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Figure 4 | BMC Genomics

Figure 4

From: Deep ancestry of mammalian X chromosome revealed by comparison with the basal tetrapod Xenopus tropicalis

Figure 4

Proposed origin of X-added region of human X chromosome. A protochromosome (blue, left), present in the progenitor of Synapsida and Sauropsida, fused with several chromosomes (pink) to form the precursor of the eutherian X-Added Region (‘Pre-XAR’), now extant as most of opossum chromosomes 4 and 7. The Pre-XAR subsequently fragmented and fused with the therian X-Conserved Region (XAR and opossum X, yellow) to produce the eutherian X chromosome as well as with other partners (unshaded) contributing to autosomes. Fusion partners of the proto-XAR in amphibian (green) and avian (orange) lineages are also shown.

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