Navy blue. For other uses, see Navy blue (disambiguation). Navy blue is a very dark shade of the color blue. French sailor in dark blue uniform. Navy blue got its name from the dark blue (contrasted with white) worn by officers in the British Royal Navy since 1748 and subsequently adopted by other navies around the world.
Hybrid sterility is what results when individuals from two. different species are able to mate but their offspring is infertile, meaning that their. offspring are not able to reproduce. Because this occurs after the formation of the. zygote, this is a postzygotic isolating mechanism, not a prezygotic mechanism.
(Note, this is a preprint of an article published with some editorial changes in 1998 in Calow, P. (ed.) Encyclopaedia of Ecology and Environmental Management. Blackwell Press. pp. isolating mechanisms The reproductive characteristics which prevent species from fusing. Isolating mechanisms are particularly important in the biological species concept, in which species of sexual organisms are defined by reproductive isolation, i.e. a lack of gene mixture. Two broad kinds of isolating mechanisms between species are typically distinguished, together with a number of sub-types (modified from Mayr 1970): 1) Pre-mating isolating mechanisms. Factors which cause species to mate with their own kind (assortative mating). a) Temporal isolation. Individuals of different species do not mate because they are active at different times of day or in different seasons. b) Ecological isolation.