imprinting A type of behavior learned during a cer-
tain critical time in development that promotes the
learning of behavior and characteristics of the species
and is difficult to reverse, regardless of circumstances.
Anexample is the attachment behavior among birds to
the mother during the first few hours after hatching. In
genetics, it is when an allele at a particular locus is
inactivated or altered depending on whether it was
inherited by the mother or father.
inbreeding The production of offspring by closely
related parents with a high likelihood of carrying simi-
lar deleterious recessive mutations that may be
expressed in the phenotypes of the offspring. The
resulting populations may suffer a higher than average
incidence of recessive genetic disorders.
incest When two people too closely related have
intercourse, i.e., a parent and child, or two first
cousins. Usually socially prohibited.
incomplete dominance A type of inheritance where
the heterozygote that has two different alleles (one
dominant, one recessive) of a gene pair has a different
appearance (phenotype) compared with the homozy-
gous (identical alleles for a given gene) parents.
incomplete flower A flower lacking one of the four
major parts: SEPALs, petals, STAMENs, or CARPELs.
incomplete metamorphosis Part of a life cycle of
an insect where the nymph stage, or immature form,
resembles the adult after hatching and slowly changes
into the adult form through a series of molts; does not
have a pupa stage. Examples are grasshoppers (Oth-
optera), aphids, cicadas, and whiteflies. A form of
incomplete metamorphosis called gradual metamor-
phosis is when there is no pupal stage and the nymphs
look like the adults minus the wings. Unlike complete
metamorphosis, which has four stages (EGG,LARVA,
PUPA, and adult), incomplete metamorphosis only has
three (no pupa).
See alsoMETAMORPHOSIS.
IND Investigational new drug.indeterminate cleavage A form of cleavage found in
dueterostomes (e.g., chordates and echinoderms) where
each cell produced during early cleavage division has
the ability to develop into a complete embryo.indeterminate egg layer The ability to induce birds
to lay more eggs by removing or destroying eggs they
have already laid. Also called double clutching.indeterminate growth When an organism continues
to grow throughout its life span (ontogeny); character-
istic of plants.indeterminate inflorescence When the central part
of the flower is the last to open. Terminal flowers open
last and lower flowers open first.index fossils Abiologic method of time correlation
using commonly found fossils that are limited to a spe-
cific time span. For example, trilobites, though com-
mon in the Paleozoic, are not found before the
Cambrian period. Some lineages of fossil organisms
evolved rapidly, so that the vertical stratigraphic range
of the species was short but the species was
widespread. A dating technique to correlate the ages of
rocks in difference locations (biostratigraphy).
See alsoGEOLOGICAL TIME.indigenous An organism that is native and not intro-
duced in a specific environment with certain boundaries.
See alsoENDEMIC SPECIES.induced fit The change in the shape of an enzyme’s
active site to accommodate and bind firmly to the sub-
strate that enters the site.induction The process whereby one set of embryonic
cells influences the development of another set of
embryonic cells.174 imprinting