Genetic constitution and diversity in four narrow endemic redwoods from the family Cupressaceae |
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| Authors: | M Raj Ahuja |
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| Institution: | (1) 60 Shivertown Road, New Paltz, NY 12561, USA |
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| Abstract: | The genetic constitution and diversity of four relictual redwoods are discussed in this review. These include monotypic genera
of the family Cupressaceae: coast redwood (Sequoia sempervirens), giant sequoia (Sequoiadendron giganteum), dawn redwood (Metasequoia glyptostroboides), and alerce (Fitzroya cupressoides). All four species are narrow endemics, share a number of common phenotypic traits, including red wood, and are threatened
species. Fossil history suggests that the ancestors of redwoods probably originated during the Cretaceous and Tertiary periods
and flourished thereafter for millions of years. Towards the end of the Tertiary period began their decline and struggle for
existence that continued during the subsequent geologic upheavals and climate changes, until the survival of the present-day
redwoods in the current restricted locations in the world (USA, China, and South America). Although two species, Sequoiadendron and Metasequoia, are diploids (2n = 22), and the other two are polyploids: Fitzroya a tetraploid (2n = 4x = 44), and Sequoia a hexaploid (2n = 6x = 66); they all share the same basic chromosome number x = 11. The genome size in the hexaploid Sequoia is one of the largest (31,500 MB) in the conifers, while the genome sizes of diploid Metasequoia and Sequoiadendron are about one-third (~10,000 MB) of Sequoia. Genetic diversity in the redwoods is lower than most other gymnosperms, except in Sequoia, which seems to rank near the upper quarter of the coniferous forest trees. Genomic research is sparse in the redwoods, and
should be pursued for a better understanding of their genome structure, function, and adaptive genetic diversity. |
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| Keywords: | Redwoods Sequoia Sequoiadendron Metasequoia Fitzroya Fossil history Narrow endemics Genetic constitution Genetic diversity |
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