Publication Date


Document Type


First Advisor

Scheiner, Samuel M., 1956-

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences


Drosophila melanogaster; Chromosome abnormalities; Adaptation (Biology)


Phenotypic plasticity is an environmentally induced variation of a trait and is important to the evolution of the organism which exists under environmental conditions which fluctuate in either time or space. Many types of traits exhibit plasticity in response to many types of environmental variation. Phenotypic plasticity can be either adaptive or maladaptive. In the adaptive cases, the evolution of plasticity of a trait could be separate from the evolution of the trait itself, if the genetic mechanisms exist. In maladaptive examples of plasticity, trait canalization is accomplished by developmental or physiological plasticity. In order to study the genetic mechanism of phenotypic plasticity, the contributions of each chromosome to the traits thorax size and plasticity of thorax size as affected by temperature in Drosophila melanoqaster were measured. A chromosome extraction was performed to set each chromosome against a uniform background lacking genetic variation, provided by a stock of marked balancer flies. With regard to amount of plasticity, Chromosome I and the balancer stock showed no plasticity, the wild stock showed the greatest plasticity, and Chromosomes II and III were intermediate. Chromosome I showed significant genetic variation for thorax size at both 19°C and 25°C, but not for plasticity, while chromosome II showed significant genetic variation for plasticity, but not for thorax size. I tested the predictions of three models of the genetic basis of phenotypic plasticity: overdominance, pleiotropy, and epistasis. The results support the epistasis model, in agreement with earlier work. The amount of developmental noise was correlated with phenotypic plasticity at 25°C, in agreement with earlier work. A negative correlation was found at 19°C for chromosome II, contrary to earlier work.


Includes bibliographical references (pages [46]-51)


iv, 51 pages




Northern Illinois University

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