Genetic Linkage

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Genetic Linkage

 

the joint transfer of two or more genes from parents to offspring. Genetic linkage occurs because such genes reside on the same chromosome, that is, they belong to the same linkage group and therefore cannot be accidentally recom-bined in meiosis, which occurs in the inheritance of genes residing on different chromosomes.

Genetic linkage was discovered in 1906 by the English geneticists W. Bateson and R. Punnett, who discovered in experiments on the crossing of plants the tendency of some genes to transfer together, thus violating the law of the independent combination of traits. This tendency was correctly explained by T. H. Morgan and his associates, who discovered a similar phenomenon in their study of inherited traits in the fruit fly (Drosophila).

Genetic linkage is measured by the frequency at which crossover gametes or spores are formed by a heterozygote on jointly transferring genes. In these gametes or spores, the genes occur in new combinations rather than in the original combinations, owing to the crossing-over of those parts of the homologous chromosomes bearing the genes. In some bacteria, another measure of genetic linkage is the frequency of joint transmission by inheritance of various genes in conjugation, genetic transformation, and transduction. The extent of genetic linkage may vary among the sexes: it is generally greater in the heterogametic sex. Genetic linkage may even be complete, without crossing-over, in one of the sexes, for example, in male Drosophila or in female Asiatic silkworms (Bombyx morí). The extent of genetic linkage may also vary with the age of the parents and with temperature. In addition, it may vary in the presence of chromosomal rearrangement or of mutant genes that influence the extent of genetic linkage.

S. M. GERSHENZON

References in periodicals archive ?
However, in linked genes, crossing over does occur.
This method of calculating map distance between linked genes using F2 data is an effective method of generating mapping data for students to use in lab.
This method calculates map distances between two linked genes using data generated from the F2 generation of an F1 sibmate cross.
Students will be able not only to determine that two genes are linked to each other using F2 data and chi-square analysis, but also to calculate the map units between linked genes using their F2 data.
Fine structure genetic mapping of the linked genes should be conducted to provide a means for map-based cloning of the wilt resistance genes and studies of their structure and mode of action.
[T.sub.2] and [T.sub.2] testcross progeny in Family 20 confirmed our hypothesis from [T.sub.1] data that RL and 2-5A act as tightly linked genes in this family.
Family 20 was the only transgenic line that did not contain [T.sub.1] progeny in the RL positive/2-5A negative or RL negative/2-5A positive categories, and was determined, by further genetic analyses, to contain tightly linked genes of interest.
This data can be explained by the co-integration of RL and 2-5A, with both transgenes segregating as a single, tightly linked gene cluster.
Genetic analyses of Family 26 indicated that multiple transgenes do not always behave as a stable, tightly linked gene cluster.
The absence of an interchange difference in Dif-62/ Steele [F.sub.1] and suppression of Pc-62 by Pc-38 or a linked gene resulted in 1R:3S segregation in the [F.sub.2] after inoculation with CR181 (Table 2).