key concept 19.2 Gene Expression Differences Determine Cell Fate and Cell Differentiation

The fertilized egg undergoes many cell divisions to produce the many differentiated cells in the body (such as liver, muscle, and nerve cells). How can one cell produce so many different cell types? Determination occurs in two ways:

  1. Cytoplasmic segregation (unequal cytokinesis). Factors that play important roles in setting up the signaling cascades that orchestrate the major events of development may be unequally distributed in the cytoplasm of the egg, zygote, or precursor cell. After cell division, one or more of these factors, generally called cytoplasmic determinants, end up in some daughter cells or regions of cells, but not others.

  2. Induction (cell-to-cell communication). A factor is actively produced and secreted by certain cells to induce other cells to become determined.

focus your learning

  • Polarity may take place early in development, even within the fertilized egg.

  • Induction, whereby one part of the embryo signals another part to develop in a specific way, is exemplified by the development of the vulva in a nematode.

  • Cell differentiation during development involves changes in gene expression, as shown by the activation of the transcription factor MyoD in muscle differentiation.