The origin and differentiation of the heteromorphic sex chromosomes Z, W, X, and Y in the frog Rana rugosa, inferred from the sequences of a sex-linked gene, ADP/ATP translocase |
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Authors: | Miura I; Ohtani H; Nakamura M; Ichikawa Y; Saitoh K |
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Institution: | Laboratory for Amphibian Biology, Faculty of Science, Hiroshima University, Japan. imiura@ue.ipc.hiroshima-u.ac.jp |
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Abstract: | Sex chromosomes of the Japanese frog Rana rugosa are heteromorphic in the
male (XX/XY) or in the female (ZZ/ZW) in two geographic forms, whereas they
are still homomorphic in both sexes in two other forms (Hiroshima and
Isehara types). To make clear the origin and differentiation mechanisms of
the heteromorphic sex chromosomes, we isolated a sex-linked gene, ADP/ATP
translocase, and constructed a phylogenetic tree of the genes derived from
the sex chromosomes. The tree shows that the Hiroshima gene diverges first,
and the rest form two clusters: one includes the Y and Z genes and the
other includes the X, W, and Isehara genes. The Hiroshima gene shares more
sequence similarity with the Y and Z genes than with the X, W, and Isehara
genes. This suggests that the Y and Z sex chromosomes originate from the
Hiroshima type, whereas the X and W chromosomes originate from the
Isehara-type sex chromosome. Thus, we infer that hybridization between two
ancestral forms, with the Hiroshima-type sex chromosome in one and the
Isehara-type sex chromosome in the other, was the primary event causing
differentiation of the heteromorphic sex chromosomes.
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