Evolutionary patterns among permo-triassic therapsids
Article Abstract:
Research into evolutionary patterns among permo-triassic therapsids is reviewed. Use of cladistic methods has shed light on the relationships within therapsids. Based on recent discoveries in South Africa, it appears that Gondwana, not Laurasia, was the center of origin and radiation for many early therapsids. Understanding of the relative importance of convergent evolution and homoplasy in the origin of mammals has been advanced by quantitative techniques. Synapsids, including therapsids, contain the bulk of tetrapod diversity, both in number of species and in abundance, from Early Permian to Middle Triassic and can thus give vital information on the nature of the Permo-Triassic terrestrial extinction. Mammal-like reptiles in fossil form are of interest here.
Publication Name: Annual Review of Ecology and Systematics
Subject: Environmental issues
ISSN: 0066-4162
Year: 2001
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Sex chromosome meiotic drive
Article Abstract:
Sex chromosome meiotic drive, which is the unequal transmission of X and Y chromosomes from individuals of the heterogametic sex, is discussed. Mean fitness in a population may be reduced when the population has driving sex chromosomes. Other possible results include intragenomic conflict between the X chromosome, the Y, and the autosomes. The intensity or mode of sexual selection may be changed. Sex chromosome drive could be an agent of species-level selection. Sex chromosome drive, or its genetic equivalent, occurs in mammals, plants, and flies.
Publication Name: Annual Review of Ecology and Systematics
Subject: Environmental issues
ISSN: 0066-4162
Year: 2001
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The units of selection on mitochondrial DNA
Article Abstract:
Research into the units of selection on mitochondrial DNA (mtDNA) is reviewed with coverage of advances in population genetics, evolution of mtDNA, and transmission genetics. Metabolic properties of mitochondria make them highly mutagenic environments, and the mutational pressure brings mtDNA variation, that is, heteroplasmy, into the cytoplasmic population of cell lineages especially prone to mutational decay. Deleterious mutations are common in mtDNA evolution, based on neutrality test results.
Publication Name: Annual Review of Ecology and Systematics
Subject: Environmental issues
ISSN: 0066-4162
Year: 2001
User Contributions:
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