Heterochromatin is clumped chromatin that can block transcription by making the DNA physically unavailable for transcription. Barr body is an inactivated X chromosome in humans and other mammals that is found in females. The binding of proteins can regulate longevity of the mRNA in the cytoplasm. The function and stability of the completed protein can be regulated by chemical modifications. Chapter 15 Differential Gene Expression and Development Development begins with the zygote and continues until death.
Growth occurs through a combination of cell division and cell expansion.
Differentiation produces specialized cells and the overall form of the organism is the result of morphogenesis, due to pattern formation. The fate of cells will be determined at different points during development of embryos of different species. In some species, determination occurs relatively early in cleavage, in other, later. Once determination has occurred, the fate of a tissue and its cells are sealed. Determination precedes differentiation.