Recent Origin of Dioecious and Gynodioecious Y Chromosomes in Papaya. Yu, Q., Navajas-Pérez, R., Tong, E., Robertson, J., Moore, P., H., Paterson, A., H., & Ming, R. Tropical Plant Biology, 1(1):49-57, 2008.
Recent Origin of Dioecious and Gynodioecious Y Chromosomes in Papaya [pdf]Paper  Recent Origin of Dioecious and Gynodioecious Y Chromosomes in Papaya [link]Website  abstract   bibtex   
Sex of dioecious and gynodioecious papayas is controlled by two slightly different Y chromosomes, Y for males and Yh for hermaphrodites. All combinations of the Y and/or Yh chromosomes are lethal. We investigated the features of paired dioecious X- and Y-specific bacterial artificial chromosomes (BACs) and compared their sequen- ces to corresponding gynodioecious X- and Y-specific BACs. Numerous chromosomal rearrangements were detected between the X- and Y-specific BACs, including inversions, deletions, insertions, and duplications. DNA sequence expansion was documented on the Y BAC. Dioecious and gynodioecious X-specific BACs were virtually identical. The Y- and Yh-specific BACs shared high degree of DNA sequence identity, but local chromo- somal rearrangements were detected, as the consequence of suppression of recombination in the male specific region and the isolation of Yand Yh chromosomes enforced by the lethal effect. Analysis of sequence divergence between three dioecious X and Y gene pairs resulted in the estimated ages of divergence from 0.6 to 2.5 million years, reinforc- ing the hypothesis of a recent origin of the papaya sex chromosomes. The estimated age of divergence between Y and Yh chromosomes was approximately 73,000 years for Gene 5. Our findings indicate that Y and Yh chromosomes evolved from a common ancestral Y chromosome, possibly prior to the origin of agriculture. The existence of a hermaphroditeYh chromosome is less likely to have resulted from human selection as once suggested.

Downloads: 0