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. 2021 Jan 6;592(7856):756–762. doi: 10.1038/s41586-020-03039-0

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© The Author(s) 2020

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 2 — a, Genomic composition of the platypus sex chromosomes. From the outer to inner rings: the X chromosomes with the PARs (light colours) and SDRs (dark colours) labelled; the assembled Y chromosome fragments within SDRs showing the colour-scaled sequence divergence levels with the homologous X chromosomes; female-to-male (F/M) ratios of short sequencing-read coverage in non-overlapping 5-kb windows; F/M expression ratios (each red dot is one gene) of the adult kidney and the smoothed expression trend; and GC content in non-overlapping 2-kb windows. In addition, we labelled the positions on the X chromosome ring of the gametologue pairs that have suppressed recombination before the divergence of monotremes (‘shared’, orange triangles) or after the divergence (‘independent’, blue triangles). b, Homology between X and Y chromosomes of platypus. In particular, most of Y5 shows homology with X1 and X2, which suggests an ancestral ring conformation of the platypus sex chromosomes. We also labelled the position of the putative sex-determining gene AMH. The platypus silhouette is created by S. Werning and is reproduced under the Creative Commons Attribution 3.0 Unported licence (http://creativecommons.org/licenses/by/3.0/).