Biology Lessons Part 2: Population Biology

Lesson 2.4: Glossary: How Do Organisms Vary?

allele - one of the alternative forms of a gene having a distinct genotype and often, a distinct phenotype.

community - a group of organisms made up of two or more different species living together within the same geographical area where they are likely to interact with each other; example, a forest community.

continuous variation - phenotype variation shown in quantitative traits which are distributed from one extreme to another in an overlapping, continuous spectrum; examples of traits that show continuous variation are height, weight, and intelligence.

dominant - the trait which has a detectable phenotype in a heterozygous gene pair; a dominant allele is symbolized using a capital letter (e.g. B).

environmental influences - the complex of geographic, climatic, and social forces which may effect or repress the expression of genes.

expressed - the translation of a gene into a detectable trait in an organism.

gene - the fundamental unit of heredity. Normal (diploid) organisms have two copies of each gene (which are alleles) in their genome.

genotype - the genetic constitution of an organism or of a single pair of alleles (e.g. Bb) of that organism.

Gregor Mendel - a Slovakian monk who studied genetic patterns in cross-fertilized pea plants. Gregor Mendel was the first to propose a particulate hypothesis of heredity, predicting the gene as the fundamental unit of heredity.

heterozygous - the state of having two different alleles of a particular gene (e.g. Aa).

homozygous - the state of having two identical alleles of a particular gene (e.g. AA, aa).

Mendelian traits - characteristics which follow the simple patterns of inheritance proposed by Gregor Mendel; a trait produced by a single gene.

metric system - a system of quantitative measurement based on the decimal system (10). The metric system can be used to quantify length, mass, and volume.

phenotype - the physical traits of an organism controlled by the interaction of the gene with the environment.

population - a group of organisms belonging to the same species, either those living in a given geographical area or those dispersed throughout the world. Organisms in a population are capable of interbreeding.

quantitative traits - characteristics which exhibit continuous variation (like height, weight, or intelligence) and which arise from the interaction of many genes.