4 Flashcards
haplosufficient
Dominant wild-type alleles are identified as haplosufficient since only one copy is sufficient to produce the wild-type phenotype.
haploinsufficient
a single copy of the Allele is not sufficient to produce the wild-type phenotype
loss of function mutation
a mutation that results in a significant decrease or in the complete loss of the functional activity of a gene product.
Usually recessive, but some times dominant
gain of function mutation
identify alleles that have acquired a new function or are altered to express substantially more activity than the wild-type allele.
- almost always dominant
- some are lethal in a homozygous state
null mutation
amorphic mutation
a loss of function mutation that results in a complete loss of gene function in comparison to the wild-type allele
leak mutation
hypomorphic mutation
a mutation resulting in the partial loss of gene function.
-can lead to dominant loss of function mutations
Hypermorphic mutations
produce more gene acivity per allele than the wild type
- usually dominant
- usually resulting from mutations that lead to more of the protein with increased function resulting from the mutation. as opposed to a mutation changing the amino acid configuration on the protein itself
neomorphic mutations
mutations that acquire novel gene activities not found in the wild type and are usually dominant. The gene products of neomorphic mutants are functional, but have structures that differ from the wild-type gene product, leading to a mutant protein that functions differently than the wild-type protein.
specific taxonomic genetic nomenclature
see back of book cover page
Inomplete dominance (partial dominance)
identifies circumstances when dominance of one allele over another is incomplete.
- more common than complete dominance
- the phenotype of the heterozygous organism is distinctive, falling between the categories of homozygous mutant and homozygous wild-type.
Codominance
leads to a heterozygous phenotype different from the phenotype of either homozygous parent.
differs from incomplete dominance in how it is characterized by the detectable expression of both alleles in heterozygotes.
most clearly identified when the protein products of both alleles are detectable in heterozygous organisms, typically by means of some sort of molecular analysis such as gel electrophoresis or a biochemical assay that can distinguish between the different proteins.
allelic series
in populations with multiple alleles, an order of dominance emerges among the alleles, based on the activity of each allele’s protein product, forming a sequential series known as an allelic series.
temperature-sensitive allele
an allele producing a protein that is temperature sensitive, usually meaning that it denatures at high levels of heat
c^h is an example of this because it creates a pigment making enzyme that is temperature sensitive, so it only works in areas of the organism farther away from its core, where it is the hottest. thus, the phenotypic expression of this gene is characterized by the presence of pigment in the extremities and with no pigment in the areas seperate from the extremities
lethal mutation
a single-gene mutation thats so messed up that they cause death early in life or terminate gestational development.
-often recessive, because natural selection kills off any dominant lethal mutations pretty quickly
sex-limited gene expression
the limitation of gene expression to one sex but not the other
sex limited traits
traits only evident in a particular sex. they are result of sex-limited gene expression
sex-influenced traits
traits in which the phenotype corresponding to a particular genotype differs depending on the sex of the organism carrying the genotype
Hormones are thought to influence the differential expression of genotypes in the sexes
delayed age of onset
abnormalities produced by a particular gene disfunction do not appear until after the affected organisms have had an opportunity to reproduce and transmit the mutation to the next generation
ex: huntingtons
penetrant
when the phenotype of an organism is consistent with the organisms genotype, the organism is said to be penetrant for the trait. In such a case, if the organism carries a dominant allele for the trait in question, the dominant phenotype is displayed.
nonpenetrant
an organism with a particular genotype that fails to produce the corresponding phenotype is nonpenetrant for the trait
incomplete penetrance
traits for which nonpenetrant individuals occasionally or routinely occur are identified as displaying incomplete penetrance.
variable expressivity
in this phenomenon, the same genotype produces phenotypes that vary in the degree or magnitude of expression of the allele of interest
what are the three kinds of interactions that may be responsible for incomplete penetrance or variable expressivity
1) other genes that act in ways that modify the expression of the mutant allele
2) environmental or developmental (i.e., nongenetic) factors that interact with the mutant allele to modify its expression
3) some combination of other genes and environmental factors interacting to modify expression of the mutation
pleiotropy
the alteration of multiple, distinct traits of an organism by a mutation in a single gene.
Most mutations displaying pleiotropy do so by either altering the development of phenotypic features through the direct action of the mutant protein or as a secondary result of a cascade of problems stemming from the mutation
gene interaction
the collaboration of multiple genes in the production of a single phenotypic character or a group of related characteristics
biosynthetic pathway
networks of interacting genes that produce a molecule or compound as their end product.
one gene - one enzyme hypothesis
says that each gene produces an enzyme, and each enzyme has a specific functional role in the biosynthetic pathway that produces a phenotype.
genetic dissection
for biosynthetic pathways
an experimental approach that tests the ability of a mutant to execute each step of a biosynthetic pathway and assembles the steps of a pathway by determining the point at which the pathway is blocked in each mutant.
epistasis
the name given to gene interactions - called epistatic interactions - in which an allele of one gene modifies or prevents the expression of alleles at another gene. The genes that interact by epistasis are involved in producing a particular phenotypic characteristic, and they usually participate in the same pathway.
Epistasis is most readily detected among progeny of dihybrid crosses where bot genes carry dominant and recessive alleles.
epistatic ratios
look into them further. page 127
complementary gene interaction
results in a 9:7 phenotypic ratio
requires genes to work in tandem to produce a single product
genetic complementation
the ability of two mutants with the same mutant phenotype to produce progeny with the wild-type phenotype is called genetic complementation
indicates that more than one gene is involved in determining the phenotype
duplicate gene action
the genes in a redundant system have this.
they either encode the same gene product, or they encode gene products that have the same effect in a single pathway or compensatory pathways
dominant interaction
characterized by a 9:6:1 ratio of phenotypes in the progeny of a dihybrid cross
recessive epistasis
homozygosity for a recessive allele at one locus can mask the phenotypic expression of a second gene
has a characteristic 9:3:4 ratiof
examples from this chapter
go over them and create seperate set of slides
dominant epistasis
a dominant allele at one locus masks the expression of alleles at a second locus
has a characteristic 12:3:1 ratio
dominant suppression
similar to dominant epistasis but occurs when a dominant allele of one gene completely suppresses the phenotypic expression of alleles of another gene
genetic heterogeneity
when mutations of different genes can produce the same, or very similar, abnormal phenotypes
complementation group
mutations that mutually fail to complement one another are identified as this. Consisting of one or more mutant alleles of a single gene.
consists of mutants whose phenotypes consistently fail to complement one another and that complement in other complementation groups.
