Synthetic theory of evolution: A theory
combining the following 3
points - 1) the environment determines which individual
characteristics produce the largest number of successful offspring
(=natural selection); 2) genes determine the traits on which
natural
selection acts and mutations arising at random produce variations
in
genes; 3) reproductive isolation of parts of a population allows
these parts to adapt to their environments independently of one
another.
Reproductive isolation: When individuals
cannot produce offspring,
they are reproductively isolated from one another. They may be
isolated only because they occur in different places and never
meet.
They may be isolated because they are so different that, even if
they mated, no offspring would result - they would be different
species.
DNA: Deoxyribonucleic acid are molecules
that carry genetic
information, that is, the genes. The molecules are composed of
various combinations of 4 nucleotide bases that, in groups of 3
(=triplets), form the genetic code of the genes that specifies the
20 various amino acids that make up proteins.
Molecular determinism: The idea that the
chemical structure of the
DNA molecule is more likely to change in certain places than in
others - so that mutations really do not occur at random within the
gene.
Neutral theory: The concept that chance
determines the initial
appearance of mutations, and that most of these mutations have no
effect (i.e., the mutation is neutral) on the fitness of the
organisms.
Punctuated equilibrium: The theory that
evolution produces groups of
species that are stable for long periods of time, but development
of
new species occurs rapidly when there is a significant change in
the
environment.
Polyploidy: The possession of more than
2 sets of chromosomes. If a
gamete contains 1N chromosomes, then the zygote contains 2N
chromosomes. A polyploid would contain 3N, 4N, etc., chromosomes.
Tandem multiplication: The repetition of
a sequence of nucleotide
bases in adjacent sites along a chromosome.
Nucleotide base: A molecule, of 4 types,
that are the building
blocks of DNA - adenine, cytosine, guanine, and thymine. These 4
nucleotides can form 64 different combinations in groups of 3.
Amino acid: Molecules that are the basic
building blocks of
proteins. There are 20 that are found in proteins.
Polypeptide: A chain of amino acids. A
protein may consist of one or
more polypeptides.
Collagen: The main structural protein of
bone, cartilage, connective
tissue, and skin in vertebrates.
Exon: A sequence of DNA that is a part of
a gene. Exons may be
separated by introns.
Intron: A sequence of DNA that is not
part of a gene and is
interspersed between exons.
Immumoglobulin: A protein important in
the immune system, that
consists of 2 large ("heavy") chains and 2 smaller ("light")
chains.
Point mutation: A change in one of the
nucleotide bases in DNA,
i.e., a mutation at one point in the DNA molecule.
Pseudogene: A sequence of DNA, similar to
the sequence for an active
gene, but that does not produce a protein. It could be a duplicated
copy of a gene that contains a mutation that inactivates the
copy.
Plasmid: A small, circular bit of DNA
that can carry genetic
material from one cell to another.
Coadaptation: The products of different
genes work together and
complement one another. In addition to the importance of the
protein
that the gene codes for, the ability of that protein to work
together with other proteins is also important.
Electrophoresis: A technique in which
proteins of differing electric
charge and mass are separated from one another when subjected to an
electric current for a period of time.
Natural selection: The process by which
individuals that are better
adapted to an environment survive, reproduce, and leave more
descendants than other individuals (which are not as well adapted
to
that environment). Thus, the environment "selects" those
individuals
which leave more descendants.
Degree of heterozygosity: The proportion
of gene locations that
contain different alleles. That is, the allele for a gene on the
chromosome from the male parent is different from the allele on the
chromosome from the female parent. The proportion of heterozygous
genes has been found to range from 5-20% in an individual.
Codon: A triplet of nucleotide bases that
codes for an amino acid.
Silent mutation: A change in one of the
nucleotide bases of a codon
that specifies the same amino acid that the unchanged codon
specified. Some amino acids are specified by more than one codon -
there is redundancy in the genetic code.
Fossil record: The fossil specimens that
have been dug out of rocks
and soil, that are the remains of organisms that have gone
extinct.
Histone: A nuclear protein that combines
with DNA to form the
chromosome. Certain histones are identical in all organisms that
have been studied, implying that changes (i.e., mutations) in the
structure of these proteins has always decreased fitness.
Gradualism: The idea that evolution
proceeds in small steps.
Gradualism implies that there should be found fossils of organisms
that are intermediate between others.
Mosaic evolution: The fact that different
parts of an organism
change at different rates in evolution. For example, arms and legs
may change faster than the head or the trunk of the body.
Morphology: The study of the different
forms that organisms have.
For example, the study of the differences in form between dogs and
cats.
Morphological differentiation: The
development of differences in the
form of organisms, e.g., between horses and zebras.
Species selection: The survival of one
species rather than another,
as opposed to the survival of one individual rather than another.
