Prime Types in Datura

Abstract

The term "prime type" is applied to races which have some of their chromosomes modified in comparison with a standard race. Such prime types found in nature in 5 species besides D. stramonium are apparently the result of segmental interchange between non-homologous chromosomes. Those obtained in D. stramonium after radiation treatment are the result of both segmental interchange and simple translocation. Under segmental interchange is included the limiting case in which an exchange of humps only has taken place. In the heterozygous condition an ordinary segmental interchange induces a circle of 4 or more chromosomes; an exchange of humps induces a "necktie" of 4 chromosomes; a simple translocation induces a "kite-like" configuration of 4 chromosomes. Pollen abortion may or may not be associated with these configurations. Prime types are usually heterozygous when first found, being rendered homozygous later. The modified chromosomes are identified by crosses with appropriate testers, which are selected prime types previously analyzed by crosses with 2n+l secondaries. Eighty prime types have been rendered homozygous. Of these there are listed 53 which have had all or some of the ends of the modified chromosomes determined.