…5-bromouracil is an analog of thymine – it has the same structure as thymine except that it has a broken – Br atom on the 5-carbon atom instead of a methyl group… so instead of pairing with adenine…it pairs with guanine
Same thing can happen with 2-aminopurine which is analog to Adenine, which pairs wrongly with cytosine
Pyrimidine dimers
Pyrimidine bases readily absorb UV light, which causes chemical bonds to form between adjacent pyrimidine molecules on the same strand of DNA, creating pyrimidine dimers
SOS system
overcome blocks caused by pyrimidine dimers
Carcinogen
cancer-causing substances
Ames Test
Is based on the principle that both cancer and mutations results from damage to the DNA –> a solution to help resolve cancer
Transposable Elements
DNA sequence capable of moving from one site to another within the genome through a mechanism that differs from that of homologous recombination – are often a cause of mutations
Suppressor Mutation
A mutation that hides or suppresses the effect of another mutation
“A suppressor mutation is a second mutation that alleviates or reverts the phenotypic effects of an already existing mutation in a process defined synthetic rescue” - https://en.wikipedia.org/wiki/Suppressor_mutation
–> Let us say that a mutation cause the amino acid arginine to change to serine
–> Let us say that another mutation – suppressor mutant – changes serine to lysine
Since lysine and arginine share similar properties –> the mutant these type has no effect on the gene or the phenotype
Intragenic
Suppressor mutations on the same genes as original mutation
Intergenic
Suppressor mutations on a different gene as the original mutation
In-frame mutations
An insertion or a deletion that alter the reading frame and may change many codons
–> multiples of 3
Loss-of-functional mutation
Partial or complete absence of gene product function
usually recessive – requires two copies in a diploid organism to see a phenotype
Gain-of-functional mutation
Gene product has a new function
Usually dominant – one copy – in a diploid organism – produces a phenotype
Conditional Mutation
Phenotype seen under certain conditions
– elevated temperatures
Lethal mutation
Causes premature death
