Complete linkage

For the clustering method, see Complete-linkage clustering

Linkage

Genetic Linkage is the tendency of alleles, which are located closely together on a chromosome, to be inherited together during the process of meiosis in sexually reproducing organisms. During the process of meiosis, homologous chromosomes pair up, and can exchange corresponding sections of DNA. As a result, genes that were originally on the same chromosome can finish up on different chromosomes. This process is known as genetic recombination. The rate of recombination of two discrete loci corresponds to their physical proximity. Alleles that are closer together have lower rates of recombination than those that are located far apart.The distance between two alleles on a chromosome can be determined by calculating the percentage or recombination between two loci. These probabilities of recombination can be used to construct a linkage map, or a graphical representation of the location of genes and gene in respect to one another. If linkage is complete, there should be no recombination events that separate the two alleles, and therefore only parental combinations of alleles should be observed in offspring. Linkage between two loci can have significant implications regarding the inheritance of certain types of diseases.[1]

Gene maps or Qualitative Trait Loci (QTL) maps can be produced using two separate methods. One way uses the frequency of marker alleles and compares them to individuals selected from the two tails of the trait distribution. This is called the Trait-Based approach and strictly uses phenotypic information only to select the individuals for a sample. The other approach is called the Marker-Base approach (MB), and uses both the difference in marker allele frequencies and the phenotypic values of each marker genotype when selecting samples.[2]

(Click here for more information on Linkage Maps)

Complete Linkage

In genetics Complete Linkage is defines as the state in which two loci are so close together that alleles of these loci are virtually never separated by crossing over. The closer the physical location of two genes on the DNA, the less likely they are to be separated. In case of Drosophila and female Silkworms, where there is complete absence of recombinant types due to absence of crossing over.

Economic Benefits

Being able to determine linkage between genes can also have major economic benefits. Learning about linkage of traits in sugar cane has lead to more productive and lucrative growth of the crop. Sugar cane is a sustainable crop that is one of the most economically viable renewable energy sources. QTL analysis for sugarcane was used to construct a linkage map that identified gene clusters and important linked loci that can be used to predict the response to fungal infection in a specific line of sugar cane.[3]

Medical Benefits

Linkage mapping can also be useful in determining the inheritance patterns of traits such as psychological disease. Linkage studies of panic disorder and anxiety disorders have indicated regions of interest on specific chromosomes. Chromosomes 4q21 and 7p are being considered strong candidate regions for panic and fear-associated anxiety disorder loci. Knowing the specific location of these loci and their probability of being inherited together based on their linkage can offer insight into how these disorders are passed down, and why they often occur together in patients.[4]

References

  1. ↑ Single, Richard M.; Strayer, Nick; Thomson, Glenys; Paunic, Vanja; Albrecht, Mark; Maiers, Martin (2015-09-07). "Asymmetric linkage disequilibrium: Tools for assessing multiallelic LD". Human Immunology. doi:10.1016/j.humimm.2015.09.001. ISSN 1879-1166. PMID 26359129.
  2. ↑ Tenesa, Albert; Visscher, Peter M.; Carothers, Andrew D.; Knott, Sara A. (2005-03-01). "Mapping quantitative trait loci using linkage disequilibrium: marker- versus trait-based methods". Behavior Genetics 35 (2): 219–228. doi:10.1007/s10519-004-0811-5. ISSN 0001-8244. PMID 15685434.
  3. ↑ Palhares, Alessandra C.; Rodrigues-Morais, Taislene B.; Van Sluys, Marie-Anne; Domingues, Douglas S.; Maccheroni, Walter; Jordão, Hamilton; Souza, Anete P.; Marconi, Thiago G.; Mollinari, Marcelo (2012-01-01). "A novel linkage map of sugarcane with evidence for clustering of retrotransposon-based markers". BMC genetics 13: 51. doi:10.1186/1471-2156-13-51. ISSN 1471-2156. PMC 3443450. PMID 22742069.
  4. ↑ Logue, Mark W.; Bauver, Sarah R.; Knowles, James A.; Gameroff, Marc J.; Weissman, Myrna M.; Crowe, Raymond R.; Fyer, Abby J.; Hamilton, Steven P. (2012-04-01). "Multivariate analysis of anxiety disorders yields further evidence of linkage to chromosomes 4q21 and 7p in panic disorder families". American Journal of Medical Genetics. Part B, Neuropsychiatric Genetics: The Official Publication of the International Society of Psychiatric Genetics 159B (3): 274–280. doi:10.1002/ajmg.b.32024. ISSN 1552-485X. PMC 3306232. PMID 22253211.
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