Terminology - SU 5

Linked genes

Genes located close together on the same chromosome.

Linkage group

A group of linked genes.

Nonrecombinant (parental) gamete

Gamete that contains only the original combinations of alleles that were present in the parents.

Nonrecombinant (parental) progeny

Progeny that possess only the original combinations of alleles that were present in the P generation.

Recombinant gamete

Gamete with new combinations of alleles.

Recombinant progeny

Progeny with new combinations of alleles formed from recombinant gametes.

Recombination frequency

Proportion of recombinant progeny produced in a cross.

Coupling (cis) configuration

Arrangement of linked genes in which wild-type alleles of two or more genes are found on one chromosome, and mutant alleles are on the homologous chromosome.

Repulsion (trans) configuration

Arrangement of two linked genes in which each of a homologous pair of chromosomes contains one wild-type (dominant) allele and one mutant (recessive) allele.

Genic map

Map of the relative distances between genetic loci, markers, or other chromosome regions determined by rates of recombination; measured in recombination frequencies or map units.

Physical map

Map of physical distances between loci, genetic markers, or other chromosome segments; measured in base pairs.

Map unit (m.u.)

Unit of measure for distances on a genetic map; also called a centiMorgan. One map unit equals a 1% recombination frequency.

Two-point testcross

Cross between an individual heterozygous at two loci and an individual homozygous for recessive alleles at those loci.

Three-point testcross

Cross between an individual heterozygous at three loci and an individual homozygous for recessive alleles at those loci.

Interference

Degree to which one crossover interferes with additional crossovers in the same region.

Coefficient of confidence

Ratio of observed double crossovers to expected double crossovers.

Mapping function

Mathematical function that relates recombination frequencies to actual physical distances between genes.

Lod (logarithm of odds) score

Logarithm of the ratio of the probability of obtaining a set of observations, assuming a specified degree of linkage, to the probability of obtaining the same set of observations with independent assortment; used to assess the likelihood of linkage between genes from pedigree data.

Genetic marker

Any variable gene or DNA sequence used to identify a location on a genetic or physical map.

Linkage analysis

Gene mapping based on the detection of physical linkage between genes, as measured by the rate of recombination in the progeny of a cross.

Genome-wide association study

Looks for nonrandom associations between the presence of a trait and alleles at many different loci scattered across a genome—that is, for associations between traits and particular suites of alleles in a population.

Haplotype

A specific set of linked genetic variants or alleles on a single chromosome or on part of a chromosome.

Linkage disequilibrium

Nonrandom association between alleles in a haplotype.

Single-nucleotide polymorphism (SNP)

A site in the genome where individual members of a species differ in a single base pair.

Somatic-cell hybridisation

Fusion of somatic cells of different types. Used for positioning genes on chromosomes.

Cell line

Genetically identical cells that divide indefinitely and can be cultured in the laboratory.

Heterokaryon

Cell possessing two nuclei derived from different cells through cell fusion.

Deletion mapping

Technique for determining the chromosomal location of a gene by studying the association of its phenotype or product with particular chromosome deletions.