The idea is that a species with a certain attribute, e.g., the
ability to run fast, will have a higher fitness than another. In
an environment where running fast is important, the first species
will displace the second. This contrasts with the notion that
faster
individuals in both species will survive. The emphasis here is
selection on the group of individuals rather than on individuals
within the group.
Nucleotide pair: A pair of nucleotide
bases, which takes up one
position of the DNA molecule. Since the DNA occurs on the
chromosome
as a double strand, one member of the nucleotide pair occurs on one
strand and the other member occurs on the other strand. Moreover,
since adenine always pairs up with thymine and cytosine with
guanine, the pairs are A-T and C-G.
Complexity of organisms: Organisms are considered to be more complex, the more recently they have appeared in the fossil record. That is, viruses are relatively simple, bacteria more complex, and eukaryotes most complex. There is a general trend for more complex organisms to have a larger amount of genetic material (i.e., the number of nucleotide bases).
Organism Number of Nucleotide Pairs/Cell -------- ------------------------------- Virus 1,300-20,000 Bacteria 4,000,000 Fungi 10,000,000-20,000,000 Plants and Animals 3,000,000,000
DNA repetitions: The presence on a
chromosome of a sequence of
nucleotide pairs in multiple copies with no apparent function. For
example, the Alu sequence in humans is 300 nucleotide pairs in
length and is present in about 300,000 copies. These repetitions
seem to be meaningless with respect to the function of the
person.
Circularity: A kind of reasoning starting
with an assumption and
ending with a conclusion, which is used to justify the assumption.
For example, it is said that species which occupy the same
ecological niche cannot coexist in the same habitat. When two
species are found to coexist, it is concluded that they do not
occupy the same niche. A properly justified conclusion would be
based on a study of species habits that shows that their niche
parameters are really different.
Discontinuity: A break in an otherwise
continuous pattern. For
instance, if species change gradually to remain well adapted to a
gradually changing environment, a discontinuity in this pattern
would be the rapid evolution of new species in response to the
opening up of new habitats - such as an adaptive radiation by
colonists which first reach an island.
Microsphere: A microscopic, carbonized
sphere composed of organic
matter. Microspheres are considered to be the first fossil evidence
of life. They have been found in ancient rocks from sediments dated
to be 3.4 billion years old.
Oparin-Haldane hypothesis: In the 1920's
the Russian Alexander
Oparin and the British John B. S. Haldane suggested a scenario for
the origin of life on earth.
1) A nonoxidizing atmosphere was present.
2) Liquid water was present.
3) Small inorganic molecules were available.
4) There were energy sources for the synthesis of organic
molecules.
a) Solar radiation
b) Electricity from lightning discharges
c) Volcanic heat
d) Radioactive decay produced heat
5) Organic molecules accumulated in aqueous solution from slow,
spontaneous reactions without enzymes and in the absence of
consumers.
Abiotic synthesis: The production of
organic compounds in a
nonliving system. In 1953 Stanley Miller simulated the
Oparin-Haldane hypothesis in the laboratory with
1) Raw materials - methane (CH3), ammonia (NH3), oxygen (H2O), and
hydrogen (H2)
2) Spark discharge as an energy source
3) Boiled the water in one part and condensed the steam in another
so that ambient temperature ranged from 0-100 C
4) Initially sterilized the apparatus
5) Control apparatus without the electric discharge
6) Found a regular production of amino acids from simple
condensation reactions
Murchison meteorite: Fell in 1969 on
Murchison, Australia. The
carbon-containing meteorite also contained some of the familiar
amino acids of Earth, as well as some unlike Earth's.
Polymerization: The production of chains
of molecular compounds,
composed of monomer units. Polymerization requires an energy source
and the absence of water if the reactions are spontaneous.
Monomer: The basic subunit of a larger
functional molecule, e.g.,
amino acids, sugars, nucleotides are the basic subunits of
polypeptides, starches, and polynucleotides (like RNA and DNA),
respectively.
Spontaneous reaction: A reaction that
proceeds on its own. Most
organic reactions require a significant activation energy, with the
result that rate of the spontaneous reaction is extremely slow.
Activation energy: The energy required to
initiate a chemical
reaction, i.e., to break the bonds of the molecules that will
react.
Catalyst: A substance that facilitates a
chemical reaction. That is,
the catalyst "bends" the reactant molecules so that their bonds
break more easily. The catalyst itself is unchanged in the process.
Various metals, such as iron, zinc, and magnesium act as
catalysts.
Enzyme: Organic catalyst, protein, for
the most part. Enzymes are
highly specific to their reactions, and efficiently facilitate
these
reactions within the cellular environment under mild temperature
and
low pressure.
