Genetic screening for mutations- Forward genetics Flashcards
a process that identifies genes that affect biological processes by introducing random mutations into a population and then looking for mutants with specific phenotypes.
Mutant screening
The ________ is defined as the gametes and any of their developmental precursors, and is therefore distinct from the ________ (i.e. non-reproductive cells) of the body.
germline, somatic cells
Because most induced mutations are recessive, the progeny of mutagenized individuals must be mated in a way that allows the new mutations to become
homozygous (or hemizygous)
These alleles are due to changes in the DNA sequence that cause it to no longer produce the same level of active protein as the wild-type allele.
loss-of-function allele
alleles tend to be recessive because the wild-type allele is haplosufficient
loss-of-function allele
loss-of-function allele that produces no active protein
amorph or null
alleles with only a partial loss-of-function
hypomorphic
More rarely, a mutant allele may have a gain-of-function, producing either more of the active protein
hypermoprh
producing an active protein with a new function
neomorph
alleles have an activity that is dominant and opposite to the wild-type function; also known as dominant negative mutations.
antimorph
5 types of mutant allele
(1) amorph, (2) hypomorph, (3) hypermorph, (4) neomorph, and (5) antimorph.
They make no active product – zero function.
amorph
The absence of function in amorph can be due to a lack of ______ or due to the __________
transcription (gene regulation mutation), production of a malfunctioning (protein coding mutation) product
They make an incompletely functioning product.
Hypomorph
Hypomorph could occur via ____ or via the production of a _______.
reduced transcription, product that lacks complete activity
Hypomorph alleles are sometimes referred to as ________, because they provide some function, but not complete function.
Leaky mutations
True or false. Both amorphs and hypomorphs tend to be dominant to wild type because the wild type allele is usually able to supply sufficient product to produce a wild type phenotype called ______
False. recessive, haplo-sufficient
________ alleles are almost always dominant to the wild type allele.
Gain-of-funtion
Hypermorph can occur via ______ or by changing the product to make it more efficient/effective at its function.
increased transcription
It can be either new expression (new tissue or time) or a mutation in the product to create a new function (additional substrate or new binding site), not present in the wild type product.
Neomorph
These alleles usually have no normal function of their own and they interfere with the function from the wild type allele.
Antimorph
also known as dominant negative mutations.
antimorph
All mutations can be sorted into one of the five morphs base on how they behave when heterozygous with other alleles – deletion alleles (zero function), wild type alleles (normal function), and duplication alleles (double normal function).
Identifying Muller’s Morphs
deletion alleles function
zero function
wild type alleles function
normal function
duplicated alleles function
double normal function
True or false. After mutagen treatment, the vast majority of base pair changes (especially substitutions) have effect on the phenotype.
False, no effect
When the mutagen treatement happened, majority of base pair changes have no effect on te phenotype, this is because?
the change occurs in the DNA sequence of a non-coding region of the DNA, such as in inter-genic regions (between genes) or within an intron region.
Also, even if the change occurs in a base within a codon, it may not change the amino acid that it encodes (recall that the genetic code is degenerate; for example, GCT, GCC, GCA, and GCG all encode alanine) and is referred to as a _______.
Silent mutation
True or false. The base substitution may change an amino acid, but this doesn’t alter the function of the product, so phenotypic change would occur.
False, no phenotypic
Give the 4 reasons why some mutations may not have detectable phenotypes
- Silent changes
- Environment and genetic redundancy
- Essential genes and lethal alleles
- Naming genes
True of false. There are also situations where a mutation can cause a complete gain-of-function of a gene, yet not produce a change in the phenotype, even when the mutant allele is homozygous. The phenotypic change can be due to environmental effects: the loss of that gene product may not be apparent in that environment, but might in another.
False. loss-of-function of a gene, lack of a phenotypic change
The encoding of similarly functioning genes at more than one locus in the genome.
genetic redundancy
True or false. genes with redundant functions can be easily identified by mutant screening.
False,cannot be
Mutations in essential genes create ___________ that arrest the development of an individual at an __________. This type of mutation may therefore go unnoticed in a typical mutant screen because they are absent from the progeny being screened
recessive lethal alleles, embryonic stage
true or false. The progeny of a dihybrid cross involving an embryonic lethal recessive allele may therefore all be of a single phenotypic class, giving a phenotypic ratio of 1:0 (which is the same as 3:0). In this case the mutation may not be detected.
false, monohybrid
True or false. Many genes have been first identified in mutant screens, and so they tend to be named after their mutant phenotypes, not the normal function or phenotype.
True
For mutations to be used in complementation tests they are?
(1) usually true-breeding (homozygous at the mutant locus), and (2) must be recessive mutations.
True or false. Dominant mutation can be used in complementation tests.
False, cannot
True or false. Some mutant strains may have more than one gene locus mutated and thus would fail to complement mutants from more than one other locus (or group)
True
______ is one of many diseases that geneticists have shown to be caused by mutation of a single, well-characterized gene. _______ is the most common (1/2,500) life-limiting autosomal recessive disease among people of European heritage, with ~ 1 in 25 people being carriers.
Cystric fibrosis (CF)
Fail to complement means
allelic mutation
can complement means
non-allelic mutation
Cystric fibrosis is due to a mutation in the________, which was identified by Lap-chee Tsui’s group at the University of Toronto.
CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) gene
Epithelial tissues in some organs rely on the CFTR protein to transport ions (especially Cl-) across their cell membranes. The passage of ions through a six-sided channel is gated by another part of the CFTR protein, which binds to _____.
ATP
In the lungs, insufficient CFTR means…..
this causes mucus to accumulate and can lead to infection
Defects in CFTR affects what of the following parts of the body?
pancreas, liver, intestines, and sweat glands, all of which need this ion transport.
True or false. CFTR is also expressed at high levels in the salivary gland and bladder, but defects in CFTR function do not cause problems in these organs, probably because other ion transporters are able to compensate.
true
CFTR allele among CF patients is called
ΔF508 (delta-F508; or PHE508DEL)
a deletion of three nucleotides that eliminates a phenylalanine from position 508 of the 1480 aa wild-type protein.
ΔF508 (delta-F508; or PHE508DEL)
Mutation _____ causes CFTR to be folded improperly in the endoplasmic reticulum (ER), which prevents CFTR from reaching the cell membrane.
ΔF508 (delta-F508; or PHE508DEL)
_______ is effective on only some CFTR mutations, most notably G551D
Kalydeco
where glycine is substituted by aspartic acid at position 551 of the protein; GLY551ASP
G551D
The _______ mutation affects the ability of ATP to bind to CFTR and open the channel it for transport.
G551D
______ compensates for mutation by binding to CFTR and holding it in an open conformation.
Kalydeco
