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Title: Population genetic studies of the S-locus gene family and other loci in self-compatible and self-incompatible populations of the plant Antirrhinum
Author: Gonçalves Paula Vieira, Cristina Alexandra
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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In this work the mating system of several populations and species of Antirrhinum were established in the glasshouse. Levels of DNA diversity were estimated based on cyc and fil1 nuclear genes. Both genes are shown to belong to gene families. In these gene families, some members are very similar, which makes difficult to determine orthology. In the cases where orthology is not a problem, low levels of nucleotide diversity were found. Therefore the effect of the mating system on genetic diversity could not be tested. An unexpected finding of very little divergence between several Antirrhinum species, Digitalis, and the more distantly related genus Verbascum was also found for genes of the cyc and fill gene families. The generality of this pattern was addressed by extending these studies to fil2, far, globosa and Adh genes. Evidence is shown that these genes are also members of gene families in Antirrhinum. For fil2, far, and globosa, very similar sequences were found in Antirrhinum and Verbascum. For Adh I could not determine orthology because repeated gene duplication and loss of elements in this gene family has occurred in the Antirrhinum and Verbascum lineages. Several hypotheses that could account for the low diversity and divergence are discussed. In Antirrhinum, self-incompatibility is controlled by a gametophytic system. The gene responsible for pistil self-incompatibility is the S-locus that encodes basic glycoproteins with ribonuclease activity. High levels of variability are observed, consistent with frequency-dependent selection. The putative targets of selection are those regions, such as the hypervariable regions of this gene, that may be involved in specificity determination. In order to gather evidence on whether these regions are hypervariable because they are the target of selection, or merely regions of relaxed selective constraint, we have partially sequenced Antirrhinum S-alleles and analysed their level and pattern of nucleotide diversity. Within each allelic type, low levels of diversity were observed. Similar alleles were found in self-compatible and self-incompatible species, suggesting that the Antirrhinum group evolved recently.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available