Distinct Traits In Pea Plants example essay topic

We have known for centuries that traits are passed from parents to offspring. What has not always been understood is how traits are determined. One explanation that appealed to scientist for many centuries was that traits of parents were blended, or mixed in offspring. The blending hypothesis accounted for many observable traits and was widely accepted for many years.

However, the idea of blending could not account for the appearance of unexpected traits in some offspring. It was not until scientist discovered the cellular basis of life that the inheritance of traits was better understood. The first clues to understanding inheritance came from Gregory Mendel, one of the most outstanding scientists in the field of genetics. Mendel, an Austrian monk, began his work in the 1860's. He used garden pea plants to study how traits were passed from one generation to another. The structure of the pea flower enabled Mendel to isolate an important variable, fertilization.

In fertilization, the male plant gamete, located at the base of the pistil. The relatively closed structure of the pea flower petals makes it very easy for pollen from the anther to fertilize the pistil of the same flower. This process is called self-fertilization. If a plant or any organism receives the same genetic traits from both of its parents, it is called purebred. Self-fertilization produces purebred pea plants. As you can see Mendel also altered plants and transferred pollen by hand.

By controlling pollination and preventing self-fertilization, Mendel crossbred plants, producing hybrids. A hybrid is an organism that receives different forms of a genetic trait from each parent. Garden pea plants have some traits that are easy to see, which made it possible for Mendel to produce observable results. Mendel studied seven traits. Each of these traits is unusual in that it has only two distinct forms.

For example, the pea pods are either yellow or green. There is no intermediate or blended color. The height of the plant is tall or short, never medium. Distinct traits like this are rare in nature, as you will see later in this unit. The distinct traits in pea plants allowed Mendel to see his results without guesswork. Another important feature of pea plants is that most plants reproduce in about 90 days.

The short reproductive cycle gave Mendel results relatively quickly and allowed him to repeat the experiments many times to test his results. What results did Mendel expect? According to the blending hypothesis, the green and yellow, Peas of Mendel's plants in the P generation should have blended to produce chartreuse off-spring. Instead, Mendel found that all of that F hybrid plants had yellow peas. There were neither green nor chartreuse peas in the first generation of pea plants, even though one of the parent plants had green peas. When Mendel let the F hybrid plants self-fertilize, he found out that things are not what they always seem and even if they are then you will need to see me and see me good.