In plants, retrotransposon copy numbers have been shown to vary from several hundreds to several million. The factors that regulate retrotransposon copy number are poorly known. A model by FLAVELL et al. (1997) proposing different effects of selection in genomes with low numbers of copia-like retrotransposons, against genomes with higher copy numbers of this retroelement, was tested. Non-synonymous to synonymous substitutions ratio (d N/dS), together with the frequency of occurrence of stop codons within the reverse transcriptase sequence of copia -like retrotransposons, were analyzed in relationship to copy number estimates of this retrotransposons. Evidence of purifying selection was detected in an enzyme directly involved in transposition. Genomes with less than 10,000 copia-like elements showed significantly smaller dN /dS ratios and fewer stop codons compared with genomes containing more than 10,000 copia-like elements. Genome size also appeared to be correlated with dN/dS ratios and frequencies of stop codons. Heterogeneity of copia-like retrotransposons was not related to dN/dS ratios. Copia-like retrotransposons with different copy numbers inside a single genome showed the same dN/d S ratios. The findings were discussed in relation to different possible selective scenarios in plants with low versus high retrotransposon copy number.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.33068 |
| Date | January 2001 |
| Creators | Navarro Quezada, Aura Rocio. |
| Contributors | Schoen, Daniel J. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Biology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001847634, proquestno: MQ77060, Theses scanned by UMI/ProQuest. |
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