Glossary of Coral Reef Terminology - Y

Y junction - in genetics, the point of active DNA replication where the double helix opens up so that each strand can serve as a template

Y linkage - in genetics, the rare inheritance pattern of genes found on the Y chromosome but not on the X

Y-organ - a gland situated near the external adductor muscles of the mandibleof some crustaceans that secretes the molting hormone

YAC (yeast artificial chromosome) - a vector used to clone DNA fragments from 300 kb to one megabase (unit of length for DNA fragments equal to one million nucleotides) in length. These clones can span large portions of the genome rapidly, but can be highly unstable

year class - fish of a given species spawned or hatched in a given year

yearling - a one-year-old individual in its second year of life

yeast - a single-celled fungus that reproduces by budding

yellow-band disease - a coral disease characterized large rings or patches of bleached, yellow tissue on Caribbean stony corals, although tissue loss is minimal (cm/yr). It affects the star corals, Montastraea annularis and M. faveolata and is widespread throughout the Caribbean region. No pathogen has been isolated. For more information and illustrations, see: http://www.coral.noaa.gov/coral_disease/yellow_band.shtml

yolk - nutritive material of an ovum, consisting of protein and fat, stored for the nutrition of an embryo or early larva

yolk cell - in a telolecithal egg (an egg in which the yolk is not distributed evenly, but concentrated in one region), the yolk cells are the cells formed when cleavage reaches the yolk region

yolk sac - a vascularized extra-embryonic membrane of amniote embryos that forms around the yolk of the egg cell in birds and reptiles. In mammals, the yolk sac membrane grows out around the empty blastocoel (blastula cavity) formed within the inner cell mass in the cleaving embryo. The blastocoel is renamed the yolk sac. In birds and reptiles, the blood vessels in its walls transport yolk nutrients to the embryo. In mammals, these vessels still form even though they don't supply nutrients to the embryo. They remain to form blood vessels in the digestive tract

yolk-sac larva - a fish larva which has already hatched from the egg but has not yet started feeding and still absorbs the yolk in the ventrally-attached yolk sac

young-of-the-year (YOY) - fish that are less than one year old; hatched during the spawning season