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 desirable parent. The progeny from

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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