FURTHER EVIDENCE THAT THE CHROMOSOME BREAKAGE FACTOR IN DROSOPHILA ROBUSTA INVOLVES A MATERNAL EFFECT
1963; Oxford University Press; Volume: 48; Issue: 9 Linguagem: Inglês
10.1093/genetics/48.9.1231
ISSN1943-2631
Autores Tópico(s)Silkworms and Sericulture Research
ResumoFORTY spontaneous chromosomal aberrations in Drosophila robusta in the laboratory were observed over a 15-month period (LEVITAN, 1962). All except two of the aberrations were found in crosses involving several generations of a certain laboratory stock. Wherever discrimination was possible, it was noted that the aberrations appeared in crosses involving females from this stock but not in crosses involving males from it, suggesting that induction of the aberrations depended on a maternal effect. In the next 15 months, 425 additional new aberrations have appeared, most of them during a series of crosses designed to test this hypothesis more accurately. The results of these experiments, to be described in this paper, confirm the maternal effect projected from the initial data. METHODS These experiments followed the same basic methodology as previous work, namely, testcrossing individuals of unknown karyotype to homokaryous stock-flies and studying salivary gland smears of their larval offspring. In this series, however, the identification of aberration inducers and the rate of aberration induction was to be the primary aim of the experiment, identification of unknown karyotypes secondary. It was hoped to avoid thereby the following defects which impaired the usefulness of the earlier crosses (LEVITAN 1962) for building a strong hypothesis concerning the aberration inducing property: ( 1 ) The small numbers and heterogeneity of the tested individuals (the unknown karyotype). These consisted of small samples from a number of artificial and widely separated natural populations, hence the possibility existed that the sample crossed to stock females was accidentally biased toward certain susceptible genotypes. (2) A variable number of stock flies were used per analysis cross. As many as five stock flies were used per cross when many were available, whereas other crosses each received but a single stock fly. The records indicated only which stocks, not how many flies from the stock, were used in the crosses, hence the possibility existed that more flies were consistently used in the crosses using stock females. (3) Analyses were generally stopped at the minimum number of larvae needed to determine the karyotype of the “unknown” parent. From some crosses cells from two larvae were seen, whereas in others ten or more were studied, with obvious oppor
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