Richard Gordon wrote:
>How about some key refs to the genetic mosaic mechanism of bilateral
>asymmetry, for those of us not raised on fruit flies?
Here are some tidbits on mosaicism in Drosophila. Chemical mutagenesis of
sperm is known to result in a high proportion of mosaically recovered
mutations (Auerbach 1946; Lee 1976; Nissani 1977). This is probably due to
the fact that fertilization in Drosophila is gonomeric, i.e., both haploid
sperm nucleus and haploid fertilization nucleus of the egg undergo a
mitotic division before fusion (Heuttner 1924), and fusion is immediately
following the first mitotic anaphase. In contrast to chemical mutagens,
ionizing radiations are thought not to give rise to a high proportion of
mosaically recovered mutations (Lee 1976), although it is clear that
radiation damage in sperm is not repaired before fertilization (Muller
1940). Nevertheless, radiation-induced chromosome loss does occur
(reviewed by Hall, Gelbart and Kankel 1976). Differential DNA repair in
the two nuclei is probably a significant factor for chemically induced
mutations or radiation induced ones.
The fate of the products of the first division does not necessarily produce
mosaicism that is bilaterally symmetrical, but often it is (or maybe these
are the most easily recognized? Anyone know frequencies?).
Auerbach, C. (1946). Chemically induced mosaicism in Drosophila
melanogaster. Proc. Roy. Soc. Edinb. B62, 211-221.
Hall, J.C., Gelbart, W.M., and Kankel, D.R. (1976). Mosaic systems. In The
Genetics and Biology of Drosophila., Vol.1a, Ashburner, M., and Novitski,
E., eds. (New York: Academic Press), pp. 265-314.
Heuttner, A.F. (1924). Maturation and fertilization in Drosophila
melanogaster. J. Morph. Physiol. 39, 249-265.
Lee, W.R. (1976). Chemical mutagenesis. In The Genetics and Biology of
Drosophila, Vol.1c, Ashburner, M., and Novitski, E., eds. (New York:
Academic Press), pp. 1299-1341.
Muller, H.J. (1940). An analysis of the process of structural change in
chromosomes of Drosophila. J. Genet. 40, 1-66.
Nissani, M. (1977). On the interpretation of mutagenically induced
mosaicism in Drosophila. Genetics 86, 779-787.
I don't know the nature of the early lobster cleavages, so I don't know how
these Drosophila findings will relate.
Daniel F. Eberl ò_ó
Department of Genetics (...)
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