HMB265H1 Lecture Notes - Lecture 8: Endosperm, Synapse, Gene Conversion
19 Oct 2016
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Recombination - morgan, mcclintock, creighton: crossing-over and chiasmata, recombination mechanism by holliday. Expected a 9:3:3:1 phenotypic ratio, but instead observed a different ratio. Certain combinations came up more frequently than others. Also found a skewed phenotypic ratio also via a test cross. Need only observe the female because you know genotype of male. Can only be made from a recombinant gamete and a tester gamete from f1. Morgan"s first prediction: the two genes tested were located on the same chromosome. Two genes (alleles) located on same chromosome do not sort independently. This results in recombinant that appears less than 50% of the time. Genes must be on separate chromosomes to sort independently. Chiasmata - regions where nonsister chromatids of homologous chromosomes cross over each other. Physical exchanges among nonsister chromatids - visualized as chiasma: several crossing-over events occur within each bivalent or tetrad in each meiosis. Chiasmata physically hold homologues together and assure proper segregation in.
