key concept 19.1 The Four Major Processes of Development Are Determination, Differentiation, Morphogenesis, and Growth

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Development is the process by which a multicellular organism, beginning with a single cell, goes through a series of changes, taking on the successive forms that characterize its life cycle (Figure 19.1). After the egg is fertilized it is called a zygote, and in the earliest stages of development a plant or animal is called an embryo. Sometimes the embryo is contained within a protective structure such as a seed coat, an eggshell, or a uterus. Embryogenesis results in a new organism with a body plan characteristic of its species. Many organisms continue to develop throughout their life cycles, with development ceasing only at death.

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Figure 19.1 From Fertilized Egg to Adult The stages of development from zygote to maturity are shown for an animal and for a plant. The blastula is a hollow sphere of cells; the gastrula has three cell layers.

Activity 19.1 Stages of Development

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  • In the embryo, determination of the fate of a cell occurs before actual cell differentiation.

  • Experimental manipulations indicate that a differentiated cell in a plant or animal has the whole genome of the organism and the potential to form all other cells of that organism.

  • Cloning of plants and animals using differentiated cells or cell nuclei has several potential uses.

  • Pluripotent stem cells can be obtained from animal embryos or formed from differentiated cells in the laboratory.