BACKGROUND:
Most genes in a uniform population tend to be similar, however
there always seems to be a rare individual that differs from his neighbors.
The cause of this different individual in a natural population is due to a
change in one of the unit genes and is called a mutation.
Some mutations may be economically desirable or advantageous
to individuals, but most mutations result in phenotypes less adapted for
survival than the parent phenotype. Natural mutations are random. Radiation
from some sources like alpha and beta particles, gamma rays, mustard gas, and
x-rays are known to cause mutations but the exact reasons are very
complicated. Some mutations in plants are desirable commercially, even through
they may have no survival value to a plant. For instance, seedless grapes are
missing their reproductive seeds. If humans don't vegetatively propagate the
grape plant it will not survive. Other desirable mutations occur in
nectarines, many ornamental flowers, peanuts and other cash crops.
Plant breeders deliberately increase hereditary variation by
hybridization and stimulate mutations by radiation treatments and other
techniques. Breeders will then select the most desirable phenotypes and
genotypes for propagation. In general, the traits that plant breeders are
looking for are: vigorous plant types, high yields, quality, and disease
resistance.
Genetic engineering is a field that works with controlling
"mutations," and genetic combinations resulting in superior or
helpful organisms. Genetic engineering is different from the hybridization
principles that were studied in this lab. Genetic engineers "design"
genetic combinations that will result in specific and directed genetic
combinations. Hybridization relies on random combinations that are driven by
probability. Hybridization is more of a "trial and error" type of
situation. Breeders try to combine different genetic combinations with hopes
of producing a better phenotype and genotype and unlike genetic engineers,
they do not "design" the genetic combinations themselves.
PROCEDURE:
- Collect a few plant identifiers and seeds that state they
are "hybrids." Write down all the "hybrid" plants that
they see. Make sure that students can recognize when a plant is labeled as a
hybrid.
- You may ask students to look around their house or go to a
local nursery or even grocery store, that sells plants and look at the
information about the plant. Have them either bring the identifier into class
or write down the information. You may want students to go to a local plant
nursery as a field trip.
- If students have seeds at home, have them look at the
package it comes in. See if they are hybrids.
They will be amazed that most of the plants on the market are
products of genetic manipulation.
