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Evolution__3rd_Edition

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686 Glossary<br />

isolating mechanism Any mechanism, such as a difference<br />

between species in courtship behavior or breeding season, that<br />

results in reproductive isolation between the species.<br />

isolation Synonym for reproductive isolation.<br />

Lamarckian inheritance A historically misleading synonym<br />

for inheritance of acquired characters.<br />

larva (and larval stage) Prereproductive stage of many<br />

animals; the term is used particularly when the immature stage<br />

has a different form from the adult.<br />

lineage An ancestor–descendant sequence of: (i) populations;<br />

(ii) cells; or (iii) genes.<br />

linkage disequilibrium The condition in which the haplotype<br />

frequencies in a population deviate from the values they would<br />

have if the genes at each locus were combined at random. (When<br />

there is no deviation, the population is said to be in linkage<br />

equilibrium.)<br />

linked Refers to genes present on the same chromosome.<br />

Linnaean classification Hierarchical method of naming classificatory<br />

groups, invented by the eighteenth century Swedish<br />

naturalist Carl von Linné, or Linnaeus. Each individual is assigned<br />

to a species, genus, family, order, class, phylum, and kingdom,<br />

and some intermediate classificatory levels. Species are referred<br />

to by a Linnaean binomial of its genus and species, such as<br />

Magnolia grandiflora. Universally used by educated persons.<br />

locus The location in the DNA occupied by a particular gene.<br />

macroevolution <strong>Evolution</strong> on the grand scale: the term refers<br />

to events above the species level. The origin of a new higher<br />

group, such as the vertebrates, would be an example of a<br />

macroevolutionary event.<br />

macromutation The mutation of a large phenotypic effect;<br />

one that produces a phenotype well outside the range of variation<br />

previously existing in the population.<br />

mean The average of a set of numbers. For example, the mean<br />

of 6, 4, and 8 is (6 + 4 + 8)/3 = 6.<br />

meiosis A special kind of cell division that occurs during the<br />

reproduction of diploid organisms to produce the gametes.<br />

The double set of genes and chromosomes of the normal diploid<br />

cells is reduced during meiosis to a single haploid set. Crossingover<br />

and therefore recombination occur during a phase of<br />

meiosis.<br />

Mendelian inheritance The mode of inheritance of all diploid<br />

species, and therefore of nearly all multicellular organisms.<br />

Inheritance is controlled by genes, which are passed on to the<br />

offspring in the same form as they were inherited from the previous<br />

generation. At each locus, an individual has two genes, one<br />

inherited from its father and the other from its mother. The two<br />

genes are represented in equal proportions in its gametes.<br />

messenger RNA (mRNA) The kind of RNA produced by transcription<br />

from the DNA and which acts as the message that is<br />

decoded to form proteins.<br />

microevolution <strong>Evolution</strong>ary changes on the small scale, such<br />

as changes in gene frequencies within a population.<br />

mimicry A case in which one species looks more or less similar<br />

to another species. See Batesian mimicry, Müllerian mimicry.<br />

mitochondrion A kind of organelle in eukaryotic cells; mitochondria<br />

burn the digested products of food to produce energy.<br />

They contain DNA coding for some mitochondrial proteins.<br />

mitosis Cell division. All cell division in multicellular organisms<br />

is by mitosis except for the special division called meiosis<br />

that generates the gametes.<br />

modern synthesis Synthesis of natural selection and Mendelian<br />

inheritance. Also called neo-Darwinism.<br />

molecular clock The theory that molecules evolve at an<br />

approximately constant rate. The difference between the form<br />

of a molecule in two species is then proportional to the time<br />

since the species diverged from a common ancestor, and<br />

molecules become of great value in the inference of phylogeny.<br />

monophyletic group A set of species containing a common<br />

ancestor and all its descendants.<br />

morphology The study of the form, shape, and structure of<br />

organisms.<br />

Müllerian mimicry A kind of mimicry in which two poisonous<br />

species evolve to look like each other.<br />

mutation When parental DNA is copied to form a new DNA<br />

molecule, it is normally copied exactly. A mutation is any<br />

change in the new DNA molecule from the parental DNA<br />

molecule. Mutations may alter single bases, or nucleotides, short<br />

stretches of bases, or parts of or whole chromosomes. Mutations<br />

can be detected both at the DNA level or the phenotypic level.<br />

natural selection The process by which the forms of organisms<br />

in a population that are best adapted to the environment<br />

increase in frequency relative to less well adapted forms over a<br />

number of generations.<br />

neo-Darwinism (i) Darwin’s theory of natural selection plus<br />

Mendelian inheritance. (ii) The larger body of evolutionary<br />

thought that was inspired by the unification of natural selection<br />

and Mendelism. A synonym of modern synthesis.<br />

neutral drift Near synonym of genetic drift.<br />

neutral mutation Mutation with the same fitness as the other<br />

allele (or alleles) at its locus.<br />

neutral theory (and neutralism) A theory that most evolution<br />

at the molecular level occurs by neutral drift.<br />

niche The ecological role of a species: the set of resources it<br />

consumes, and habitats it occupies.<br />

nucleotide A unit building block of DNA and RNA. A<br />

nucleotide consists of a sugar and phosphate backbone with a<br />

base attached.<br />

nucleus The region of eukaryotic cells containing the DNA.<br />

numerical taxonomy In general, any method of taxonomy<br />

using numerical measurements; in particular, it often refers to<br />

..

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