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When trying to solicit authors for this book it became apparent that the causal factors for heterosis at the physiological and biochemical level are today almost as obscure as they were 30 years ago.

The Predominance of species exhibiting genic male sterility and of species crosses exhibiting gene-cytoplasmic male sterility is due to the fact that for the male sterility expression in the former, mutation of nuclear genes is required, but in the latter, mutations of both nuclear and cytoplasmic genes are necessary.

In late 1971 we were involved in a study of the interaction of radiation with matter and were trying to use measurements of radiation fluorescence in biological molecules to indicate how radiation affected living cells.

Because of the great variety of problems which this genus presents to biologists, Oenothera belongs to the best-known genera of plants not used economically. It is further of great value for all those whose research topics are based on genetics, such as developmental and evolutionary biology.

The idea for this book was conceived by the late Dr. Irvine A. Dr. Watson's intention was to produce a very practical book that would provide wheat breeders with all of the information necessary to breed success fully for resistance to the three wheat rusts: leaf rust, stem rust, and yellow rust.

The aim of the monographs is to foster effective intra- and interdisciplinary communication between geneticists, and plant and animal breeders. This is to be achieved by publishing authoritative up-to-date texts; concise, but at the same time comprehensive, monographs, and multiauthor volumes on theoretical and applied genetics. The following broad fields of genetics and breeding are within the scope of the series: Evolutionary genetics Developmental genetics Population genetics Biochemical genetics Ecological genetics Somatic cell genetics Biometrical genetics Agricultural genetics Cytogenetics Mutation breeding Radiation genetics Breeding methodology Acceptable subjects for the Monographs on Theoretical and Applied Genetics are basic and applied aspects of genetic variation; genetic resources; genetic exchange and reproduction; mutagenesis; genotype-environment interaction; gene structure, regulation, action, expression and interaction; chromosomal and extrachromosomal inheritance ofeconomic traits, and genetic models and simulations. September 1975 The Editors Preface Meiotic configurations are looked at from a special point of view in this book: the extraction from them of the maximal amount of quantitative information of genetic interest. Although this requires a certain understanding of their origin and consequences, much of what is known about chromosomes and their for­ mation into the special structures collected under the rather indiscriminate term I "configuration", is not considered relevant for this purpose, and simply neglected.

A century of research on heterostylous plants has passedsince the publication of Charles Darwin's book "TheDifferent Forms of Flowers on Plants of the Same Species" in1877 summarizing his extensive observations and experimentson these complex breeding systems involving geneticpolymorphisms of floral sex organs.

Although only about 3 years have passed since the preparation of the original manuscript of this book for the Russian edition, the number of successful experiments on somatic hybridization of higher plants has doubled.

Mutation breeding has been introduced into modern plant breeding in the early 1940's. Many mutants with characters of agronomic interest cannot be utilized directly because of their unsatisfying yielding capacities, or of other negative traits which are partly due to the pleiotropic action of the mutant genes.

Recently three important conclusions have been derived (Davidson and Britten, 1979) which help to pose the problem in a new way: 1) Only a small part of single copy sequences of DNA is represented in nuclear RNA of a given type of cell or tissue: 10% to 20% in sea urchin embryos, 11 % in rat liver, 4% to 6% in Drosophila cell culture, etc.

The first part starts with an evaluation of the significance of the different pollination mechanisms for plant breeding and crop produc tion, describes modes of reproduction in higher plants and discusses ecology and dynamics of pollination.

The presentation is organized around the development of breeding from single-to multiple-option plans, from single to multiple traits, from single to mUltiple environ ments, and from single to multiple populations.

In most of the cases, backcross or modified backcross methods have been followed to utilize wild species, and thus numerous types of resistance and other economical attributes have been transferred in the recurrent parents.

An introductory discussion of basic chromosome structure andfunction preceeds the main text on the application ofcytogenetic approaches to the analysis of the manipulationof both the genetic make-up and the genetic transmissionsystem of plant breeding material.