Section 10 — Developmental Genetics 



the lens from the ectoderm have been observed 

 in the experimental investigations on the eyes 

 of new-born rabbits and mice by one of the 

 authors (K. H. Degenhardt) using the techniques 

 of oxygen deficiency and X-irradiation damage at 

 particular stages of embryonic development. 



In these cases ruptures of the cornea, anterior 

 synechia, aplasia of the Decemet membrane 

 in the region of synechia, disintegration of the 

 fibres of the lens, aphakia, coloboma, microph- 

 thalmia and other known derangements were 

 observed. These malformations of the cornea, 

 iris and lens are to be considered as the beginning 

 of a teratological series of which the above 

 mentioned derangements of the human eye are 

 the most severe. If the animals had been allowed 

 to live longer secondary reparative changes 

 would have caused a scarred closure of the 

 rupture of the cornea and special changes of the 

 iris and the lens, as have been observed in 

 human eyes. This hypothesis is supported by the 

 condition of a rabbit eye, in which the rupture 

 of the cornea was already scarred. In human 

 beings the long duration of intrauterine develop- 

 ment prevents the observation of the early 

 stages of this special categoiy of eye defects. 



We think disturbances of inductive relation- 

 ships between the optic vesicle and the ectoderm, 

 initiated experimentally by oxygen deficiency 

 or by X-irradiation, are responsible. 



10.42. Response to a Teratogen of Mice Heterozygous 

 for Anophthalmia. Sidney L. Beck (Ann 

 Arbor, U.S.A.). 



Normal-eyed female ZRDCT-N (>) and C57BL/ 

 10 mice were mated with their own strain or 

 Anophthalmic (ZRDCT-An) males. Pregnant 

 mice were injected on the 7th, 8th and 9th days 

 post coituin with 0.25 cc. of 0.3 per cent trypan 

 blue ( 2 ), sacrificed during the 18th day of gestation 

 and examined for total implantation sites. Living 

 fetuses were examined for eye defects. Unilateral 

 and bilateral anophthalmia and various degrees 

 of microphthalmia on one or both sides were 

 found. 



The ZRDCT-N x ZRDCT-An matings 

 produced many more defective progeny than the 

 ZRDCT-N x ZRDCT-N (P < 0.001); mortality 

 was higher among the pure line matings (P < 

 0.001). These findings suggest that the presence 

 of the anophthalmic mutant (ey) in the heter- 

 ozygous state brings an animal close to a 

 threshold for defective eye development in a 

 cross of two closely related lines. 



Crosses of C57BL/10 x HL-ZRDCT-An 

 responded with a lower frequency of eye defects 



(not significant) and mortality (P < 0.001) than 

 C57BL/10 x C57BL/10. Here the most obvious 

 phenomenon among the hybrids was heterosis, 

 suggesting that differences in polygenic modifiers 

 between the two lines were stronger than, or 

 could mask the deleterious effect of, the single 

 dose of ey. 



In all cases the C57BL/10 crosses were affected 

 less than the corresponding ZRDCT-N crosses; 

 among all but C57BL/10 C57BL/10 there 

 were no spontaneously occurring eye defects. 

 In this latter group the teratogen doubled the 

 spontaneous frequency. In all crosses spon- 

 taneous fetal mortality was far lower (P < 0.001) 

 than mortality in stressed litters. 



1. Beck, Am. Zool. 1, 436, 1961. 



2. See Barber, Am. J. Ophtalmol. 44, 94, 1957 



10.43. The Effect of Cortisone on the Penetrance of 

 an Eye Mutant in the House Mouse. Muriel 

 J. Watney and James R. Miller (Vancouver, 

 Canada). 



The mutation elo which has recently occurred 

 in the C3H/MI mouse strain results in the 

 condition "eye-lids open at birth" (the mouse is 

 normally born with its eye-lids fused). This 

 mutant appears to be a simple autosomal 

 recessive with about 65 per cent penetrance in 

 homozygotes. In an attempt to increase this 

 penetrance, cortisone was administered to 

 pregnant females for several days prior to the 

 closure of the lids in utero which occurs during 

 the 17th day. Rather than increase the pene- 

 trance, the cortisone treatment resulted in a 

 significant decrease (to 4 per cent) in the frequen- 

 cy of the defect. On the basis of investigations 

 on the effect of cortisone on palate closure in the 

 mouse \ it is suggested that the cortisone 

 modifies the action of the elo gene through 

 mucopolysaccharides. 



1. Walker and Fraser, J. Embryol. Exp. 

 Morph. 5, 201, 1957. 



10.44. A New Gene Causing Cerebral Degeneration 

 in the Mouse. M. S. Deol and Gillian 

 M. Truslove (London, Great Britain). 



A new recessive gene (symbol cb) causing cere- 

 bral degeneration in the mouse has been dis- 



183 



