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Unit 8: The Genetic Consequences of Meiosis

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    • 8.1: Mendel's Monohybrid Crosses
      Gregor Mendel (1822-1884) was an Austrian monk who discovered the basic rules of inheritance. From 1858 to 1866, he bred garden peas in his monastery garden and analyzed the offspring of these matings. The garden pea was good choice of experimental organism because many varieties were available that bred true for clear-cut, qualitative traits.
    • 8.2: Crossing Over and Genetic Recombination in Meiosis
    • 8.3: The Evidence of Creighton and McClintock
      In 1932, the geneticists Harriet Creighton and Barbara McClintock provided an elegant demonstration that the recombination of genes linked on a chromosome requires the physical exchange of segments of the chromosome with its homologous partner. During their studies of linkage in corn, they developed a strain of corn that had one chromosome (number 9 of 10 pairs) with two unusual features: (1) a knob at one end of the chromosome and (2) an extra piece at the other.
    • 8.4: Genetic linkage and Genetic Maps
    • 8.5: Gene Mapping with Three-point Crosses
      The closer the intervals examined, the more accurate the map. A three-point cross also gives the gene order immediately.
    • 8.6: Quantitative Trait Loci
      The rules of inheritance discovered by Mendel depended on his wisely choosing traits that varied in a clear-cut, easily distinguishable, qualitative way. But humans are not either tall or short nor are they either heavy or light. Many traits differ in a continuous, quantitative way throughout a population. This can be explained by assuming it is controlled by several pairs of genes — called quantitative trait loci (QTL) — the effects of which are added together (called polygenic inheritance).
    • 8.7: Mapping the Genes of T2
    • 8.8: rII Locus of T4

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