Mixture Of It All Essay, Research Paper
Introduction
I did my research on plant reproduction/breeding. What is PLANT
REPRODUCTION/BREEEDING? How DO PLANTS REPRODUCE? This
information will be included in my report. I will tell you how many ways
plants can reproduce. And I will give an example of each way of
reproduction there is.
Plant Reproduction
Plant Reproduction is to make off springs. Plants reproduce two ways
sexually and asexually. Sexually means there are two sources and asexually
means there is one source. Asexual plants reproduce by themselves. And
sexual plants reproduce with another plant or source. A flower has 4 parts.
Sepals surround and protect the other parts of a developing flower before it
opens. Petals make up the next whorl most animal pollinated flowers have
brightly colored petals.
The two innermost whorls of flower parts contain the reproductive
structures. The male reproductive structures are stamens, each which consist
of an anther and a filament. An anther contains microsporangia, which
produce micrspores that develop into pollen grains. A stalklike filament
supports an anther . The innermost whorl contains the female reproductive
structures, which are called carpels. One or more carpels fused together
make up the structure called a pistil. The enlarged base of a pistil is called
the ovary. A style, which is usually stalklike, rises from the ovary. The tip of
the style is called the stigma. Usually a stigma is sticky or has hairs,
enabling it to trap pollen grains. Most species of flowering plants have
flowers with both stamens and pistils. However, some species have flowers
with only stamens (male flowers) or pistils (female flowers).
Selection
Individuals within a species vary widely in a number of
characteristics. Many of these traits are heritable and can be passed on their
progeny. In practicing selection, plant breeders choose plants with desirable
traits for further propagation and discard plants that are inferior for that trait.
By doing so, plant breeders can select and reselect for the
trait through successive generations, shifting the population in the desired
direction.
Hybridization
Hybridization involves crossing plants of different strains or types to
join in the progeny the desireable traits of both parents. Undesirable traits
also enter the combination, however, so hybridization is usually followed by
several generations of selection. This allows breeders to discard undesirable
plants, choosing for further propagation only those plants with the desired
combination of traits.
Backcrossing is a common variation of hybridization. This technique
is often used to transfer into a desirable variety a beneficial trait from an
otherwise undesirable parent. First the hybrid between the two parents is
made, then the hybrid is crossed with the desi
this backcrossing normally segregate widely, with individual plants showing
a mixture of the characteristics of both parents. By continued backcrossing
and selection the plant breeder concentrates the qualities desired, and, if all
goes well, in six or seven generations the variety once again breeds true but
now exhibits its new trait. Backcrossing is valuable for adding single gene
characteristics to crop plants, particularly for resistance to specific insects
and diseases.
When desirable charcteristics are fully developed in a hybrid plant,
and the plant can be propagated asexually by budding, grafting, or cloning,
then no further selection is necessary. A hybrid apple, for example, is
propagated by grafting, so all resultant plants are identical.
Hybrids are often more vigorous than either parent. This phenomenon
is called hybrid vigor and has been widely used by plant breeders to increase
crop yielders. Hybrid seeds have helped to double U.S. corn yields since the
1940s, and almost all the corn now grown in the United States and Europe is
started annually from hybrid seed. Hybrid breeding has expanded in recent
years, and hybrid varieties are now common in grain crops, vegetables, and
many flower species.
Mutation
Occasionally an individual plant shows an important change in one or
more traits arising from a spontaneous mutatation. Usually a change in a
single gene is involved. Most mutations are deleterious, bt occasionally one
has a distinct advantage. The plant showing the mutation may be used
directly as a variety, a common practice in apples and other fruits, or the
new trait may be added to exisiting varieties through hybridization and
backcrossing. Plant mutations caused by single-gene changes have found
wide use in ornamentals, resulting in double-flowered forms, weeping stems,
dwarfism or unusual. Mutations can be induced artifically by X rays or
ultraviolet light.
Doubling the number of chromosomes is another plant-breeding
technique that has been useful in improving some flower and crop plants,
sometimes producing forms with increased vigor and with larger leaves,
flowers, and fruits.
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