1. 1. Surani, M. A. H., Barton, S. C. & Norris, M. L. Nature 308, 548–550 (1984). 2. McGrath, J. & Solter, D. Cell 37, 179–183 (1984). 3. Surani, M. A. H., Reik, W., Norris, M. L. & Barton, S. C. J. Embryoi exp. Morph. 97 (Suppl.) 123–136 (1986). 4. Surani, M. A. H., Barton, S. C. & Norris, M. L. Cell 45, 127–136 (1986). 5. Barton, S. C., Surani, M. A. H. & Norris, M. L. Nature 311, 374–376 (1984). 6. Surani, M. A. H., Barton, S. C. & Norris, M. L. Nature 326, 395–397 (1987). 7. Searle, A. G. & Beechey, C. V. in Aneuploidy: Etiology and Mechanisms (eds Dellarco, V. L., Voytele, P. E. & Hollaender, A.) 363–376 (Plenum, New York, 1985). 8. Reik, W. et al. Eur. J. Immun. 17, 465–469 (1987). 9. Chapman, V., Forrester, L., Sansford, J., Hastie, N. & Rossant, J. Nature 307,284–286 (1984). 10. Rossant, J., Sanford, J. P., Chapman, V. M. & Andrews, G. K. Devl Biol. 117,567–573 (1986). 11. Rahe, B., Erickson, R. P. & Quinto, M. Nucleic Acids Res. 11, 7947–7959 (1983). 12. Jahner, D. & Jaenisch, R. Molec. cell. Biol. 5, 2212–2220 (1985). 13. Bird, A. P. Nature 321, 209–213 (1986). 14. Cattanach, B. M. & Kirk, M. Nature 315, 496–498 (1985). 15. Sanford, J., Forrester, W., Chapman, V., Chandley, A. & Hastie, N. Nucleic Acids Res. 12, 2823–2936(1984). 16. Ponzetto–Zimmerman, C. & Wolgemuth, D. J. Nucleic Acids Res. 12, 2807–2822 (1984). 17. Monk, M., Boubelik, M. & Lehnert, S. Development 99, 371–382 (1987). 18. Lock, L. F., Takagi, N. & Martin, G. R. Cell 48, 39–46 (1987). 19. Surani, M. A. H. in Experimental Approaches to Mammalian Embryonic Development (eds Rossant, J. & Pedersen, R. A.) 401–435 (Cambridge University Press, 1986). 20. Myers, R. H., Madden, J. J., league, J. L. & Falek, A. Am. J. hum. Genet. 34,481–488 (1982). 21. Klar, A. J. S. Nature 326, 466–470 (1987). 22. Feinberg, A. P. & Vogelstein, B. Analyt. Biochem. 137, 266–267 (1984). 23. Hecht, N. B., Liem, H., Kleene, K. C., Distel, R. J. & Ho, S. M. Devl Biol. 102,452–461 (1984). 24. Swain, J. L., Stewart, T. & Leder, P. Clin. Res. 35, 419A (1987).