Serial transplantation of embryonic nuclei.

Abstract

Over the past many years genetical research has revealed large numbers of gene effects on cell differentiation. These are usually effects on the final phases of differentiation, but may also be manifested at early developmental stages (Gluecksohn-Waelsch, 1954; Hadorn, 1948, 1956; Poulson, 1945; and others). In principle, the analysis of these effects depends upon the permanent alteration or deletion of a chromosome segment, and the subsequent detection of a change in differentiation—usually a deficiency. The evidence so obtained permits the conclusion that a particular gene or gene set is required for a particular type of differentiation to proceed normally. However, in general it leaves unanswered the questions which are of greatest concern to students of development. First, the genetic evidence as yet provides no explanation of the orderly segregation of cell types during development—of the fact that a given gene comes to have one effect in one part of the...