Glossary of Key Terms

Chapter 3: Biology and Evolution

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Adaptation
A process by which organisms achieve a beneficial adjustment to an available environment; also the results of that process-the characteristics of organisms that fit them to the particular set of conditions of the environment in which they are generally found.

Alleles
Alternate forms of a single gene.

Analogies
In biology, structures that are superficially similar; the result of convergent evolution.

Anthropomorphism
The ascription of human attributes to nonhuman beings.

B

Branching evolution
An evolutionary process in which an ancestral population gives rise to two or more descendant populations that differ from one another.

C

Catastrophism
The view that layers of fossils were evidence of new acts of devine creation.

Chromosome
In the cell nucleus, long strands of DNA combined with a protein that can be seen under the microscope.

Codon
Three-base sequence of a gene that specifies production of an amino acid.

Convergence
A process by which unrelated populations develop similarities to one another.

D

DNA
The genetic material deoxyribonucleic acid; a complex molecule with information to direct the synthesis of proteins. DNA molecules have the unique property of being able to produce exact copies of themselves.

Directional selection
Natural selection that favors a single allele and therefore allele frequency continuously shifts in one direction.

Disruptive selection
Natural selection that simultaneously favors individuals at both extremes of the distribution.

Divergent evolution
An evolutionary process in which an ancestral population gives rise to two or more descendant populations that differ from one another.

E

Enzyme
Proteins that initiate and direct chemical reactions in an organism.

Evolution
Descent with modification.

G

Gene flow
The introduction of alleles from the gene pool of one population into that of another.

Gene pool
The genetic variants available to a population.

Genera
In the system of plant and animal classification, a group of like species.

Genes
Portions of DNA molecules that direct the synthesis of proteins. DNA molecules have the unique property of being able to produce exact copies of themselves.

Genetic code
The sequence of DNA bases that specifies production of a particular amino acid.

Genetic drift
Chance fluctuations of allele frequencies in the gene pool of a population.

Genome
The complete sequence of DNA for a species.

Genotype
The actual genetic makeup of an organism.

Genus
In the system of plant and animal classification, a group of like species.

H

Hardy-Weinberg principle
Demonstrates algebraically that the percentage of individuals that are homozygous for the dominant allele, homozygous for the recessive allele, and heterozygous should remain constant from one generation to the next, provided that certain specified conditions are met.

Hemoglobin
The protein that carries oxygen in the red blood cells.

Heterozygous
Refers to a chromosome pair that bears different alleles for a single gene.

Homeobox genes
Regulatory genes that code for proteins that travel to other homeobox genes and activate or deactivate them at different times.

Homologis
In biology, structures possessed by two different organisms that arise in similar fashion and pass through similar stages during embryonic development.

Homozygous
Refers to a chromosome pair that bears identical alleles for a single gene.

I

Interspecies gene transfer
Transfer of DNA as when retroviruses insert DNA into the cells of one species from another.

Isolating mechanisms
Factors that separate breeding populations, thereby preventing gene flow, creating divergent subspecies and ultimately (if maintained) divergent species.

L

Law of dominance and recessiveness
Certain alleles are able to mask the presence of others.

Law of independent assortment
Genes controlling different traits are inherited independently of one another.

Law of segregation
Variants of genes for a particular trait retain their separate identities through the generations.

M

Meiosis
A kind of cell division that produces the sex cells, each of which has half the number of chromosomes, and hence genes, as the parent cell.

Mitosis
A kind of cell division that produces new cells having exactly the same number of chromosome pairs, and hence genes, as the parent cell.

Mutation
Chance alteration of a gene that produces a new allele.

N

Natural selection
The evolutionary process through which factors in the environment exert pressure that favours some individuals over others to produce the next generation.

Notochord
A rodlike structure of cartilage that, in vertebrates, is replaced by the vertebral column.

P

Phenotype
The physical appearance of an organism that may or may not reflect a particular genotype because the latter may or may not include recessive alleles.

Polygenetic inheritance
When two or more genes work together to effect a single phenotypic character.

Population
In biology, a group of similar individuals that can and do interbreed.

Primates
The group of mammals that includes lemurs, lorises, tarsiers, monkeys, apes and humans.

Punctuated evolution
A new species appears after a relatively quick and dramatic change then lasts for a long time with little significant change.

R

RNA
Ribonucleic acid; similar to DNA but with uracil substituted for the base thymine. Carries instructions from DNA to produce amino acids for protein building.

Race
In biology, a population of a species that differs in the frequency of the variants of some gene or genes from other populations of the same species.

Regulatory genes
Control the expression or activity of other genes.

Ribosomes
Structures in the cell where translation occurs.

S

Sickle-cell anemia
An inherited form of anemia caused by the red blood cells assuming a sickle shape.

Species
In biology, a population or group of populations that is capable of interbreeding but that is reproductively isolated from other such populations.

Stabilizing selection
Natural selection as it acts to promote stability, rather than change, in a population's gene pool.

Structural genes
Code for proteins that contribute directly to the actual formation of a structure such as whether a person has brown or blue eyes.

T

Transcription
Process of conversion of instructions from DNA into RNA.

Translation
Process of conversion of RNA instructions into proteins.

U

Unifomitarianism
The view that forces shaping the contemporary world were no different in the past.