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Protein Folding

Protein Folding   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...interactions, the cell utilizes a set of special proteins known as chaperones that protect the nascent chains from forming nonnative complexes. Structure Although the total possible number of different amino acid sequences composed of the 20 protogenic amino acids is immense (for a chain of 150 amino acids long the number is 20 150 or approximately 10 195 ), and the number of possible three-dimensional conformations they can theoretically adopt is even greater, the total number of stable three-dimensional structures allowed by physics would appear to be...

Sibling Rivalry

Sibling Rivalry   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...other birds, fatalities are conditional on various outside forces, mainly associated with food deliveries. Nestling aggressiveness may itself be adjusted according to food amounts, as shown experimentally for blue-footed boobies ( Drummond and Osorno , 198x ) and ospreys ( Machmer and Ydenberg 199x ), or it may remain relatively steady, as in egrets, with the subordinate chick's ability to withstand physical abuse conditional on the amount of food it receives ( Mock et al., 1987 ). Examples of Siblicide Although avian siblicide has been known for at...

Symbiosis

Symbiosis   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
3,425 words
Illustration(s):
2

...Figure 1. The Light Organ in Leiognathid Fish Leiognathus equulus .(A) Diagrammatic vertical section showing the relationship ofthe light organ (lo) and gas bladder (gb), and the path oflight (dashed lines and arrows) emitted from the light organ. (B) Cross section of (A) at X-X' showing relative position oflight organ and gas bladder. McFall-Ngai (1983) AmericanZoologist. © 1983. Reprinted by permission of Wiley-Liss, Inc., asubsidiary of John Wiley & Sons, Inc. Many ant-tended plants display morphological innovations that attract ants to the plant and...

Molecular Evolution

Molecular Evolution   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
4,573 words
Illustration(s):
5

...as possible ( Li , 1997 ). As an illustration, we consider maximizing the number of matched pairs between two sequences. Let w k be the penalty for a gap of k nucleotides. Then the Needleman-Wunsch similarity measure between two aligned sequences is defined as S = x − ∑ w k Z k where x = number of matches, z k = the number of gaps of length k , and w k = the penalty for gaps of length k . The most commonly used penalty function is w k = a + bk , where a and b are nonnegative parameters. However, even with this system, how to choose a ...

Hybrid Zones

Hybrid Zones   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
3,039 words
Illustration(s):
2

...passes and hills below 2100 meters. The zone is fairly narrow but varies in width from place to place. The cline width, in which a character changes gradually from pure parallelus to pure erythropus , varies among characters (e.g., that for an X-chromosome C-band is <2km, while that for song syllable length is >20km). Most characters have broadly coincident clines, but a few are displaced from the center (Figure 2). These details vary among transects in different places across the Pyrenees, which reflects the complex interaction of many genes hybridizing...

Nomenclature

Nomenclature   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
3,807 words
Illustration(s):
2

...clade consisting of all organisms more closely related to B than to A” or “the most inclusive clade that includes B but not A.” A possible definition of the apomorphy-based clade is “the clade stemming from the first organism to possess character X synapomorphic with that in B.” The bar marks the origin of character X. The species names and characters referred to in phylogenetic definitions are called specifiers.Courtesy of Harold N. Bryant. Figure 2. The Effect of Changes in Phylogenetic Relationships on the Use of Phylogenetic Definitions.Given a taxon name...

Cambrian Explosion

Cambrian Explosion   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...molecular biology and the use of so-called molecular “clocks.” In principle, the more distantly related the organism, the greater the difference in molecular sequence, say, the composition of the strings of amino acids that make up a protein. If the substitutions (e.g., at site X a glycine replaces a valine) occur at a more or less constant rate—for example, one on average every million years—then in principle the time of original divergence of the two living species can be estimated. Everyone knows that there are a variety of molecular “clocks,” some...

DNA and RNA

DNA and RNA   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...information is carried. The challenge to biologists was to work out the structure of the DNA molecule, and to explain how the sequence of bases encoded information. Francis Crick and James Watson were the first to describe the structure of DNA. Their model was partly based on X-ray diffraction photographs, taken by Maurice Wilkins and Rosalind Franklin , that showed great consistency and symmetry in the structure of DNA and gave important clues about its dimensions. Also key to Watson and Crick's model was Edwin Chargaff's 1949 observation that, in...

Disease

Disease   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
9,315 words
Illustration(s):
1

...and they exhibit local geographic distributions ( Weatherall , 2001 ). Glucose-6-phosphate dehydrogenase deficiency. Along with sickle cell and thalassemia, another genetic disorder that is elevated in frequency in regions where malaria is common is G6PD deficiency. This X-linked gene encodes the lead enzyme in the pentose phosphate shunt, which generates NADPH for many cellular oxidation-reduction or redox reactions. The precise mechanism whereby this change results in elevated resistance to malaria is not known. Complete loss of G6PD activity is...

Human Genetic and Linguistic Diversity

Human Genetic and Linguistic Diversity   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
8,001 words
Illustration(s):
5

...last 100,000 years is mostly based on the NRY genealogy, but in principle it is in good agreement with mtDNA data and with earlier conclusions obtained by tree and PC analysis of populations using protein data, as well as with the less abundant data on DNA of other autosomal and X chromosome genes. Yet protein data have inevitably less power, and the study of DNA of one autosomal gene, analyzed separately from the rest, can provide more limited information. Some genes show a complex history, strongly affected by specific natural selection. An autosomal...

Hominid Evolution

Hominid Evolution   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
14,569 words
Illustration(s):
5

...New Age Estimates for the Swanscombe Hominid, and Their Significance for Human Evolution. ” Journal of Human Evolution 37 (1999): 873–877. A recent article reevaluating the tempo and mode of human evolution during the European Middle Pleistocene. Zhu, R. X. , K. A. Hoffman , R. Potts , C. L. Deng , Y. X. Pan , B. Guo , C. D. Shi , Z. T. Guo , B. Y. Yuan , Y. M. Hou , and W. W. Huang . “ Earliest Presence of Humans in Northeast Asia. ” Nature 413 (2001): 413–417. Juan Luis Arsuaga Neanderthals Neanderthals (or Neandertals; see ) are a group of...

Life History Theory

Life History Theory   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
11,243 words
Illustration(s):
4

...affect the life histories of their carriers in specified ways spread in the population (see Figure 1). The two main ways to consider fitness are outlined below. For simplicity, this is done only for females. Figure 1. The Main Types of Animal Life-History Models.In each case the x-axis is age. In (A) females breed for the first time at age tj years, when they produce n daughters, then die. This type of life history, in which animals breed once then die, is referred to as semelparity. Alternatively animals may breed repeatedly, as in (B) and (C), this is...

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