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The high frequency of recessive lethals on a segment of
the second chromosome with high inversion frequency
challenged a previously suggested role of the
chromosome inversion in maitaining sets of coadapted genes
in the nature populations of Drosophila albomicans. A
hypothesis to account for the high frequency of both
recessive lethals and the inversion heterozygosity was
then proposed. After two years investigating Wulai and
Guantzling nature populations of D. albomicans, we found
that In(2L)B1D5 heterozygosity reached 0.462 and the
recessive lethals between this section reached 0.436, which
were much higher than other species of Drosophila. Comparing
with 0.1 to 0.4 of recessive lethal frequencies on the whole
length of second chromosome of D. melanogaster, the length of
In(2L)B1D5 in D. albomicans is only a quarter of that of
second chromosome. In other word, the lethal frequency in D.
albomicans is much higher than that in D. melanogaster. The
high frequencies of recessive lethals and chromosome
inversions tell us that the chromosome segments with
inversions in nature populations may not contain coadapted
genes, but they do carry more recessive lethals than those
without inversions. The accumulation of recessive lethals
causes the increase of inversion heterozygosity, and the
a genetic load of a population seems to be the real reason
for inversion heterosis.
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