Exergonic: Releasing energy, as in a
chemical reaction. In living
systems, the energy released can be coupled to reactions that
require energy.
Endergonic: Requiring energy, as in a
chemical reaction. In living
systems, the energy required is usually obtained from reactions
that
release energy.
Coacervate: A droplet of water in which
electrically charged
particles are suspended. Simple coacervates possess a boundary
layer
of water molecules, which separates the molecules held inside the
droplet from the external aqueous medium.
Proteinoid: Protein-like molecules formed
by heating dry amino acids
to about 130 C. Cooling the proteinoids in water produces
microspheres similar in size and shape to coccid bacteria. The
microspheres have an semipermeable boundary layer and they can be
caused to simulate budding.
Liposome: Phospholipid vesicle. A
phospholipid is a molecule with a
polar phosphoric acid group on one end and a nonpolar fatty acid
group on the other. In water the phospholipids aggregate
spontaneously into
1) Micelles with the hydrophilic, polar heads outward and the fatty
acid tails inward, or
2) Bimolecular layer with the heads out and the tails in, similar
to
cell membranes.
The liposomes act like semipermeable membranes and absorb organic
molecules from the aqueous medium.
Protobiont: The prelife entity that
ultimately evolved into a true
life form, or eubiont, and has been suggested to be a structure
resembling a coacervate, liposome, or proteinoid microsphere.
Molecular fossil: A chemical structure or
function in today's
organisms, that probably was present in ancient life forms - that
is, in ancestors of modern species. For example, there are many
organsims that have parts of their DNA organized in the same way,
and there are many organisms that use the same metabolic pathways.
Because all these organisms share these molecular characteristics
in
common, we conclude that they were present in a common ancestor of
today's species.
Compartmentation: The separation of the
organic molecules ("the
living system") from its environment. The compartment was possibly
bounded by a membrane composed of lipid. As a result, organic
molecules were protected from destructive external forces, and
could
remain inside in relatively high concentrations.
Conserved function: Some of the
physiological reactions in organisms
will work only in a certain way, e.g., the cytochrome system of
cellular respiration, histones. Organisms with mutations in these
reactions are unsuccessful in leaving offspring. Therefore, these
reactions are remarkably similar in all living organisms, being
conserved throughout the course of evolution. The sharing of
conserved function among many organisms is strong evidence showing
that modern species evolved from a common ancestor.
Prokaryote: The 2 groups are eubacteria
and archebacteria.
Considered to be the first cellular form of life on Earth,
prokaryotes contain no intracellular compartments. The DNA is
circular, is attached to the cell membrane, and the cell has an
external cell wall.
Eukaryote: Organisms whose cells contain
internal compartments,
e.g., a nucleus in which the DNA is located, and an internal
cytoskeleton. These structural features allow eukaryote cells to
communicate with other cells and to aggregate into multicellular
groups.
Giardia: A genus of intestinal parasites,
considered by some to be a
missing link between prokaryotes and eukaryotes. They share some
characteristics with prokaryotes and some with eukaryotes.
Serial endosymbiosis: The successive
incorporation of smaller cells
into a larger host to the mutual benefit of both organisms. For
instance, an aerobic prokaryote could have been engulfed by an
anaerobic prokaryote, allowing the latter to use oxygen for respi-
ration and providing the former with nutrients. The mitochondrion
could have originated by this process. Other possible associations
include chloroplasts and flagella.
Ribosome: A form of ribonucleic acid,
used as a "platform" on which
protein synthesis occurs, guided by messenger RNA.
Cyanobacteria: Sometimes called
blue-green algae, these prokaryotes
are photosynthetic and use chlorophyll to capture sunlight.
Teleology: The explanation of natural
phenomena as evidence of
design or purpose. In other words, the idea that organisms evolve
the way they do in order to reach a particular goal.
Microfossils: Organic material of ancient
age - about 3.5 billion
years old - thought to be evidence of the earliest living creatures
on the earth.
Protein: A nitrogen-containing organic
molecule made up of amino
acids. Structural proteins, like collagen, are the building blocks
of the body. Catalytic proteins, like enzymes, control the rate of
cellular reactions. Regulatory proteins interact with genes to
control their expression.
RNA: Molecules of ribonucleic acid relay
the genetic messages in the
DNA to action in the cell. The genetic message in DNA is
transcribed
to an identical message in RNA, which is subsequently translated
into proteins. It is hypothesized that early life was based on RNA.
Clade: A cluster of taxa derived from
a single common ancestor.
Cladistics: Classification based on
grouping taxa by their shared possession of similar ("derived")
characters that differ from the ancestral condition.
Taxon: A unit of classification
containing a distinctive group of organisms. The unit may be a
species, a genus, a family, an order, etc. The plural of taxon is
taxa.
Last updated on January 30, 2004
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