CONCEPTS IN BIOLOGY

PART III. MOLECULAR BIOLOGY, CELL DIVISION, AND GENETICS

9. Cell Division—Proliferation and Reproduction

9.6. Determination and Differentiation

The process of mitosis enables a single cell to develop into an entire body, with trillions of cells. A zygote is the original single cell that results from the union of an egg and sperm. The zygote divides by mitosis to form genetically identical daughter cells. Mitotic cell division is repeated over and over until an entire body is formed.

Although the cells in the mature body are the same genetically, they do not all have the same function. There are nerve cells, muscle cells, bone cells, skin cells, and many other types. The difference among cell types is not in the genes they possess, but in the genes they express (i.e., through epigenetics).

Determination is the cellular process of deciding which genes a cell will express when mature. Determination marks the point where a cell commits to becoming a certain kind of cell and starts down the path of becoming that cell type. When a cell reaches the end of that path, it is said to be differentiated. A differentiated cell has become a particular cell type.

Skin cells provide a good example of determination and differentiation. Some skin cells produce hair; others do not. All the body’s cells have the gene to produce hair, but not all cells do. When a cell starts to undergo the process of becoming a hair-producing cell, it is undergoing determination. Once the cell has become a hair-producing cell, it is differentiated. This differentiated cell is called a hair follicle cell (figure 9.18).

FIGURE 9.18. Determination and Differentiation

A cell starts as undetermined and undifferentiated. Specific genes are expressed to provide a cell its unique identity. Here, an undetermined cell goes through the process of determination to express the genes needed to be a hair follicle. When the process is complete and the hair follicle genes are expressed, the cell is differentiated.

9.6. CONCEPT REVIEW

17. What is the difference between determination and differentiation?