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QUESTIONS FOR DISCUSSION 



41.1. Apply the concept of the operon to the development of <^>T4. 



41.2. The work on nuclear transplantation by R. W. Briggs and T. J. King, J. A. 

 Moore, and others has proved that development sometimes involves irreversible 

 changes in the nucleus. Should such changes be termed mutations? Explain. 



41.3. In the snail Limnea peregra, self-fertilization of pure-line individuals whose shell 

 coils to the right, dextrally, or to the left, sinistrally, produces progeny all of 

 which coil as their parents. A cross of dextral 9 by sinistral $ yields all dextral 

 Fj which, when self-fertilized, yield all dextral progeny in F 2 - After self-fertiliza- 

 tion, however, % of the F 2 give rise to dextral F 3 and Vi of the F L , to sinistral F 3 . 

 The reciprocal cross, dextral 6 by sinistral 9, yields all sinistral F,. The F t 

 produces F;_» and F :{ phenotypically the same as the reciprocal cross. Give a 

 genetic explanation for these results. Are cytoplasmic genes involved? Explain. 



41.4. T. Yamada has found that isolated prospective ectoderm gives rise only to epi- 

 dermal cells when cultured in vitro in standard medium, but forms mesodermal 

 tissues if a protein fraction from bone marrow is added to the medium. To what 

 can you attribute these results? 



41.5. Suggest an explanation for the dedifferentiation which chondrocytes in vertebral 

 cartilage undergo when grown in vitro. 



41.6. Defend the following statement of J. D. Ebert (1963): "The principal theme, 

 coursing through and underlying research in embryology today, is the impact of 

 genetics on development. More than at any time in the past half-century, molec- 

 ular embryology is clearly the logical extension of molecular genetics." 



41.7. What conclusions can you draw from the following evidence concerning Down's 

 syndrome as found in the Victoria region of Australia: The incidence of the 

 syndrome varies year by year, with peaks occurring about every five years; about 

 40% of the cases are clustered geographically, more occurring in urban than in 

 rural areas. 



