Cell differentiation occurs when cells become specialized in structure and function. Morphogenesis is the process that gives organisms their shape. In animals, cells and tissues must move in order to transform an early embryo into its three-dimensional organism. In plants, morphogenesis and growth are not limited to embryonic and juvenile development like in animals. Plants never stop growing because of apical meristems, which are perpetually embryonic regions in the plant's shoots and roots. (Campbell) (Brose)

Clones are any reproduction of an organism or part of an organism using the DNA of another. In 1997 Dolly was the first sheep to be successfully cloned. This proved that the nucleus of another animal could be produced to fully differentiate all necessary cells. However, certain problems have arisen when cloning animals. Almost all of the cloned animals have sufferend from defects, especially premature death. This may be occuring because the original DNA comes from a specialized cell, which has to turn on its repressed genes, meaning getting rid of its extra functional groups. Therefore, reprogramming of donor nuclei is not always as complete as hoped for. (Campbell) (Brose)

Totipotency

            Any cell that is capable of dedifferentiating its cells and then differentiating them again is said to be totipotent. This term was coined in the 1950s when F.C. Steward conducted cloning experiments on carrots at Cornell University. Steward and his students took cells from a carrot and placed them in a culture medium. Over time, they found that the cells despecialized and then reproduced more unspecified cells. After producing enough unspecialized cells, the cells differentiated again and produced carrots identical to the parent carrot. (Hartsock)

     In Animals

          in  animals differentiated cells generally don't dived in a culture, so researchers had to figure out a different way to find out if differentiated animal cells can be totipotent. They removed the nucleus of an unfertilized egg cell or zygote and replace it with the nucleus of a differentiated cell, this is called nuclear transplantation. The nucleus, depending on its retaining its genetic capability,  should be able to direct development of the recipient egg into all the proper tissues and organs of an organism.  (Davis)

Pattern formation is the growth and development of tissues and organs in certain areas of an organism so that it develops into a complete and normal organism. Pattern formation begins during the early stages of life and can continue all the way though life depending on the type of organism. (Ryan)

Campbell, Neil A., and Reece, Jane B. AP Edition Biology. 7th. San Francisco: Pearson Benjamin Cummings, 2005.

Stem Cells

a stem cell is an unspecialized cell that can reproduce itself indfinitely and differentiate into specialized cells of one or more types. Stem cells can be found in early animal embryos athe the blastula stage and from the adult body. tTe cells from the blastula stage can produce indefinitely and can differentiate into various specialized cells. THe ones from an adult body are to replace nonreproducing specialized cells as needed, they are pluripotent, or they can produce multiple but not all cel types. THe main goal for stem cell research is to be able to repair damaged or diseased organs. (Davis)

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Programmed Cell Death (Apoptosis)

Another outcome of cell signaling that is crucial in animal development is programmed cell death, or apoptosis. Apoptosis, by definition, is the changes that occur within a cell as it undergoes programmed cell death, which is brought about by signals that trigger the activation of a cascade of suicide proteins in the cell destined to die. A cell shrinks and becomes lobed (called "blebbing"), the nucleus condenses, and the DNA is fragmented during apoptosis. Surrounding cells engulf and digest the membrane-bound remains. Ced-3 and Ced-4 encode proteins essential for apoptosis. When a death signal is received by the cell, the apoptosis pathway activates proteases and nucleases, enzymes that cut up the proteins and DNA of the cell. The pathway used that leads to apoptosis depends on the type of cell and on the particular signal that triggers apoptosis. (Mroz)

Plant Development

Cell lineage is much less significant in formation of platns as opposed to animals. Most of these plants are totipotent. The fates of these organisms depend mostly on positional info rather than cell lineage. Inside the seed is where cell division, morphogenesis, and differentation occur. Many environmental signals trigger transduction pathways which translate shoot meristems into floral meristems. This causes a plant to flower. Floral meristem consists of L1-L3. All of these contribute to the formation of the flower. Some issues with new plants are that they are chimeras, or organisms with a mixture of different cells. If a plant has a homeotic mutation, it means organs are missing or repeating. (Brandt)

Chimaeras are organisms made up of a collection of genetically different cells. The best example of these can be found in plants and have genetically identical cells from two separate parents. (Ryan)

Campbell, Neil A., and Reece, Jane B. AP Edition Biology. 7th. San Francisco: Pearson Benjamin Cummings, 2005.

Comparing Plants and Animals

Plants contain rigid walls, which in turn rule out the process of morphogenetic movements of cells. Morphogenetics in plants relies on selective cell enlargement. However. despite the differences between plants and animals, one thing is common, the origin of cells. Both developments rely on transcriptional regulating of genes. However, the genes that conduct these processes differ between the two. (Brandt)

Campbell, Neil A., and Reece, Jane B. AP Edition Biology. 7th. San Francisco: Pearson Benjamin Cummings, 2005

Review Questions!

1. Although quite different in structure, plants and animals share some basic similarities in their development, such as...

a. the importance of cell and tissure movements

b. the importance of selective cell enlargement

c. the importance of homeobox-containing homeotic genes

d. the retention of meristematic tissues in the adult

e. master regulatory genes that encode DNA-binding proteins

2. cell differentiation always involves...

a. the production of tissue-specific proteins, such as muscle actin

b. the movement of cells

c. the transcription of the myoD gene

d. the selective loss of certain genes from the genome

e. the cell's sensitivity to environmental cues such as light or heat (Ramey)

answers..e, a

Campbell, Neil A., and Reece, Jane B. AP Edition Biology. 7th. San Francisco: Pearson Benjamin Cummings, 2005

Reproductive Cloning of Mammals (Awan)

- researchers have been able to clone animalsusing nuclei or cells from a variety of early embryos.

-1997, birth of Dolly the Sheep, a lamb clones from an adult sheep by nuclear transplantation from a differentiated cell. Dolly suffered premature derath because hers cells were "older" than those of a normal sheep.

-animal cloning is not perfect. Most of the time, the cloned aninmals suffer from diseases.(Awan)

Campbell Neil A. and Jane B. Reece. AP EDITION BIOLOGY. 7th. San Francisco: Pearson Benjamin Cummins