Tetrad analysis helps to determine whether or not two genes are linked by using the four products of meiotic tetrads in Neurospora, yest and Chlamydomonas. This determination, which has been applied in genetic maps of eukaryotes, is critical to understand the mechanisms of heredity. Here, the relationship between ascus types and spore types was analyzed; a logic procedure of ordered tetrad analysis was suggested base on Mendelian laws, mechanisms of genetic recombination and mapping.