Parthenogenesis, homozygosity, and cloning in mammals.

The numerous strategies for reproduction, sexual and asexual, that have evolved, suggest experimental designs for altering the reproduction of any particular species. The ability to culture and manipulate mammalian eggs and embryos in vitro provides the technological basis for experimentally altering the reproduction of mammals and can lead to the generation of new and useful genotypes. All of these advances, however, are restricted by our lack of understanding of the chromosomal mechanisms by which genes are regulated during the course of cell differentiation. An attractive hypothesis postulates that programs of gene regulation during development are based upon topographic interactions among chromosomes in the interphase nucleus and that these interactions in turn require an appropriate positioning of regulatory DNA throughout the genome.