ABSTRACT
The species of Anastrepha are arranged into 17 intrageneric groups. Recently, it was proposed that two species of the striata group, Anastrepha striata and A. bistrigata, might be realocated to serpentina group. Anastrepha bistrigata and A. serpentina have an X1X2Y/X1X1 X2X2 sex chromosome system while A. striata has a XY/XX system. It was previously proposed that the karyotype of A. bistrigata could be derived from that of A. striata by an Y:A fusion, and that the karyotype of A. serpentina would be derived from another, hypothetical karyotype. In the present report sequential staining with DAPI and chromomycin A3 (CMA3), followed by C-banding, revealed that the C-banded heterochromatic blocks of the sex chromosomes of A. bistrigata have different affinities to fluorochromes in comparison to the chromosomes of A. striata, from which they have hypothetically derived. The chromosomes of A. serpentina show substantial differences in their cytochemical properties compared to their A. bistrigata and A. striata counterparts. The FISH technique showed that the ribosomal gene sequences are located in DAPI- or DAPI/CMA3-positive heterochromatic blocks of the sex chromosomes, one site on the Y chromosome and one site on the X chromosome (X1 in A. bistrigata and A. serpentina). The data suggest that the karyotype of A. striata and A. bistrigata could be derived from a common ancestral karyotype, while the A. serpentina karyotype probably has a distinct origin.
ABSTRACT
We found that the sex-ratio of an amphigenic strain of Sciara ocellaris varied widely from progenies with few males to progenies containing a larger proportion of males, with single-sex progenies being rare. The sex-ratio distributions were dependent on the temperature at which the stocks of flies were raised, with the sex-ratio distributions being symmetrical (i.e. about 50 percent males) at 18 °C and 20 °C while at the higher temperatures of 24 °C and 28 °C the distributions were skewed toward a high proportion of females with the mean proportion of males decreasing to about 30-37 percent per progeny. Temperature-shift experiments showed that high temperatures were effective only during the last stages of female pupal development plus a period after adult emergence, stages corresponding to oocyte maturation. When imagine females were exposed to temperatures as low as 12 °C the sex-ratio distributions of their progeny were skewed toward a high proportion of males per progeny. No differential fecundity was involved in these progeny sex-ratio modifications. Egg-to-adult survival was lower at 18 °C and 28 °C but no correlations with skewing in the sex ratio distributions were observed, indicating that modifications in progeny sex-ratio did not involve the differential survival of a particular sex.
ABSTRACT
Hibridizaçäo in situ de RNA ribossômico de Xenopus com os cromossomos politênicos de Sciara ocellaris mostrou que nesta espécie os cistrons ribossomais estäo restritos à extremidade proximal do cromossomo X, regiäo onde um grande nucléolo é usualmente formado. Análise autorradiográfica da incorporaçäo de uridina tritiada nos cromossomos, após curta incubaçäo das glândulas salivares em meio de cultura, mostrou que os nucléolos e outras bandas ativas dos cromossomos marcaram-se intensamente ao contrário do resto dos cromossomos que mostraram pouca incorporaçäo. No nucléolo, os gräos de prata mostraram-se agrupados em pequenas subunidades com forma de cenoura e dispostas em fita. O comprimento axial dessas subunidades varia de 1,8 a 3,0 um. Conclui-se que essas subunidades representam cistrons ribossômicos em atividade. Existem, em média, cerca de 81 dessas subunidades por nucléolo. Numerosos micronucléolos säo vistos espalhados pelos nucleos, muitos dos quais associam-se a numerosas bandas ao longo dos cromossomos. Nossos resultados indicam que esses micronucléolos näo säo sintetizados nessas bandas cromossômicas mas representam subunidades nucleolares destacadas do nucléolo principal