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Vol. 47 No. 1, 2008
The Fate of Neo-Sex Chromosomes in Drosophila albomicans-nasuta Hybrid
Populations
Yung-Yu
Yang1, Chun-Yen Lee11,
Yi-Hua Yang1, Shu-Ping
Huang1, Te-Pin Chang1,
and Hwei-yu Chang1,2,*
1Department
of Entomology, National Taiwan University, Taipei 106, Taiwan
2Research Center for Biodiversity, Academia Sinica,
Nankang, Taipei 115, Taiwan
Yung-Yu Yang,
Chun-Yen Lee, Yi-Hua Yang, Shu-Ping Huang, Te-Pin Chang, and Hwei-yu
Chang (2008) Drosophila albomicans (2n = 6), bearing a pair of neo-sex
chromosomes, can be crossed to an allopatric sibling species D. nasuta (2n = 8). We previously
proposed a“stepwise chromosome evolution” hypothesis to elaborate 2
stages in the karyotype evolution of D.
albomicans derived from the ancestral nasutalike state.
The 1st stage included the formation and maintenance of the fused 3-X
chromosome, and the 2nd stage included the fusion of 3-Y and the
increased frequency of both fused chromosomes. The 2-stage model
is supported by a previous study using experimental populations with
either the X- or Y-type sex chromosome fixed. In this study, we
attempted to explore the fates of sex chromosomes in populations
initially consisting of all 4 types of sex chromosomes (i.e., the
derived 3-X and 3-Y, and the ancestral X and Y). Our present
results revealed that the 3-X chromosome is capable of reaching a high
frequency as 3-Y reaches fixation, and the frequency of 1 neo-sex
chromosome depends on that of the other in the same population.
In another set of experimental populations, the existence of a meiotic
driver located on the neo-X chromosome showed no significant effect on
the fate of this chromosome. The efficacy of extrapolating these
results obtained from hybrid populations to the initial chromosomal
dynamics of D. albomicans is
discussed.
Key words: Evolution, Fused chromosome,
Karyotype, Meiotic driver.
*Correspondence: Tel: 886-2-33665575. Fax:
886-2-27325017. E-mail:hwei@gate.sinica.edu.tw; hwei@ntu.edu.tw
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