In yet another unusual characteristic of the Platypus, sex determination does not arise from a simple combination of one X and one Y chromosome. Grutzner et al (2004) demonstrate that the platypus has five male-specific chromosomes (Y chromosomes) and five X chromosomes present in one copy in males but in two copies in females (X chromosomes). At meiosis these ten chromosomes form an alternating pattern XYXYXYXYXY and XXXXXXXXXX to then segregate into sex determining sperm each with 5X or 5Y chromosomes.
- Grützner, F., Rens, W., Tsend-Ayush, E., El-Mogharbel, N., O’Brien, P. C. M., Jones, R. C., Ferguson-Smith, M. A., et al. (2004). In the platypus a meiotic chain of ten sex chromosomes shares genes with the bird Z and mammal X chromosomes. Nature, 432(7019), 913-7. Macmillian Magazines Ltd. doi:10.1038/nature03021
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