Genetic variation is stored in a populationâs gene poolâthe combined. alleles of all of the individuals in a population. Different combinations of. alleles in a gene pool can be formed when organisms mate and have offspring. Each allele exists at a certain rate, or frequency.
Also found in: Wikipedia. cosÂ·tal surÂ·face. the surface of certain structures that face the ribs; they are the costal surfaces of the lungs (facies costalis pulmonis [TA]) and the scapula (facies costalis scapulae [TA]).
Functions include secretion and absorption (located in small ducts of glands and kidney tubules). Simple columnar epithelium â is a single layer of tall, closely packed cells that line the digestive tract from the stomach to the rectum. Functions include absorption and secretion.pithelial tissue is a sheet of cells that covers a body surface or lines a body cavity.