Genetic distance

Twenty populations were sampled with plants from Hailuoto, at 65°00 N, representing the northernmost site and material from Hanko, at 59°49 N, representing the southernmost collection site (and, incidentally, the southernmost point of land in the country). Five samples represented central Finland with the remainder originating from the southern part. Fifty-five compounds were detected by GC-MS analysis, 53 of which were identified. The data obtained were subjected to complete linkage analysis, which differentiated several clusters that corresponded moderately well with geography. Genetic distance values derived from the RAPD data correlated well with chemical distance values determined from the terpene data (r=0.41, P<0.0001). 

Average Difference in Genetic Distance (A) between Ordered and Disordered Regions of 26 Protein Families a... 

A universal tree of life has been derived from this analysis (Figure 9.10) for all species alive on Earth today that enables a genetic distance to be determined between species but not necessarily a historical distance. 

Universal tree of life The categorisation of species on Earth due to its genetic material producing a genetic distance from a common genetic ancestor. 

The recombination frequency provides a measure of the genetic distance between any pair of linked loci. Genetic distances are often expressed in centiMorgans (cM). One centiMorgan is equal to a 1% recombination frequency between two loci (for example, two loci that are 10 cM apart would have a recombination frequency of 10%). Physically, 1 cM is approximately equal to 1 million base pairs of DNA (1 Mb). This relationship is only approximate, however, because crossover frequencies vary somewhat throughout the genome (e.g., crossovers are less common near centromeres and more common near telomeres). 

These authors tested 120 allele frequencies in 42 human populations. They calculated from these measurements genetic distances between the populations and estimated the times of their separation. They summarized their data, and thus constructed nine population clusters (Fig. 1). The greatest differences were between African and all non-African populations, in support of the theory that all present human beings derived from a wave of emigrants who left Africa approximately 100,000 years ago. 

Figure 1 Linkage Tree. Analysis of nine population clusters, condensed from data obtained by studying 42 populations. The genetic distance 0.2 represents approximately 150,000 years. Source Figure 2.3.3 from Ref. 12.

Genetic Distance and Divergence Times Based on 383 Fibroblast Proteins"... 

Centimorgan A measure of genetic distance that tells how far apart physically two genes are, based on the frequency of recombination or crossover between the two gene loci. A frequency of 1% recombination in meiosis is 1 centimorgan and equals about 1 million base pairs. See Southern, E.M., Rrospects for a... 

Where genetic testing is based on linked genetic markers, the report should indicate the false-negative and falsepositive rates arising from recombination between the test locus and the disease locus. This can be inferred from the known genetic distance between the loci. 

Figure 41-2 Map of the human MHC region.The organization of the most important class i and class li genes of the MHC is shown, with approximate genetic distances given in thousands of base pairs (kb). Genes are ordered from telomere to centromere. Not shown are MHC class ill genes, which map between class I and class II genes. (See Color Plate 12.)...

Fig. 4 Genetic relatedness between HEV strains from human and non-human sources and from various countries. Minimal spanning trees of 81 sequences of 148 nucleotides HEV RNA showing genetic distances between genotype three HEV strains from humans and animals, (a) Strains labelled by geographical origin, (b) Strains labelled by biological origin. The 13 recent Dutch cases are marked with ID numbers inside the coloured circles (adapted from Bergen et al. BMC Infectious Diseases 2008 8 61 doi 10.1186/1471-2334-8-61)...

When genetic data are available from several populations, it is natural to ask, how genetically similar are the populations In general, genetic distance is considered as related to the time since the population diverged from a single... 

The simplest method for developing a genetic distance matrix is the average distance method or UPGMA (58). This method is used not only to construct a phenogram, but it can also be used to construct a phylogenetic tree. In UPGMA, a measure of evolutionary distance is computed for all pairs of... 

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