Classical Genetic Assumptions – Classic Mendelian Genetics

by Georgina Cornwall, PhD

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    00:01 In this lecture, we will begin our exploration of classical genetics starting with Mendelian inheritance and his principles of segregation and independent assortment. By the end of this lecture, you should be able to describe what was understood prior to Mendel as well as evaluate the outcomes of mono and dihybrid crosses and relate these to the movements of chromosomes during meiosis. Finally, you should be able to differentiate between the concepts of segregation and independent assortment. Classical assumptions of genetics that is those prior to the 20th century led us to an understanding of blending, but this gave this a sort of a paradox to think about. We understood that heredity occurs within species, but thought that it was about direct transmission as in traits were passed directly to offspring from the parents. No meiosis. Then blending was the idea such that the offspring would be a blend of both parents and maintain blending as the generations progressed. And the problem here was if it was blending and we had said purple from red and blue, then surely everything in the future would be purple. So we would always be going to this intermediate form.

    01:29 Yet, we knew that this wasn't true because we would see features reemerged. So something else had to be going on. There were many people before Mendel. Mendel gets a lot of credit, but before his time, there was work by Josef Kolreuter on tobacco plants where he was looking at hybridization and what he noticed was that if he crossed one set of parents, he would end up with a different form looked more like one set of parents and then when he crossed them again, he would see that the grandparent phenotype or the grandparent’s appearance showed up again. So clearly blending was not the case and then we had T.A. Knight little bit later on. He started looking at pea plants and this really was the springboard for Mendel's work because, in his observations of pea plants, he suggested that there were alternative forms of genes. For example, if you know anything about pea plants, we had purple flowers or white flowers. So there were alternate forms or alleles of the same genes.

    About the Lecture

    The lecture Classical Genetic Assumptions – Classic Mendelian Genetics by Georgina Cornwall, PhD is from the course Understanding Genetics.

    Included Quiz Questions

    1. Alternate forms of traits
    2. DNA in the nucleus of eukaryotic cells
    3. DNA in the nucleus of plant cells
    4. Genes on the chromosomes
    5. Centromeres on the chromosomes

    Author of lecture Classical Genetic Assumptions – Classic Mendelian Genetics

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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