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Codon Usage Bias

Codon Usage Bias   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...Usage Bias Living organisms use 20 amino acids to construct their protein molecules. These amino acids are coded for by 64 codons of three nucleotides (e.g., the sequence TTT codes for phenylalanine). Almost all organisms use the same genetic code, which is referred to as the “universal code” (Table 1). Of the 20 amino acids, 18 are encoded by more than one codon. However, these synonymous codons (different codons that code for same amino acid) are not used uniformly; in almost every organism that has been studied, there are distinct preferences for...

Comparative Method

Comparative Method   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
4,461 words
Illustration(s):
4

...states {G1,G2} on two traits: G1 refers to the character state of trait 1, and G2 to the character state of trait 2. Four other species, all descendant from a different common ancestor, take the values {g1,g2}. Let G1 signify the presence of some trait and g1 its absence; likewise for G2 and g2. The relationship counted across the eight species is perfect: G1 always pairs with G2 and g1 always pairs with g2. But the phylogeny reveals that the pairing {G1,G2} probably evolved only once from {g1,g2}. By comparision, the relationship {G1,G2} evolves...

Plagues and Epidemics

Plagues and Epidemics   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...(2000): 1789–1796. Evidence that the virus causing AIDS entered the human population sometime around 1930. Pier, G. B. , M. Grout , T. Zaidi , G. Meluleni , S. S. Mueschenborn , G. Banting , R. Ratcliff , M. J. Evans , and W. H. Colledge . “ Salmonella typhi Uses CFTR to Enter Intestinal Epithelial Cells. ” Nature 393 (1998): 79–82. Analysis of a mutation that protects against typhoid fever. Raoult, D. , G. Aboudharam , E. Crubezy , G. Larrouy , B. Ludes , and M. Drancourt . “ Molecular Identification by ‘Suicide PCR’ of Yersinia pestis as the...

Lichens

Lichens   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...(e.g., Trentepohlia and Myrmecia ) are facultative photobionts, known to occur independently as epiphytes, endoliths, or soil algae. They often have growth rates in culture that are similar to those of axenic cultures of free-living algal species that are never found in lichens. However, the free-living ability of some of the other most commonly found photobionts in lichens is still unclear (e.g., Trebouxia ). Symbionts grown separately do not exhibit the complex growth forms (e.g., crustose, foliose, and fruticose thalli) and structures (e.g.,...

Maternal-Fetal Conflict

Maternal-Fetal Conflict   Reference library

Encyclopedia of Evolution

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Subject Reference
Current Version:
2005

... Development Genes and Evolution 210 (2000): 18–20. Robillard, P.-Y. , G. A. Deckker , and T. C. Hulsey . “ Revisiting the Epidemiological Standard of Preeclampsia: Primigravidity or Primipaternity. ” European Journal of Obstetrics, Gynecology, and Reproductive Biology 84 (1999): 37–41. Shine, R. “The Evolution of Viviparity in Reptiles: An Ecological Analysis.” In Biology of the Reptilia , edited by C. Gans and F. Billet , vol. 15, pp. 605–694. New York, 1985. Spencer, H. G. , M. W. Feldman , and A. G. Clark . “ Genetic Conflicts, Multiple Paternity...

Convergent and Parallel Evolution

Convergent and Parallel Evolution   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
1,982 words
Illustration(s):
3

...to mere similarity owing to chance. At the molecular level, this distinction becomes very important because of the limited number of possible character states for nucleotides (one for each of the four nucleotides making up strands of DNA) and for amino acids (20 possible character states representing the 20 amino acids). The existence of convergent evolution in morphological, physiological, behavioral, and molecular changes indicates that there are significant constraints on the evolutionary process, and that these constraints are distributed across the...

Experimental Evolution

Experimental Evolution   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
3,999 words
Illustration(s):
1

...is the familiar form used in animal and plant breeding, and it can sometimes quickly result in the creation of new types of organisms (e.g., breeds of dogs). However, by imposing a single desirable factor or set of factors, it may constrain the pathways along which evolution can proceed to solve a more general problem. The third approach is laboratory culling. In this design, a more extreme environmental condition (e.g., high temperature) is imposed every generation, and only a small proportion of the population is permitted to survive to reproduce the next...

