Diploid. (1) The number of chromosomes found in the zygote. (2) An organism having two sets of chromosomes.

Diplomats. Diploid state of an organism, ending with meiosis

Diplopoda. Millipedes. A class of Arthropoda.

Diplospondyly. The state in which organisms have two vertebrac in each body segment, as in the tails of some fish.

Diplotene. Stage in prophase of first division of meiosis, Following pachytene, in which pairs of chromatids derived from homologous chromosomes begin to separate from each other except at certain points of connection (chiasmata) Where interchange occurs between chromatid segments (crossing-over).

Disaccharide. A sugar, a compound of two monosaccharides. The biologically important disaccharides have 12 carbon atoms (formed from two hexoses), e.g. sucrose, maltose, lactose.

Displacement activity. An activity shown by an animal that appears to be irrelevant to its situation. Displacement activities are frequency observed when there is conflict between opposing tendencies. For example, birds in aggressive situations, in which there are simultaneous tendencies to attack and to flee, may preen their feathers as a displacement activity.

Distal. (1) Farthest from the point of attachment. (2) Of the part of a chromosome arm, which is further from the centromere than another part.

Diverticulum. Blind-ending tubular or sac-like out pushing from a cavity.

Dizygotic Twins (Fraternal Twins).
Twins developed as result of simultaneous fertilization of two separate ova. Such twins are genetically no more alike than other siblings.