Mendel's Investigations of the Pea Plant – Classic Mendelian Genetics

by Georgina Cornwall, PhD

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    00:01 Gregor Mendel came along and the key for him was his background in mathematics. Mendel was a very well-schooled man and he could put together his understanding of science with his understanding of mathematics and makes some predictions about what might have been going on and this is where he came up with the concept that there were two alleles for the same character perhaps or maybe even more. But he was examining two alleles and that is where we will explore for this time.

    00:32 Why is that that Mendel chose to work with pea plants? First of all, there are many variations of pea plants, many variations within pea plants. In addition, there had already been previous work in which plants had been hybridized. They are easy to grow and they don't take a lot of time to grow. In addition, they were capable of self-fertilizing and with some modifications, cross fertilizing. Mendel had ultimate control of his model of study.

    01:06 Let us take a look to start with at the pea plant and how self-fertilization might happen versus cross-fertilization. First of all, it is key to understand that the pea plant has both male and female components in its flower. So it has anthers, which contain pollen under the male as well as carpels, which contain the female ovule. Now self-fertilization would be the normal case. So you could easily self-fertilize by pollen coming from the anthers and brushing straight on to the carpels of that same flower. Mendel though wanted to be able to cross fertilize that as well as self fertilize and in this case, he would take pollen from one true breeding plant and apply it another true breeding plant. Because he was able to remove the anthers, he could stop self fertilization. He would take the pollens say here from the white plant and paint it on the carpels of the purple plant who had had its anthers removed and he would look at the progeny. In this case, they all came out looking like the purple flowers.

    02:22 Mendel could also perform reciprocal crosses. Reciprocal simply means doing it the other way round in which case he would be taking pollen from a purple flower and applying it to a white flower who had had its anthers removed and he noticed we have the same outcomes.

    02:41 So he chose seven true breeding traits that exhibited segregation. There is a little controversy as to why he didn't he chose other traits, but the other here is that he chose seven traits that showed this pattern where the one phenotype or the appearance disappeared and then reappeared in the next generation. The seven phenotypes that he chose were seed shape either round or wrinkled. We had seed color yellow or green. And flower color purple or white. Pod shape. We also can look at pod color and whether a plant is tall or short and then the flower position on the plant. These are traits that he noticed this very same pattern happening with. In the parental generation or the P generation, he would take true breeding parents one that is true breeding purple and one that is true breeding white and by true breeding, we mean pure breeding. He would cross them and cross them and cross them and make sure they were only purple and make sure they were only white. That is what true breeding meant. He would cross those and what we call the F1 cross and become an F1 generation. Cross-fertilization happens and all of the F1 generation look just like one of the parents and when we self-fertilized the offspring from the F1 generation, they will produce phenotypes or appearances where the parent phenotype that went missing shows up again. And so whether he was dealing with round or wrinkled seed or yellow or green seeds, the same pattern of inheritance was exhibited and that is why he chose those traits.

    About the Lecture

    The lecture Mendel's Investigations of the Pea Plant – Classic Mendelian Genetics by Georgina Cornwall, PhD is from the course Understanding Genetics.

    Included Quiz Questions

    1. Number of seeds in a pod
    2. Seed shape
    3. Plant height
    4. Pod color
    5. Flower position
    1. It will always produce offspring with the same traits.
    2. It will always produce offspring with different traits than the parental generation.
    3. It will occasionally produce identical offspring with different traits.
    4. It will always produce slightly different offspring with the almost same phenotypes.
    5. It will always produce phenotypically different offspring with slight genetic variations.

    Author of lecture Mendel's Investigations of the Pea Plant – Classic Mendelian Genetics

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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