Inbreeding: The breeding of genetically similar individuals e.g. bothers and sisters. This is bad. It promotes homozygosity and increases the chance of genetic disease.

​Incidence (incidence rate): Number of new cases of a particular disease in a population.

​Incomplete dominance: When two alleles both exert an effect. e.g. in the Human ABO blood groups, A and B are codominant over O.  

​Incubation period: The time taken for signs and symptoms to appear following entry of a pathogen  into a host organism.

Independent assortment: A key feature of meiosis, which separates the homologous chromosomes so that any one of a pair of alleles can pass into a gamete with one from any other pair.

​Index case: The first recorded case of a disease in an outbreak (endemic, epidemic or pandemic).

Induced Mutations: Mutation(s) caused by direct exposure to a known mutagen.

​Infection: The invasion of a host by a microorganism with subsequent establishment and multiplication of the agent. An infection may or may not lead to overt disease.

Insecticide: Chemical that kills insects.

Intensive farming: Production of high yields from a small land area.