MOL - Development [LESSON]

Development

During development, a human or other multicellular organism goes through an amazing transformation. Over the course of hours, days, or months, the organism turns from a single cell called the zygote (the product of sperm meeting egg) into a huge, organized collection of cells, tissues, and organs. As an embryo develops, its cells divide, grow, and migrate in specific patterns to make a more and more elaborate body. To function correctly, that body needs well-defined axes (such as head vs. tail). It also needs a specific collection of many-celled organs and other structures, positioned in the right spots along the axes and connected up with one another in the right ways. The cells of an organism's body must also specialize into many functionally different types as development goes on. Your body contains a wide array of different cell types, from neurons to liver cells to blood cells. Each one of these cell types is found only in certain parts of the body—in certain tissues of certain organs—where its function is needed. How does the coordination of early development work to ensure that only certain genes are expressed in certain cell types?

Watch the following video to learn more about this amazing Development process.

Stem Cells

Stem cells are undifferentiated biological cells found in multicellular organisms, that can differentiate into specialized cells (asymmetric division) or can divide to produce more stem cells (symmetric division). In mammals, there are two broad types of stem cells: embryonic stem cells, which are isolated from the inner cell mass of blastocysts, and adult stem cells, which are found in various tissues.

Pluripotent, embryonic stem cells originate as inner cell mass cells within a blastocyst. These stem cells can become any tissue in the body, excluding a placenta. Only cells from an earlier stage of the embryo are totipotent, able to become all tissues in the body and the extraembryonic placenta.

Cytoplasmic Determinants

Cytoplasmic determinants are molecules passed to the egg from the ovary. These molecules help developing cells to detect relative position. 

One of the best examples is bicoid, which distributes in a concentration gradient to organize the anterior and posterior axes of Drosophila (fruit fly).  When bicoid is placed on both ends of the developing embryo, the organism has two anterior (head) regions. When bicoid is not present, the organism has two posterior regions.

Cell to Cell Communication

Extrinsic (positional) information is received from the cell's surroundings. For instance, a cell might get chemical signals from a neighbor, instructing it to become a particular kind of photoreceptor (light-detecting neuron).

Cells use these mechanisms and many others to grow and develop into the large, complex, multicellular organisms that make up the eukaryotic kingdom.

Take a look at the Homeotic Presentation below.

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