Showing papers on "Pleiotropy published in 1987"

Quantitative genetics and fitness: lessons from Drosophila

Abstract: This paper examines patterns of heritability and genetic covariance between traits in the genus Drosophila. Traits are divided into the categories, morphology, behaviour, physiology and life history. Early theoretical analyses suggested that life history traits should have heritabilities that are lower than those in other categories. Variable pleiotrophy, environmental variation, mutation and niche variation may, however, maintain high heritabilities. In Drosophila the heritabilities of life history traits are lower than morphological or physiological traits but may exceed 20 per cent. The pattern of variation in the heritability of behavioural traits is similar to that of life history traits. Genetic covariance between morphological traits and between morphological and life history traits are all positive but those between life history traits have variable sign. Negative covariance between traits supports the variable pleiotropy hypothesis but other factors such as environmental heterogeneity, or mutation cannot be excluded.

The dynamics of sexual selection and its pleiotropic effects

Abstract: Since Darwin's formulation of the theory of sexual selection a number of population biologists have developed models that explore the genetic consequences of his theory. In all these models it is assumed that two forces act to counterbalance the runaway process of sexual selection. That is, female preference for a certain male character tends to select for extreme forms of that character until natural selection exerts its forces to maintain the optimum male phenotype that is able to survive in its environment. In this paper, an alternative explanation for the origin of secondary sexual characters is proposed. It is suggested that polymorphism in secondary sexual characters may be maintained not as a direct result of selection for these characters but by being either linked to or as pleiotropic effects of some other feature of the mate recognition pattern. While there are no genetic data to support these observations inDrosophila at this time, there appears to be compelling evidence that mating success is not wholly dependent on the presence of these characters.

Speciation via sexual selection versus adaptive evolution in Hawaiian Drosophila.

Abstract: With perhaps a thousand species present in the endemic fauna, the Hawaiian Drosophilidae represents one of the most striking examples of explosive adaptive radiation known in the animal kingdom. However, there is mounting evidence that it is shifts within the sexual environment that are more important in the speciation process. Classical concepts of sexual selection theory are reviewed and some new ideas regarding the role of sexual selection in the origin of secondary sexual characters are presented. It is suggested that there is a range of mating types in both sexes and that differential selection between the two sexes, i.e. selection for males with superior mating ability and for less discriminant females, results in the maintenance of an optimum behavioural phenotype in the population. It is further suggested that the dynamics of the sexual selection process and the effects of pleiotropy play a significant role in levels of genetic variability in a single interbreeding population.

Doubled haploids for detecting pleiotropy and linkage of genes controlling two characters

Abstract: A new method was developed for detecting pleiotropy and linkage of genes controlling two characters. It employs doubled-haploid lines derived from diallel crosses and permits quantification of pleiotropic effects. The method was used to study genetic correlations between five pairs of four characters (heading date, plant height, the number of spikes per hill, and grain yield) in seven varieties of barley. Results suggested that pleiotropy was present in all five pairs of characters and linkage in four pairs of characters. Key words: barley, haploids, pleiotropy, linkage.