From Seed to Seed:
Plant Science for K-8 Educators
 |
 |
 |
 |
|
From Seed to Seed: |
|
|
Clones and cloning The news story about Dolly, the first official sheep clone, brought the word "clone" into general usage, often with doomsday connotations and great hubbub about the ethical implications. What exactly do the words "cloning" and "clone" mean anyway? Cloning is the duplication of an organism by asexual means, involving mitotic, as opposed to meiotic, cell division. The resulting offspring are genetically identical to the parent, and therefore exhibit the parents' characteristics. A population of genetically identical offspring is called a clone; in common usage the term also refers to an individual created by cloning. Why is cloning important? Primarily because asexual propagation, and the resulting production of clones, is a "backup" plan for many plants. Consider, for example, the common violet (Viola spp.). Violet plants produce a number of  showy
flowers. These flowers attract insects that transfer pollen as they travel
from plant to plant in search of nectar. Successful pollination and fertilization
results in the fusion of gametes, so this is a type of sexual reproduction,
and the offspring are genetically unique. However, violets have evolved a backup plan in the event that insects are not around to do the pollinating. The plants also produce smaller flowers set close to the ground. These flowers are self-pollinating-in fact, they never even open. Still, because we have pollination and the union of gametes, this is also a type of sexual reproduction. In this case, the offspring are still unique, but are most likely genetically very similar to the parent. And, finally, to virtually guarantee the creation of new plants, violets also produce creeping stems. These eventually sprout along their length, forming new plants that are genetically very similar to the parent. This is a form of asexual propagation. We can see that although sexual reproduction is critical to maintaining genetic diversity, asexual propagation is a means by which a plant can reproduce many copies of itself without relying on fickle pollinators or the availability of compatible pollen. Although the independence with which asexually propagating plants reproduce seems ideal, there are drawbacks. A population of genetically identical organisms is not a particularly favorable outcome in nature. As we said earlier, genetic diversity is important because it allows plants to adapt to changing environments. In addition, if a pest or disease were to strike a population of genetically identical individuals, it is likely that the entire population would be wiped out. How, exactly, do plants reproduce asexually? To answer this question, we first must consider the parts of the plant that are involved in the process. |
||||
Made possible by a grant from Oracle Corp. Copyright 2001, National Gardening
Association, Inc. For questions regarding this web site, contact Webmaster |
