Module # 8: Mendelian genetics
Gregor Mendel was born in Austria in the year 1822, as a peasant. His father was a farmer and taught Gregor about animal breeding and plant grafting, which interested Gregor very much. His learning at school impressed his teacher, and she urged his parents to let him get a higher education, which at that time was equal to high school. His parents agreed but they were so poor that they couldn’t help pay for it. He struggled through his school, almost starving because he couldn’t afford to eat.
When he was done with his school he tried to be a teacher, but failed twice. But a man named Andreas Baumgartner pulled some strings for him and he was admitted to the University of Vienna. While he was there he studied under a man named Johann Christian Doppler. Doppler taught him the way to conduct experiments.
For eight years Mendel conducted experiments on breeding. He raised thousands of pea plants and documented the results of breeding and crossbreeding them. At the end of those eight years he published a paper that held a series of four conclusions which are the basis of what we call the Mendelian genetics.
Sadly, Gregory’s work went unnoticed and Gregor had to give up his scientific endeavors because he became involved in a political controversy. He spent the rest of his life fighting against taxation. When he died in 1884, no one knew the significance of his experiments. But by the 1930’s his work was well known throughout the scientific community.
During his eight years of scientific work, Mendel studied pea plants. He observed that some pea plants were tall, some were short, some had flowers that grew along the sides of the plant (axial flowered plants), some plants had flowers that grew on the top of the plant (terminal flowered plants), some had green pea pods, some plants had yellow pods, some yellow peas, some green peas, some smooth peas, and some wrinkled peas.
Mendel noticed that some plants bred so as to produce offspring with the same characteristic. For example, some tall plants would always give rise to other tall plants. If this happens we say the plant had bred true.
True breeding – if an organism has a certain characteristic that is always passed on to its offspring we say that this organism bred true with respect to that characteristic
Mendel noticed that not all plants bred true. With this in mind, Mendel devised a set of experiments. He took a tall plant that always bred true and allowed it to sexually reproduce with a short pea plant that always bred true. No matter how many times he did this the offspring were always tall. Mendel observed that with other definable characteristics the outcome was similar.
When axial flowered plants were bred with terminal flowered plants the offspring were always axial flowered plants. When green pod plants were bred with yellow pod plants the offspring always possessed green pods. Yellow pea plants bred with green pea plants resulted in yellow pea plants. Likewise, smooth pea plants mixed with wrinkled pea plants produced smooth pea plants.
As pea plants can self breed, Mendel tried experiments in self pollinating pea plants. He noticed that when this happened 75% would be the dominant characteristic, but the other 25% would be the opposite characteristic. For example, a tall pea plant bred with itself would result in 75% of the offspring being tall, but the other 25% would be short.
These two sets of experiments led Mendel to develop four principles of genetics:
1. The traits of an organism are determined by packets of information called “factors”.
2. Each organism has not one but two factors that determine its traits.
3. In sexual reproduction each parent contributes only one of its factors to the offspring.
4. In each definable trait, there is a dominant factor. If it exists in an organism, the trait determined by that dominant factor will be expressed.
How do these principles help explain the data that Mendel collected? Well, Mendel assumed that if a plant always breeds true, it must have two factors that are identical. In other words, if a tall pea plant always produces tall offspring it must have two factors that correspond to the trait of being tall. A short plant that always produces short plants must have two factors that correspond to the trait of being short. Since each parent had two of the same factor, they always contribute that factor to the offspring. Thus, the offspring produced when a true breeding tall plant was bred with a true breeding short plant would always have one factor that corresponded to being tall and on factor that corresponded to being short. By further assuming that the factor corresponding to being tall was dominant, each offspring would be tall, because each offspring had that dominant factor.
Gregor Mendel was born in Austria in the year 1822, as a peasant. His father was a farmer and taught Gregor about animal breeding and plant grafting, which interested Gregor very much. His learning at school impressed his teacher, and she urged his parents to let him get a higher education, which at that time was equal to high school. His parents agreed but they were so poor that they couldn’t help pay for it. He struggled through his school, almost starving because he couldn’t afford to eat.
When he was done with his school he tried to be a teacher, but failed twice. But a man named Andreas Baumgartner pulled some strings for him and he was admitted to the University of Vienna. While he was there he studied under a man named Johann Christian Doppler. Doppler taught him the way to conduct experiments.
For eight years Mendel conducted experiments on breeding. He raised thousands of pea plants and documented the results of breeding and crossbreeding them. At the end of those eight years he published a paper that held a series of four conclusions which are the basis of what we call the Mendelian genetics.
Sadly, Gregory’s work went unnoticed and Gregor had to give up his scientific endeavors because he became involved in a political controversy. He spent the rest of his life fighting against taxation. When he died in 1884, no one knew the significance of his experiments. But by the 1930’s his work was well known throughout the scientific community.
During his eight years of scientific work, Mendel studied pea plants. He observed that some pea plants were tall, some were short, some had flowers that grew along the sides of the plant (axial flowered plants), some plants had flowers that grew on the top of the plant (terminal flowered plants), some had green pea pods, some plants had yellow pods, some yellow peas, some green peas, some smooth peas, and some wrinkled peas.
Mendel noticed that some plants bred so as to produce offspring with the same characteristic. For example, some tall plants would always give rise to other tall plants. If this happens we say the plant had bred true.
True breeding – if an organism has a certain characteristic that is always passed on to its offspring we say that this organism bred true with respect to that characteristic
Mendel noticed that not all plants bred true. With this in mind, Mendel devised a set of experiments. He took a tall plant that always bred true and allowed it to sexually reproduce with a short pea plant that always bred true. No matter how many times he did this the offspring were always tall. Mendel observed that with other definable characteristics the outcome was similar.
When axial flowered plants were bred with terminal flowered plants the offspring were always axial flowered plants. When green pod plants were bred with yellow pod plants the offspring always possessed green pods. Yellow pea plants bred with green pea plants resulted in yellow pea plants. Likewise, smooth pea plants mixed with wrinkled pea plants produced smooth pea plants.
As pea plants can self breed, Mendel tried experiments in self pollinating pea plants. He noticed that when this happened 75% would be the dominant characteristic, but the other 25% would be the opposite characteristic. For example, a tall pea plant bred with itself would result in 75% of the offspring being tall, but the other 25% would be short.
These two sets of experiments led Mendel to develop four principles of genetics:
1. The traits of an organism are determined by packets of information called “factors”.
2. Each organism has not one but two factors that determine its traits.
3. In sexual reproduction each parent contributes only one of its factors to the offspring.
4. In each definable trait, there is a dominant factor. If it exists in an organism, the trait determined by that dominant factor will be expressed.
How do these principles help explain the data that Mendel collected? Well, Mendel assumed that if a plant always breeds true, it must have two factors that are identical. In other words, if a tall pea plant always produces tall offspring it must have two factors that correspond to the trait of being tall. A short plant that always produces short plants must have two factors that correspond to the trait of being short. Since each parent had two of the same factor, they always contribute that factor to the offspring. Thus, the offspring produced when a true breeding tall plant was bred with a true breeding short plant would always have one factor that corresponded to being tall and on factor that corresponded to being short. By further assuming that the factor corresponding to being tall was dominant, each offspring would be tall, because each offspring had that dominant factor.
---Animalia
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