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

...carbon from plants. Ants Ants associated with various plants (e.g., Acacia, Cecropia ). Ants protect plants from herbivores. Ants obtain nest site and food (e.g., secretions of extrafloral nectaries, proteinaceous bodies) from plants. Ants nesting in epiphytes (e.g., Myrmecodium ) Ants obtain protected nest site in hollow plant organ. Plants obtain nutrients absorbed from ant nest site. B. Animal Hosts Photosynthetic algae Dinoflagellate Symbiodinium in marine animals (e.g., corals). Chlorella in freshwater animals. Animals derive photosynthetic...

Cancer

Cancer   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

..., D. Gardiol , F. Mantovani , J. Breuer , I. M. Leigh , G. Matlashewski , and L. Banks . “ Role of a p53 Polymorphism in the Development of Human Papillomavirus-associated Cancer. ” Nature 393.6682 (1998): 229–234. Struewing, J. P. , P. Hartge , S. Wacholder , S. M. Baker , M. Berlin , M. McAdams , M. M. Timmerman , L. C. Brody , and M. A. Tucker . “ The Risk of Cancer Associated with Specific Mutations of BRCA1 and BRCA2 among Ashkenazi Jews. ” New England Journal of Medicine 336.20 (1997): 1401–1408. Weber, B. L. “ Update on Breast Cancer...

Self-deception

Self-deception   Reference library

Encyclopedia of Evolution

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Subject Reference
Current Version:
2005

...not well understood, we do know enough to question the common impression that information reaching our brain is immediately registered in consciousness, and that signals to initiate activity always originate in the conscious mind. While a nervous signal reaches the brain in only 20 milliseconds, it takes a full 500 milliseconds for the signal to register in consciousness. This is all the time in the world, so to speak, for emendations, changes, deletions, and enhancements to occur. Indeed, neurophysiologists have shown that stimuli can affect the content of...

Species Concepts

Species Concepts   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...are made to apply the many species concepts available. Richard G. Harrison See also Speciation . Baum, D. A. , and M. J. Donoghue . “ Choosing among Alternative ‘Phylogenetic’ Species Concepts. ” Systematic Botany 20 (1995): 560–573. One view of the disagreements among cladists as to how to define species. Baum, D. A. , and K. L. Shaw . “ Genealogical Perspectives on the Species Problem. ” In Experimental and Molecular Approaches to Plant Biosystematics , edited by P. C. Hoch and A. G. Stevenson , pp. 289–303 St. Louis, 1995. A provocative...

Arthropods

Arthropods   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...See also Animals ; Insects . Edgecombe, G. D. Arthropod Fossils and Phylogeny . New York, 1998. Fortey, R. A. , and R. H. Thomas . Arthropod Relationships . London, 1998. Giribet, G. , D. L. Distel , M. Polz , W. Sterrer , and W. C. Wheeler . “ Triploblastic Relationships with Emphasis on the Acoelomates, and the Position of Gnathostomulida, Cycliophora, Platyhelminthes, and Chaetognatha: A Combined Approach of 18S rDNA and Morphology. ” Systematic Biology 49 (2000): 539–562. Giribet, G. , G. D. Edgecombe , and W. C. Wheeler . “ Arthropod...

Sex, Evolution of

Sex, Evolution of   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
6,244 words
Illustration(s):
5

...Early theoretical work suggested that the deleterious mutation rate needed to be greater than 1.0 per genome per generation to balance the twofold cost of sex, but more realistic models suggest that several other factors (e.g., finite populations, variation in the extent of epistasis) mean that a mutation rate greater then approximately 2.0 is required. Figure 3. Interactions Between Deleterious Mutations.The relationship between (log) fitness and the number of deleterious mutations may be linear (multiplicative); each extra mutation lead to a greater decrease...

