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]).
Most commonly the term is applied to the internal surface of the stomach (gastric rugae). The function of the rugae is to allow the stomach, or other tissue, to expand when needed. When the stomach is not full, the rugae are folds in the tissue. However, as the stomach fills it expands by unfolding the rugae.