Ch. 4

prototroph

wild-type strain of a microorganism

auxotroph

a microbe with one or more mutations

genetic dissection

the use of mutations and recombinants in genetic analyses to identify and assemble the genetic components of biological property or process.

epistatic interaction

a group of specific patterns of gene interaction in which an allele of one gene modifies or prevents the expression or allele or another gene

duplicate gene interaction

a characteristic ratio or phenotypes produced by the interaction of 2 genes that duplicate each other’s action due to genetic redundancy

duplicate gene interaction ratio

15:1

dominant interaction

a characteristic ratio of phenotypes produced by the interaction of 2 genes that control a trait when the presence of dominant alleles or both genes produces one phenotype, one dominant allele of either gene produces a second phenotype, and organisms with one recessive allele for the interacting genes have a third phenotype

dominant interaction ratio

9:6:1

recessive epistasis

a characteristic ratio of phenotypes produced by the interaction of 2 genes that control a trait in which alleles of one gene mask or reduce the expression or alleles of a second gene

recessive epistasis ratio

9:3:4

dominant epistasis

a characteristic ratio or phenotypes produced by the interaction of 2 genes that control a trait in which a dominant allele of one gene mask or reduces the expression of alleles of a second gene

dominant epistasis ratio

12:3:1

dominant suppression

a characteristic ratio of phenotypes produced by the interaction of 2 genes that control a trait in which a dominant allele of one gene suppresses the expression of the dominant allele of the second gene

dominant suppression ratio

13:3

complete penetrance

the observation that the phenotype for a trait is always produced when the corresponding genotype(s) are present

sex-limited traits

a gene or trait expressed exclusively in one sex

sex-influenced traits

a gene, usually autosomal, whose expression differs between males and females of a species

penetrant

expression of the phenotype corresponding to a particular genotype

non penetrant

an organism with a genotype corresponding to a mutant phenotype that instead displays the wild-type phenotype

fully penetrant

an allele that expresses itself in the phenotype every time it is present in the genotype

incomplete penetrance

the occurrence of individual organisms that have a particular genotype or allele but not the corresponding phenotype

Pleiotropy

a single gene mutation that affects multiple and seemingly unconnected properties of an organism

haplosufficient

a wild-type allele that supports wild-type function in the heterozygous organisms. Classified as a dominant wild type allele

haploinsufficient

a wild-type allele that is unable to support wild-type function in a heterozygous genotype. Classified as a recessive wild-type allele

loss-of-function mutation

a mutation that prevents the production of the wild-type protein or renders it inactive. most commonly a recessive mutation

null mutation

a mutation that produced no functional product. most commonly a recessive allele

leaky mutation

a mutation whose phenotype is similar to, but less than, the wild-type phenotype

dominant negative mutation

behaves as a loss-of-function, often due to blocking the formation or normal function of a multimeric protein complex

gain-of-function mutation

a mutation causing a gene to be overexpressed, to be expressed at the wrong time, or to encode a constitutively acting protein; usually inherited as a dominant mutation

hypermorphic

a mutation whose phenotype is similar to, but greater than, the wild-type phenotype

neomorphic

a mutant expressing a new or novel function not seen in the wild-type

wild-type

genotype or phenotype most frequently observed in a natural population for a specific trait.

incomplete dominance

the observation that the phenotype occurring in heterozygous organisms in intermediate between the phenotypes of homozygous organisms but more similar to one homozygous phenotype than to the other

codominance

the equal and detectable expression of both alleles in a heterozygous organism

allelic series

a group of alleles of a gene that displays a hierarchy of dominance relationship among them

temperature sensitive allele

a mutation evident only at or above a certain temperature due to an abnormality of the protein product that affects its stability

lethal mutation

a genetic alteration that leads to the death of the organism

delayed age of onset

the appearance of an abnormal phenotype that is not present at birth but appears later in life and is caused by an inherited mutation

variable expressivity

variation in the degree, magnitude, or intensity of expression of a phenotype

gene-environment interactions

interactions taking place between particular genes and specific environmental factor

gene interaction

referring to genes that interact with one another due to their participation in the production of a particular produce or trait

one gene-one enzyme hypothesis

proposed that each gene encodes a specific protein product and controls a distinct function

genetic heterogeneity

the observation of the same phenotype produced by mutation of any one of 2 or more different genes

genetic complementation analysis

the experimental pairwise comparison of genetic mutations designed to determine whether mutants complement one another by producing wild types

complementation group

a group of mutations that affect the same gene