Y

Yeast: Single-celled fungi that inhabit liquid or moist habitats and reproduce asexually by simple cell division or by the pinching of small buds of a parent cell.
Yeast artificial chromosome (YAC): A vector that combines the essential of a eukaryotic chromosome (an origin for DNA replication, a centromere, and two telomeres) with foreign DNA.
Yolk: Nutrients stored in an egg.
Yolk sac: One of four extraembryonic membranes that support embryonic development; the first site of blood cells and circulation system functions.