Structural analysis of Oenothera complexes

InOenothera species each functional gamete normally contains seven chromosomes, which together may be described as a gametic complex. Each species has two such complexes, either identical or different from one another. The differences are (1)structural , the chromosomes of two complexes differing in one or more interchanges, and (2)genic , the complexes differing in gene content. The present account deals principally with the first kind of difference. A complete and accurate analysis is a prerequisite for various kinds of genetic investigation ofOenothera . The seven chromosomes of each gametic complex are composed of fourteen end-pairing segments, no two of which are alike, and of seven middle pieces probably including the centromeres. The middle parts of the chromosomes have so far largely defied analysis. However, it is possible to specify and define each of the end-pieces, and therefore each chromosome in terms of them, on physiological grounds, namely, their property of pairing at meiosis. Owing to the interchanges by which complexes differ, different metaphase associations of chromosomes are produced at meiosis by the pairing of similar chromosome ends when different complexes are combined. Considerable advances in such cytological analysis of many complexes have been made, especially by Emerson and Sturtevant (1931, 1932), Emerson (1936) and Cleland (1935, 1937). Renner (1933, 1938) has made similar analyses by employing breeding chromosomes are linked in segregation.