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13. Briefly explain role of DNA, genes and chromosomes in heredity. Describe genetic variability and its role in nature, especially in terms of biodiversity. Define a hybrid.
I. DNA.
DNA is the chemical Deoxyribo Nucleic Acid, which makes up the genetic code. It is found in every cell's nucleus. It is precisely duplicated before a cell divides and then equally distributed to each resulting daughter cell.DNA provides ALL the genetic information of the cell and organism in which it is found.
II. GENES.
Genes are the functional units of DNA, strung together in chromosomes. (See figure 13) Genes generally control a single trait of the plant, like, like color.
III. SEXUAL REPRODUCTION.
When produced by sexual reproduction, no plant (or animal) will be genetically identical and, therefore, the resulting offspring will have genetic variably.A. Genetic variability (basically differences in DNA content) of organisms will be different: some having more and diferent variations from others. This can be important in survival.
We usually can see the genetic variability most clearly among humans. Look at any group of people and see how none look the same. This is true of any group of plants but we are less able to see it.
B. An example of the survival role of genetic variability in the potato.
Crop plants may be almost genetically identical, like the Idaho potato. They are selected and developed that way by agricultural scientists. As a result, they all grow and produce in similar and desirable ways.
However, if a new potato disease is introduced, they all may succumb to it. This happened in Ireland during the 1830's Potato Famine. Thousands of people died of starvation in Ireland and many immigrated to the United States.
C. Biodiversity is the collective genetic diversity of life: all known and unknown species in existence.
1. It is desirable to maintain biodiversity in wild plants and animals, as well as in cultivated ones. This provides a "genetic bank" which preserves genetic variability.2. If a new condition or environmental change develops, there is some possibility that genes are present in the different genetic types which could offer protection or better adaptation to the new situation.
(Note: The genetic resource is present BEFORE the change. It does not develop as a result or a response to an environmental shift - a very common misconception about how genetic changes.)
3. We presently know that biodiversity is being lost rapidly throughout the world through environment changes, many due to human activities. Some estimate that the world's extinction rate is 100 to 1,000 times greater now than in the past.
The "genetic banks," that is, the total genetic makeup found in the many different types of life forms, are being lost. They are the products of millions of years of evolution. There is no way to recapture them. We may have no idea of what we have lost.IV. HYBRIDS.
A Hybrid is the product of crossing (mating) different varieties of plants (or animals).Hybrids can occur naturally in the wild or be a product of a careful work by geneticists.
Hybridization can refer to a cross between two plants that have only one major genetic difference, or, more dramatically, between species of different genera, as found in the Hawaiian silverswords. (see L.O. #26 for more details on natural hybrids among silverswords.)
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