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Inheritance160-page5 - The Chromosome Theory of Inheritance...

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Inheritance Patterns - 5 We observed this independent assortment during meiosis when the homologous pairs of chromosomes align along the equator at metaphase I. Maternal chromosomes of some pairs align towards one pole some of the time, and the other pole some of the time. Each meiosis event has a different alignment pattern. Equal numbers of each of the four possible phenotypes result with a dihybrid test cross, which crosses an individual heterozygous for both traits with one that is homozygous recessive for both traits. Dihybrid Test Cross Beyond Mendel Mendel's research occurred before we had knowledge about chromosomes, molecular genetics, mitosis or meiosis. All of Mendel's genes had dominant and recessive forms, and each of his characteristics was found on different chromosomes. Early on, some inheritance patterns did not match the expectations proposed by Mendel's principles. We shall now turn our attention to some gene actions that go beyond the basic Mendelian predictions.
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Unformatted text preview: The Chromosome Theory of Inheritance Gregor Mendel's work was "rediscovered" in 1900 by three independent geneticists who had done studies that came to the same conclusions that Mendel had made. They had the advantage that the processes of mitosis and meiosis were known explaining how genes could be separated. The next step was accomplished in 1902, when Sutton and Boveri correlated Mendel's conclusions about genes (or inherited traits) to the behavior of chromosomes during mitosis and meiosis. Sutton is credited with first proposing the chromosome theory of inheritance: • Chromosomes are in pairs • Homologous Chromosomes separate during meiosis so that alleles are segregated • Meiotic products have one of each homologous chromosome but not both • Fertilization restores the pairs of chromosomes And -- Genes are located on chromosomes....
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