Section JO — Developmental Genetics 



is always evident. Anteroposterior, oblique, and 

 lateral types occur with equal frequency. 



Certain gynanders with female head and male 

 abdomen took a blood meal, then died when the 

 midgut broke open, presumably because the male 

 gut is not adapted to blood feeding. Conversely, 

 gynanders with male head and female body 

 attempted to copulate with females. One bilateral 

 gynander had components of external genitalia 

 from both sexes, one spermatheca (three in 

 females) and two ovaries, one of which contained 

 testicular tissue and mature sperm. 



In anterior-posterior gynanders with female 

 head and male abdomen, normal spermatogene- 

 sis occurs. Several of these individuals were 

 crossed to normal females, using the forced 

 copulation technique. In crosses using genetic 

 markers on all three linkage groups, the markers 

 were recovered in expected frequencies in the 

 F1-F3 generations. Moreover, sex ratio was nor- 

 mal and no additional gynanders were recovered. 

 Fi larvae had normal chromosome complements. 

 Thus, it seems unlikely that these gynanders are 

 produced through abnormal chromosome segre- 

 gation. 



Crosses with markers have demonstrated that 

 gynanders have different gene complements in 

 their male and female parts. It seems probable 

 that gynanders in A. aegypti are produced by 

 fertilization of a binucleate egg or an egg and a 

 polar body by two sperms. 



Supported in part by Atomic Energy Com- 

 mission Research Contract AT (ll-l)-38 and 

 NIH Grant No. AI 02753-04. 



1 0.10. The Influence of Temperature and X-rays on 

 the Sex of Carausius morosus Br. L. P. Pun- 

 acker (Groningen, The Netherlands). 



The stick insect Carausius morosus Br., native 

 to India, reproduces parthenogenetically in 

 Europe. However, <$<$ may appear spontaneously 

 (0.5 per cent $$ at 16°-20° C) but apparently 

 have no sexual function. Sexually aberrant 

 individuals showing gynandromorphy and/or 

 intersexuality are also found at frequencies of up 

 to 2 per cent. Progeny, if produced, are pheno- 

 typically normal. 



Eggs treated with higher temperatures gave 

 more aberrant individuals. Incubation at 25°- 

 27°C gave practically 100 per cent abnormals. 

 Temperature shock of 40° or 45 °C for two hours 

 also induced abnormals, the percentages depend- 

 ing upon the temperature and the stage treated. 

 Early stages (especially the stage at which the 



embryonal layers and appendages are developed) 

 were most sensitive with maximum percentages 

 of abnormals being 9 and 32 per cent at 40° and 

 45° respectively. 



Early embryonic stages are also sensitive to the 

 action of X-rays. Eggs receiving doses of lOOOr, 

 2000r, 4000r, 8000r, produced up to 60 per cent 

 abnormals. Only the first two series gave adults. 

 The progeny of these treated individuals showed 

 an increased number of $<$ dependent upon the 

 dose and the stage treated. $$ treated intheol- 

 est embryonic stages were most sensitive and 

 gave up to 26 per cent $$ in their progeny. 



<$<$ (spontaneously arising in control cultures) 

 have one heterochromatic sex-chromosome 

 compared with the two similar but euchromatic 

 chromosomes possessed by all $$ (2n = 66?). 

 Spermatogenesis is abnormal in both meiotic 

 divisions (precocious segregation or division, 

 lagging, non-disjunction, bridges), though normal 

 bivalents are found. Karyological investigations 

 indicate that interspecific hybridization may 

 have taken place in this species and this may 

 account in part for the lability of the sexual 

 phenotype. 



10.11. An Embryonic Lethal with Reversed Polarity 

 in Drosophila melanogaster. Alice Louise 

 Bull (Wellesley, U.S.A.). 



An inherited disturbance in egg polarity has 

 been observed in three related inbred lines of 

 Drosophila melanogaster, the parental line and 

 two others separated 176 and 191 generations 

 before the abnormality was discovered. Normal 

 winged female flies from these stocks, heterozy- 

 gous for a double inversion second chromosome 

 with markers CyL 4 sp 2 and an unmarked second 

 chromosome, produce embryos which develop 

 a second larval abdomen anteriorly and in 

 mirror-image symmetry to the normal abdomen. 

 The reversed posterior end consists of four 

 terminal abdominal segments with normal 

 posterior spiracles. The hindgut and Malpighian 

 tubules are present. The central internal region 

 of the embryo is characterized by an undiffer- 

 entiated sac connecting the two hindguts. 



Although symmetrical bicaudal embryos are 

 rare in an egg collection, other embryos showing 

 partial reversal of symmetry are found. In these 

 one to three terminal segments connect to a 

 normally oriented posterior end of varying 

 length. Still other embryos have normal sym- 

 metry, but exhibit disturbances in the formation 

 of the cephalopharyngeal apparatus. 



The occurrence of abnormal embryos (ap- 

 proximately 2-13 per cent) is always accompanied 



172 



