Impact of Natural Selection Due to Malarial Disease on Human Genetic Variation

Species populations commonly carry a great deal of genetic variation which is not expressed in individual phenotypes. Cryptic variation can be carried in recessive alleles, in cases of heterosis, or where modifier genes inhibit expression of the hidden trait. Other genetic and ecological factors also allow cryptic variation. Stabilizing selection prevents the expression of hidden traits; normalizing selection weeds out the deviants and canalizing selection suppresses their traits. Together the two keep the species near the top of the adaptive peak. Cryptic variation balances a species' need to be well-adapted to its environment and also for it to maintain a reserve of variation for potential environmental change. Expression of cryptic traits is rare and is usually associated with times of greatly reduced natural selection and rapid population growth, when the lower slopes of the adaptive peak are exposed.A possible example of the manifestation of cryptic traits occurs within the lower Trentonian Rafinesquina lineage of New York State. The two most commonly reported species of the genus have been reappraised in terms of cryptic variation. Extensive collections of Rafinesquina “lennoxensis” reveal far more intergrading morphotypes than had hitherto been recognized. The form which Salmon (1942) described is broadly U-shaped with sulcate margins. It grades into very convex forms as well as sharply-defined or convexly geniculate types. Of great importance, all forms grade into the flat, U-shaped, alate R. trentonensis, which is, by far, the most common and widespread lower Trentonian member of the genus. The R. “lennoxensis” assemblage has a very narrow biostratigraphy, being confined to a few locations in the upper Napanee Limestone. This places it in a quiet, protected, low stress, lagoonal setting behind the barrier shoal facies of the Kings Falls Limestone.The R. “lennoxensis” assemblage does not constitute a natural biologic species; it is reinterpreted as an assemblage of phenodeviants occupying a low stress, low natural selection lagoon facies. All such forms should be included within R. trentonensis. Given the evolutionary plasticity of this genus, extensive cryptic variation is not surprising.

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Evolution and evolvability: celebrating Darwin 200

Biology Letters ◽

10.1098/rsbl.2008.0639 ◽

2008 ◽

Vol 5 (1) ◽

pp. 44-46 ◽

Cited By ~ 33

Author(s):

John F.Y Brookfield

Keyword(s):

Genetic Variation ◽

Natural Selection ◽

Time Scales ◽

Evolutionary Change ◽

Adaptive Mutation ◽

Genetic Covariances ◽

The Relationship ◽

The Way

The concept of ‘evolvability’ is increasingly coming to dominate considerations of evolutionary change. There are, however, a number of different interpretations that have been put on the idea of evolvability, differing in the time scales over which the concept is applied. For some, evolvability characterizes the potential for future adaptive mutation and evolution. Others use evolvability to capture the nature of genetic variation as it exists in populations, particularly in terms of the genetic covariances between traits. In the latter use of the term, the applicability of the idea of evolvability as a measure of population's capacity to respond to natural selection rests on one, but not the only, view of the way in which we should envisage the process of natural selection. Perhaps the most potentially confusing aspects of the concept of evolvability are seen in the relationship between evolvability and robustness.

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The genomics of adaptation

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2012.2322 ◽

2012 ◽

Vol 279 (1749) ◽

pp. 5024-5028 ◽

Cited By ~ 35

Author(s):

Jacek Radwan ◽

Wiesław Babik

Keyword(s):

Genetic Variation ◽

Natural Selection ◽

Royal Society ◽

Genetic Basis ◽

Genomic Data ◽

Evolutionary Change ◽

Introductory Article ◽

Technological Advances ◽

A Genome ◽

Genome Level

The amount and nature of genetic variation available to natural selection affect the rate, course and outcome of evolution. Consequently, the study of the genetic basis of adaptive evolutionary change has occupied biologists for decades, but progress has been hampered by the lack of resolution and the absence of a genome-level perspective. Technological advances in recent years should now allow us to answer many long-standing questions about the nature of adaptation. The data gathered so far are beginning to challenge some widespread views of the way in which natural selection operates at the genomic level. Papers in this Special Feature of Proceedings of the Royal Society B illustrate various aspects of the broad field of adaptation genomics. This introductory article sets up a context and, on the basis of a few selected examples, discusses how genomic data can advance our understanding of the process of adaptation.

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Revitalizing Difference in the HapMap: Race and Contemporary Human Genetic Variation Research

The Journal of Law Medicine & Ethics ◽

10.1111/j.1748-720x.2008.293.x ◽

2008 ◽

Vol 36 (3) ◽

pp. 471-477 ◽

Cited By ~ 17

Author(s):

Jennifer A. Hamilton

Keyword(s):

Genetic Variation ◽

Human Genome ◽

Genetic Research ◽

The United States ◽

Genome Project ◽

Human Genetic Variation ◽

Early 21St Century ◽

The Social ◽

English Speaking ◽

The Human Genome Project

In 2000, researchers from the Human Genome Project (HGP) proclaimed that the initial sequencing of the human genome definitively proved, among other things, that there was no genetic basis for race. The genetic fact that most humans were 99.9% the same at the level of their DNA was widely heralded and circulated in the English-speaking press, especially in the United States. This pronouncement seemed proof that long-term antiracist efforts to de-biologize race were legitimized by scientific findings. Yet, despite the seemingly widespread acceptance of the social construction of race, post-HGP genetic science has seen a substantial shift toward the use of race variables in genetic research and, according to a number of prominent scholars, is re-invoking the specter of earlier forms of racial science in some rather discomfiting ways. During the past seven years, the main thrust of human genetic research, especially in the realm of biomedicine, has shifted from a concern with the 99.9% of the shared genome — what is thought to make humans alike — towards an explicit focus on the 0.1% that constitutes human genetic variation. Here I briefly explore some of the potential implications of the conceptualization and practice of early 21st century genetic variation research, especially as it relates to questions of race.

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GENETIC DIVERSITY

PEDIATRICS ◽

10.1542/peds.59.3.432 ◽

1977 ◽

Vol 59 (3) ◽

pp. 432-432

Author(s):

R. C. Lewontin ◽

Keyword(s):

Genetic Diversity ◽

Genetic Variation ◽

Skin Color ◽

Human Genetic Variation ◽

Human Species

Only about 7% of all human genetic diversity is between major races. It would appear then that the superficial characters of skin color, hair form, lip, nose, and eye shape that we use to distinguish human races are atypical and do not represent the mode of human genetic variation. The taxonomic division of the human species into races places a completely disproportionate emphasis on a very small fraction of total human genetic diversity.

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