Biology Glossary and Terms I | Comprehensive Guide |

Imaginal disc in the drosophila blastoderm

A group of undifferentiated cells that will develop into particular adult tissues and organs.

Immunoglobulins (igs)

Specialized proteins (antibodies) secreted by b cells that circulate in the blood and lymph and are responsible for humoral immune responses.


An experimental technique in which an antibody is allowed to bind to a specific target molecule in a solution, and then the antibody molecules, and all of the molecules bound to them, are collected (precipitated) from the solution.

Inborn error of metabolism

A biochemical disorder caused by mutation in a gene encoding an enzyme in a particular metabolic pathway.


Preferential mating between close relatives.

Incomplete dominance

The condition in which neither of two alleles is completely dominant to the other, so that the heterozygote has a phenotype between the phenotypes of individuals homozygous for either allele involved. Also called partial dominance.


A gaps in a sequence alignment where it is not possible to determine whether an insertion occurred in one sequence or a deletion occurred in another.

Induced mutation

Any mutation that results from treating a cell or organism with a chemical or physical mutagen.


A chemical or environmental agent that stimulates transcription of specific genes.

Inducible operon

An operon whose transcription is turned on in the presence of a particular substance (inducer). The lactose (lac) operon is an example of an inducible operon.


(1) stimulation of the synthesis of a gene product in response to the action of an inducer, that is, a chemical or environmental agent. (2) in development, the ability of one cell or group of cells to influence the developmental fate of other cells. Inferred tree a phylogenetic tree generated with molecular data from real organisms.

Initiation factor (if)

Any of various proteins involved in the initiation of translation.

Initiator protein

A protein that binds to the replicator, stimulates local unwinding of the DNA, and helps recruit other proteins required for the initiation of replication. Insertion sequence (is element) the simplest transposable element found in prokaryotes. An is element contains a single gene, which encodes transposase, an enzyme that catalyzes movement of the element within the genome. Insulator a DNA regulatory element, located between a promoter and associated enhancer, that blocks the ability of activators bound at the enhancer to stimulate transcription from the promoter.

Interaction variance (vi)

Genetic variation among individuals resulting from epistasis.

Intercalating agent

A chemical mutagen that can insert between adjacent nucleotides in a DNA strand.


Phenomenon in which the presence of one crossover interferes with the formation of another crossover nearby. Mathematically defined as 1 minus the coefficient of coincidence. Also called chiasma interference.

Intergenic suppressor

A mutation whose effect is to suppress the phenotypic consequences of another (primary) mutation in a different gene.

Intragenic suppressor

A mutation whose effect is to suppress the phenotypic consequences of another (primary) mutation within the same gene.


Transfer of genes across species barriers.


A segment of a protein-coding gene and its precursor mRNA (pre-mRNA) that does not specify an amino acid sequence. Introns in pre-mRNA are removed by mRNA splicing.


A chromosomal mutation in which a segment of a chromosome is excised and then reintegrated in an orientation 180° from the original orientation.