Investigation of the inheritance of RAPD loci in Daphnia Pulex

Saunders, Barbara Ann (1998) Investigation of the inheritance of RAPD loci in Daphnia Pulex. Masters thesis, Memorial University of Newfoundland.

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Abstract

Inheritance and linkage of RAPD (randomly amplified polymorphic DNA) genetic markers were assessed in Daphnia pulex. Genetic markers are a useful addition to studies in areas of Daphnia biology, such as in investigations of population genetic structure and in estimating levels of gene flow between populations, that have been largely dominated by allozyme analyses. Daphnia pulex are freshwater Cladocerans that are ideal organisms for breeding studies because of their cyclical parthenogenetic mode of reproduction. Therefore, the inheritance of the genetic markers, generated using the RAPD molecular technique, can be examined in parent and progeny. In this study, crosses were made among ten clones from two Daphnia populations in southern Ontario. The percentage of hatched eggs in the F₁ ranged from 0-44.4%, with a survival rate to the production of first brood ranging from 40-100%. Four of the 18 interclonal crosses had sufficient F₁ sample sizes for examination using the RAPD technique. Eighty-one RAPD loci, both monomorphic and polymorphic, were scored (present or absent for each individual) and fifty of these loci were unique (some RAPD loci were present in individuals in more than one cross). Eighty-two percent of the RAPD loci were inherited according to the Mendelian segregation ratios of 1:1 or 3:1. Twenty-six of 29 loci conforming to 1:1 ratios were further examined for linkage to each other, but no linkage was found. However, linkage as tight as approximately r = 0.30 may not be detected because of small sample size (N =21- 47). Overall, the RAPD technique was successful in generating 46 segregating genetic markers for Daphnia pulex. Additional markers that are shown to be inherited in a Mendelian fashion may lead to detection of a marker linked to a gene of interest in Daphnia, such as the meiosis suppressor gene, and in future studies of variation in natural populations of Daphnia.

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