He assumed some type of inherited factor produces white flowers and some other inherited factor produces violet flowers. Did the white-flower factor just disappear in the F1 generation? If so, then the offspring of the F1 generation — called the F2 generation — should all have violet flowers like their parents. To test this prediction, Mendel allowed the F1 generation plants to self-pollinate. He was surprised by the results. Some of the F2 generation plants had white flowers.
He studied hundreds of F2 generation plants, and for every three violet-flowered plants, there was an average of one white-flowered plant. Mendel did the same experiment for all seven characteristics. In each case, one value of the characteristic disappeared in the F1 plants and then showed up again in the F2 plants. And in each case, 75 percent of F2 plants had one value of the characteristic and 25 percent had the other value.
Based on these observations, Mendel formulated his first law of inheritance. This law is called the law of segregation. It states that there are two factors controlling a given characteristic, one of which dominates the other, and these factors separate and go to different gametes when a parent reproduces.
Mendel wondered whether different characteristics are inherited together. For example, are purple flowers and tall stems always inherited together? Or do these two characteristics show up in different combinations in offspring? To answer these questions, Mendel next investigated two characteristics at a time. For example, he crossed plants with yellow round seeds and plants with green wrinkled seeds. In this set of experiments, Mendel observed that plants in the F1 generation were all alike.
All of them had yellow round seeds like one of the two parents. When the F1 generation plants were self-pollinated, however, their offspring—the F2 generation—showed all possible combinations of the two characteristics.
Some had green round seeds, for example, and some had yellow wrinkled seeds. These combinations of characteristics were not present in the F1 or P generations. Mendel repeated this experiment with other combinations of characteristics, such as flower color and stem length.
Each time, the results were the same as those shown in the figure above. The results of Mendel's second set of experiments led to his second law. This is the law of independent assortment. It states that factors controlling different characteristics are inherited independently of each other. You might think that Mendel's discoveries would have made a big impact on science as soon as he made them, but you would be wrong.
Because Mendel's work was largely ignored. The female part of the pea plant is called the pistil, which contains the style, the stigma and the ovary. In order for the pea plant to reproduce, the pistil must be fertilized by the pollen grains. Self-pollination occurs when the flowers are closed and pollen from the plant falls on the female ovary of the same plant, and this happens before the flowers open. This adaptation also reduces the chance of genetic variability. Peas, as well as beans, peanuts, tomatoes, eggplant, peppers and lettuce are mainly self-pollinating.
When the pollinator moves to the next flower, these grains are transferred to the pistil and the flower is fertilized. Some plants are also cross-pollinated by wind, which picks up the grains and disperses them into the open flowers. Because the allele that produces wrinkled peas is recessive, the offspring of this cross will all have wrinkled peas. I noticed that sometimes offspring seem to have traits that their parents did not show.
I called the traits that appeared to mask or hide other traits dominant. I called traits that seemed to be hidden recessive. In this section of the web lab, students experiment with pea plants to try to discover which alleles are dominant and which are recessive. Using four different pea plants, students can cross plants with themselves or with each other to determine dominance.
Which color is dominant, white or purple? This is a pedigree. You can cross plants with themselves or with each other. When a student clicks on one of the plant symbols a white or a black box , the cross button appears. If the student selects two plants, then the two plants are crossed and the offspring appear below. If a student selects only one plant and clicks the Cross button, then the plant self-fertilizes and the offspring appear below.
Students can cross plants as many times as they want before deciding which allele is dominant. Students can explore all seven of the pea traits that Mendel explored in this section. Pea flowers contain both male and female parts, called stamen and stigma , and usually self-pollinate. Self-pollination happens before the flowers open, so progeny are produced from a single plant.
Peas can also be cross-pollinated by hand, simply by opening the flower buds to remove their pollen-producing stamen and prevent self-pollination and dusting pollen from one plant onto the stigma of another. Mendel followed the inheritance of 7 traits in pea plants, and each trait had 2 forms.
He identified pure-breeding pea plants that consistently showed 1 form of a trait after generations of self-pollination. Mendel then crossed these pure-breeding lines of plants and recorded the traits of the hybrid progeny. He found that all of the first-generation F1 hybrids looked like 1 of the parent plants.
For example, all the progeny of a purple and white flower cross were purple not pink, as blending would have predicted. However, when he allowed the hybrid plants to self-pollinate, the hidden traits would reappear in the second-generation F2 hybrid plants.
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