The Genome of the Western Clawed Frog Xenopus tropicalis Page: 4 of 86
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developed into one of the most productive model systems for vertebrate experimental
However, X laevis has a large paleotetraploid genome with an estimated size of 3.1
billion bases (Gbp) on 18 chromosomes and a generation time of 1-2 years. In contrast,
the much smaller diploid western clawed frog, X tropicalis, has a small genome, about
1.7 Gbp on 10 chromosomes (3), matures in only 4 months and requires less space than
its larger cousin. It is thus readily adopted as an alternative experimental subject for
developmental and cell biology (Fig. 1).
As a group, amphibians are phylogenetically well-positioned for comparisons to other
vertebrates, having diverged from the amniote lineage (mammals, birds, reptiles) some
360 million years ago. The comparison with mammalian and bird genomes also provides
opportunity to examine the dynamics of tetrapod chromosomal evolution.
The X tropicalis draft genome sequence described here was produced from -7.6-fold
redundant random shotgun sampling of genomic DNA from a seventh generation inbred
Nigerian female. The assembly ((4), Tables S1-S3 and accession AAMC00000000) spans
about 1.51 Gbp of scaffolds, with half of the assembled sequence contained in 272
scaffolds ranging in size from 1.56 to 7.82 Mb. Of known genes, 97.6% are present in the
assembly, attesting to its near completeness in genic regions (4). Nearly two million
Xenopus ESTs from diverse developmental stages and adult tissues complement the
genome and enable studies of alternative splicing and identification of developmental
stage- and tissue-specific genes (4).
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Hellsten, Uffe; Harland, Richard M.; Gilchrist, Michael J.; Hendrix, David; Jurka, Jerzy; Kapitonov, Vladimir et al. The Genome of the Western Clawed Frog Xenopus tropicalis, article, October 1, 2009; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc831346/m1/4/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.