Topic 3 Genetics terms

allelic series

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

biosynthetic pathway

a multistep biochemical pathway that synthesizes an end product or compound

codominance

A condition in which neither of two alleles of a gene is dominant or recessive; both contribute to the phenotype

complementation analysis

allows the determination of whether two mutations yielding similar phenotypes are on the same gene or on separate genes

complementation group

a group of mutations that affect the same gene

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

dominant negative mutation

Exerts a dominant effect. A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning

Epistasis

A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.

gain of function mutation

causes the appearance of a new trait or function or causes the appearance of a trait in inappropriate tissue or at an inappropriate time

gene interaction

interaction between genes at different loci that affect the same characteristic

gene-environment interaction

situation in which the effects of genes depend on the environment in which they are expressed

genetic complementation

production of wild-type progeny when recessive mutations in two different genes are combined

genetic dissection

The use of recombination and mutation to piece together the various components of a given biological function.

genetic heterogeneity

a phenotype that can be caused by variants of any of several genes

Haploinsuffient

-a single copy (haplo) is insufficient to produce the wild-type phenotype in the heterozygous genotype

hypermorphic mutation

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

hypomorphic (leaky) mutation

reduced gene expression or activity of a product

(e.g. replacement impairs protein function but doesn't eliminate it, reduced transcription)

(effects on gene function)

incomplete/partial dominance

expressing a heterozygous phenotype that is distinct from the phenotype of either homozygous parent

lethal mutation

a gene or chromosomal mutation that influences the development of an organism in such a way that the organism cannot survive

loss of function mutation

Causes the complete or partial absence of normal function.

neomorphic mutation

generate gene product with new function or that is expressed at inappropriate time or place

null mutation

a mutation that results in complete absence of function for the gene

Penetrance

The percentage of individuals with a particular genotype that actually displays the phenotype associated with the genotype.

incomplete penetrance

Not all individuals with a mutant genotype show the mutant phenotype

Pleiotropy

A single gene having multiple effects on an individuals phenotype

sex-influenced trait

an autosomal trait that is influenced by the presence of male or female sex hormones

sex-limited traits

a characteristic controlled by autosomal genes that is phenotypically exhibited in only one of the two sexes.

temperature-sensitive mutation/allele

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

variable expressivity

individuals with the same genotype have related phenotypes that vary in intensity

complementary gene interaction pathway

9:7

duplicate gene interaction pathway

15:1

dominant gene interaction pathway

9:6:1

recessive epistasis gene interaction pathway

9:3:4

dominant epistasis gene interaction pathway

12:3:1

dominant suppression gene interaction pathway

13:3

allelic phase

the arrangements of alleles of linked genes on homologous copies of a chromosome pair

coefficient of coincidence

ratio of observed double crossovers to expected double crossovers

double recombinant (double crossover)

The occurrence of two crossovers between homologous chromosomes in a particular region. May involve two, three, or all four chromatids.

first division segregation

when the two alleles of a gene are segregated into different cells at the first meiotic division

genetic linkage

tendency for genes located close together on the same chromosome to be inherited together

Haplotype

A group of alleles of different genes on a single chromosome that are closely enough linked to be inherited usually as a unit

genetic interference

The phenomenon where one cross over event may prevent subsequent events in nearby regions.

intragenic recombination

Recombination within a gene.

linkage disequilibrium

When a pair of alleles from two loci are inherited together in the same gamete more/less often than random chance would expect

linkage group

Alleles of different genes that are located on the same chromosome and tend to be inherited together

LOD score

statistical value representing the probability of genetic linkage between the genes

mapping function

Relates recombination frequencies to actual physical distances between genes

map unit (m.u.)

Unit of measure for distances on a genetic map; 1 map unit equals 1% recombination.

Centimorgan (cM)

(also, map unit) relative distance that corresponds to a recombination frequency of 0.01

parental chromosomes (nonrecombinant chromosomes)

Chromosomes in gametes produced when crossing over does not take place between linked genes. Alleles marking each gene are retained in their initial (parental) configurations.

recombinant chromosome

Chromosomes that combine genes from both parents due to crossing-over

recombination frequency

With respect to two given genes, the number of recombinant progeny from a mating divided by the total number of progeny. Recombinant progeny carry combinations of alleles different from those in either of the parents as a result of independent assortment of chromosomes or crossing over.

second-division segregation

Different alleles go into different nuclei at the second meiotic division producing an MII division pattern of ascospores

syntenic genes

genes located on the same chromosome

Tetrad

structure containing four chromatids that forms during meiosis

tetrad analysis

The analysis of genetic linkage by analysis of different tetrad segregation types.

theta value

A variable indicating a recombination distance between genes. Used in lod score analysis.

three-point test-cross analysis

A test cross designed to identify genetic linkage between three genes and to provide data for determination of recombination frequency between linked genes.