ICSI
See intracytoplasmic sperm injection.

Identical twins
See monozygotic twins.

Ideogram
See karyogram.

Imaginal disc
A mass of cells in the larvae of Drosophila and other holometabolous insects that gives rise to particular adult organs, such as antennae, eyes or wings.

Imbibition
(L. imbibere, to drink) 1. The absorption of liquids or vapours into the ultramicroscopic spaces or pores found in materials. 2. The initial water uptake by seeds starting germination.

Immune response
The processes, including the synthesis of antibodies, that are used by vertebrates to respond to the presence of a foreign antigen. See primary immune response; secondary immune response.

Immunity
The state of relative insusceptibility of an animal or plant to infection by disease producing organisms or to the harmful effects of their poisons.

Immunization
The production of immunity in an individual by artificial means. Active immunization involves the introduction, either orally or by infection, of specially treated bacteria, viruses or their toxins so as to stimulate the production of antibodies.