Mutation, variants and Polymorphism Flashcards
Where do these alleles come from?
Mutation
What is mutation?
causes either a partial or complete loss of function, but sometimes results in a gain of function,including new functions
Something undersirable or broken and when a variation in DNA sequence originated recently, and is rare in a population
mutation
If a mutation changes the phenotype of an individual, the individual is said to be
Mutant
variants of DNA sequences (and other phenotypes) that co-exist in a population at relatively high frequencies (>1%).
Polymorphism
a difference in DNA sequence that explains whether a person has red hair rather than brown or black hair is an example of
Polymorphism
types of mutation
- Deletion
- substitution
- insertion
Mutations may either occur ____, or may be induced by exposure to _______.
Spontaneously, mutagens
arise from many sources including natural errors in DNA replication, usually associated with base mispairing, or else insertion deletion especially within repetitive sequences.
Spontaneous mutations
Result from mispairing, DNA damage, or sequence interruptions caused by chemical, biological, or physical mutagens.
Induced mutations
By randomly ________, then screening for a ________, it is possible to identify genes associated with specific biological pathways.
inducing mutations, specific phenotype
____________ are dynamic, abundant components of eukaryotic genomes and important forces in evolution.
Transposable elements
limited by silent mutations, redundancy, and embyronic lethality.
The efficiency of mutant screening
Mutation of different genes can produce a similar ________.
phenotype
Complementation testing determines whether two mutants are the result of mutation of the same gene (__________), or if each mutant is caused by mutation of a different gene (_______).
(allelic mutations), (non-allelic mutations).
This ______ causes one or more bases on either strand to be temporarily displaced in a ____ that is not paired with the opposite strand. If this ____ forms on the _________, the bases in the loop may not be ________, and a _______ will be introduced in the growing daughter strand. Conversely, if a region of the daughter strand that has just been ________ becomes displaced in a ______, this region may be ______ again, leading to an ________ of additional sequence in the daughter strand, as compared to the template strand.
strand-slippage, loop, loop, template strand, loop, replicated, deletion, replicated, loop, replicated, insertion
Mispairing of bases (e.g. G with T) can occur due to
- tautomerism
- alkylating agents
- or other effects.
occur occasionally during replication, especially in regions with short, repeated sequences. This can lead to either deletion (left) or insertion (right) of sequences compared to the products of normal replication (center), depending on whether the template strand or daughter strand “loops-out” during replication.
Strand-slippage
Thus regions with ____ are tend to be highly polymorphic, and are thereforecparticularly useful in genetics. They are called
short-sequence repeats
(SSRs), microsatellites
may disrupt the coding or regulatory sequence of a gene, including the fusion of part of one gene with another.
insertion
insertions can occur spontaneously, or they may also be intentionally stimulated in the laboratory as a method of mutagenesis called
transposon-tagging
an insertional element modified from a bacterial pathogen, is used as a mutagen in some plant species.
T-DNA
Transposable elements (TEs) are also known as
mobile genetic elements, or more informally as jumping genes.
They are present throughout the chromosomes of almost all organisms. These DNA sequences have a unique ability to be cut or copied from their original location and inserted into new locations in the genome.
Transposable elements
New location in the genome is called
transposition
Be inserted into almost any region of the genome and can therefore insert into genes, disrupting its function and causing a mutation
tranposable elements
element of class I
retrotransposons
element of class II
transposons
enzyme in class I
integrase
enzyme of class II
transposase
these transpose by means of an RNA intermediate
retrotransposons
They do not use reverse transcriptase or an RNA intermediate for transposition
transposons
The TE transcript is reverse transcribed into DNA before being inserted elsewhere in the genome through the action of
enzymes like integrase
cut DNA from the original location and then this excised dsDNA fragment is inserted into a new location.
transposase
can only transpose if they are supplied with enzymes produced by other
non-autonomous TEs
True or false. In all cases, enzymes for transposition recognize conserved nucleotide sequences within the TE, which dictate where the enzymes begin cutting or copying.
True
located elsewhere in the genome.
autonomous TEs
True or false. The human genome consists of nearly 45% SEs
False, TEs
the vast majority of which are families of Class I elements called _____ and ______.
LINEs, SINEs
True or false. The short, Alu type of LINE occurs in more than one million copies in the human genome (compare this to the approximately 21,000, non-TE, protein-coding genes in humans)
False, Sine
True or false TEs make up a significant portion of the genomes of almost all prokaryotes
False, eukaryotes
Class I element mechanism
copy-and-paste
Class II element mechanism
cut-and-paste
Even the cut-paste mechanism can lead to an decrease in TE copy number.
False, increase
they may disrupt gene function by insertion into a gene’s coding region or regulatory region
TEs
are sometimes mistakenly transposed along with the TE; this can lead to gene duplication.
adjacent regions of chromosomal DNA
true or false. The breakage of strands by TE excision and integration can disrupt genes, and can lead to chromosome rearrangement or deletion if errors are made during strand rejoining.
True
True or false. Having so many similar TE sequences distributed throughout a chromosome sometimes allows pairing of regions of homologous chromosomes at meiosis, which can cause equal crossing-over, resulting in deletion or duplication of large segments of chromosomes.
False, mispairing, unequal
junk DNA
TEs before