DNA and RNA

DNA and RNA   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...)—or a purine, guanine ( G ) or adenine ( A ). The pentose sugar component can be either ribose or deoxyribose. Nucleotides can link together in a chain through the formation of phosphodiester bonds between the 5′ phosphate group on the sugar residue of one nucleotide and the 3′ hydroxyl group of the next. DNA and RNA are distinguished by the kind of 5-carbon sugar- and nitrogen-containing bases carried by their nucleotide subunits. The nucleotide subunits in DNA have deoxyribose as their pentose sugar component and either A, T, G, or C as a base. RNA...

Mammals

Mammals   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
5,871 words
Illustration(s):
1

...Cambridge, 1993. Gatesy, J. , and P. Arctander . “Molecular Evidence for the Phylogenetic Affinities of the Ruminantia.” In Antelopes, Deer and Relatives , edited by E. S. Vrba and G. B. Schaller , pp. 143–155. New Haven, 2000. Gatesy, J. , et al. “ Stability of Cladistic Relationships between Cetacea and Higher Level Artiodactyl Taxa. ” Systematic Biology 48 (1999): 6–20. Gingerich, P. D. , et al. “ Origin of Whales in Epicontinental Remnant Seas. ” Science 220 (1983): 403–406. Griffiths, M. The Biology of the Monotremes . New York, 1978. Hotton, N....

Cytoplasmic Genes

Cytoplasmic Genes   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...through the egg. In plants and protists (unicellular eukaryotes), there is a greater diversity of inheritance modes. Maternal inheritance of organelle DNA is most common in plants, but paternal inheritance is also known (e.g., both chloroplasts and mitochondria in Sequoia sempervirens , the redwood tree), as is biparental inheritance (e.g., chloroplasts in Pelargonium , the geranium). It is notable that in some species, like the unicellular alga Chlamydomonas , mitochondria and chloroplasts are inherited uniparentally, but each from a different parent. The...

Homology

Homology   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...a Head. ” BioEssays 23 (2001): 8–11. Shubin, N. , and P. Alberch . “ A Morphogenetic Approach to the Origin and Basic Organization of the Tetrapod Limb. ” Evolutionary Biology 20 (1986): 319–387. Van Valen, L. “ Homology and Causes. ” Journal of Morphology 173 (1982): 305–312. Wagner, G. P. “ The Biological Homology Concept. ” Annual Review of Ecology and Systematics 20 (1989): 51–69. Günter P....

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

...so that both parties know what taxon is being referred to, names ideally should be stable over time, universal in their application, and unambiguous in their meaning. Common names typically fail to meet these criteria. Many species have more than one common name (e.g., the cougar has more than 20 other common names, including mountain lion and puma), and different species are sometimes referred to by the same name (“lily” is used for various other plants). Formal biological nomenclature attempts to avoid the communication problems associated with multiple,...

Malaria

Malaria   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
2,563 words
Illustration(s):
2

...on these observations, the current distribution of P. falciparum throughout the world's tropical regions is believed to have derived from a small ancestral population within the past 20,000 to 60,000 years. Evidence exists to show that natural selection acts strongly on both the falciparum and its hosts. The human response is evident in the various hemoglobinopathies (e.g., sickle-cell trait) that have arisen to combat the Plasmodium . The P. falciparum genotype itself shows evidence of positive selection among several genes encoding immunogenic surface...

Molluscs

Molluscs   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
5,973 words
Illustration(s):
1

...predominantly marine and tropical (e.g., Nerita ) but has successfully invaded brackish water and rivers (e.g., Neritina ). The largest gastropod clade is the Caenogastropoda, comprising most of the former Mesogastropoda plus the Neogastropoda. This group is predominantly marine but includes some freshwater and terrestrial taxa. The univalve shells are helically coiled, and most caenogastropods have a radula with rather few (2–7) teeth in each row. Caenogastropodan feeding types are extremely diverse, including grazing (e.g., Littorina ), suspension and...

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