For our take-home exam, one of the questions asked about mosaicism and regulation and the differences between the two. I was particularly interested with each mechanism's relation to cell-to-cell interactions and how these interactions imply how these mechanisms exist in the environment naturally.
Mosaicism is the mechanism in which a cell's fate is predetermined by factors it receives during each cleavage. This principle suggests that the mosaic mechanism would not require cell-to-cell interactions. More interestingly, no truly mosaic embryos are known to exist in the environment. Therefore, there must be some other mechanism that is used in order for cell differentiation and embryo development.
Regulation is the mechanism in which an embryo is able to continue developing normally regardless of any changes or destruction. In order to detect these changes, there must be some form of cell-to-cell interactions.
Although there are some organisms that develop as if there is no cell-to-cell interaction and with a predetermined cell fate, it is evident that this is not the only mechanism for development. However, it is important to note an experiment done by Wilhelm Roux that suggested mosaicism as a basis. While studying fertilized frog embryos, Roux destroyed one of the two cells after the first cleavage. The remaining cell developed into only half of an embryo. Therefore, he concluded that mosaicism must be the basis of development for this organism. With this experiment, it only seemed logical that mosaicism was a useful mechanism.
So, if there are no purely mosaic embryos in the environment, what type of mechanism other than mosaicism takes place within a frog? With Roux's experiment, it seems as though mosaicism is a clear answer for this embryonic formation. However, this is only the result because Roux left the killed cell attached, but the embryo did not recognize the cell as being nonfunctional. If the killed cell had been removed, the embryo would have gone through regulation in which it would have developed into a smaller, but normal embryo.
Therefore, regulation is a key mechanism in development. However, with the information presented in class and my own critical thinking, it was hard to come up with this as the answer. Now that I finished my take-home exam, I decided to look up the real 'best' answer for development and it seems as though regulation is it!