紅果蠅階段性染色體進化
Date Issued
2000
Date
2000
Author(s)
張慧羽
DOI
892313B002031
Abstract
The neo-X and neo-Y chromosomes of
Drosophila albomicans were formed by two
fusion events of the ancestral sex and 3rd
chromosomes during evolution. The main
purpose of this study is to show
chromosomal selection forces involved
during evolution. Fortunately, D.
albomicans can produce fertile hybrids with
its sibling species, D. nasuta. Therefore, it is
possible to test our hypothesis of “stepwise
2
chromosome evolution”.
In our “stepwise chromosome evolution”
hypothesis, the new sex chromosome formed
by the first fusion event can be maintained
under a polymorphic condition in the
population for a long time waiting for the
occurrence of the second fusion event. The
two fused chromosomes will be fixed in the
population by selection forces.
This hypothesis can solve some of the
long lasting issues in the study of D.
albomicans evolution. For instance: the
hybrid populations established in our
laboratory maintained polymorphic for at
least twenty generations, whereas the hybrid
populations established in Dr. Ranganath's
laboratory in India soon became fixed. If our
“stepwise chromosome evolution” hypothesis
is correct, this phenomenon is apparently due
to different initial conditions.
In order to test this hypothesis, we had
established four different types of
populations to represent the two stages of
chromosome evolution. They were fixed
ancestral X with two kinds of Ys, fixed
ancestral Y with two kinds of Xs for stage I,
and fixed neo-X with two kinds of Ys, fixed
neo-Y with two kinds of Xs for stage II. The
result of that study supported our hypothesis
indirectly, but there still exists some
uncertainty between the two stages, i.e., in
stage II, the populations were initiated from a
condition that the first fused chromosome
had been fixed. However, the data only
supported that polymorphism can be
maintained at stage I. Therefore, we planed
to establish a population with all four types
of chromosomes simultaneously, and see if
the two fused chromosomes will go fixation
as we predicted. The result of two replicated
experiments revealed that karyotype
polymorphism exists in E1 hybrid population
after long-term cultivation, but the 3-X and
3-Y chromosomes are excluded rapidly after
20 generations. This unexpected result
accidentally showed that the meiotic drive,
which we tried to avoid in our experiments,
might play an important role in the
chromosome evolution of D. albomicans.
The investigation of the relationship between
meiotic driver and chromosome evolution of
this species is in progress.
Subjects
chromosomal evolution
Drosophila albomicans
D. nasuta
Robertsonian change
Publisher
臺北市：國立臺灣大學昆蟲學系暨研究所
Type
report
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