Document Type

Thesis - Open Access

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Degree Name

Master of Science (MS)

Department / School



Observed segregation ratios for qualitative traits in tetraploid alfalfa have been interpreted on both disomic and tetrasomic modes of inheritance. In fact, some tetrasomic ratios cannot be distinguished from disomic ones (13) without intensive analysis. For quantitative traits, arbitrarily established segregation ratios in themselves are incapable of interpretation with respect to mode of inheritance. Progressive change and fitness in species depend upon continuous variation; analogously, it may be reasonably inferred that artificial plant improvement too, rests upon the exploitation of continuous variation. The alfalfa breeder, in particular, to complement his art with science, must be able to select superior plants with a minimum of error and then to combine such plants in the most effective numbers, and in the most efficient manner. He must then be able to predict the behavior of given combinations in advanced generations. Application of the methods of biometrical genetics to the solution of these problems depends first upon a knowledge of the mode of inheritance. The main objective of this thesis was to determine the mode of inheritance of quantitative traits in tetraploid alfalfa.

Continuous variation, however, can only be studied through the statistical properties of the population. For purposes of this investigation, therefore, a statistic was required that would be amenable to both theoretical and experimental determination. It needed to be one to which some test of significance could be applied. A final requirement was that it be a statistic with theoretically different values dependent upon mode of inheritance. These three requirements, rigorously adhered to, set the course of the investigation. The genetic intra-class correlation was found to fulfill these requirements satisfactorily in the analysis of first generation selfed (S1) families. In this thesis, therefore, we have sought to evaluate the mode of inheritance, whether disomic or tetrasomic, by means of the genetic intra-class correlation.

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South Dakota State University


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