BIOL 039 Lecture Notes - Lecture 24: Transposable Element, Moe Williams, Chromosome
Document Summary
Mcclintock discovered transposition using crosses involving three linked genes located on the 9th chromo-some. C = purple kernels, c1 = colorless; Sh = plump kernels, sh = shrunken; Wx = shiny kernels, wx = waxy. In crosses with one strain of maize, mcclintock observed an unusual phenomenon: In a trihybrid c,sh,wx/c1,sh,wx, offspring she found kernels that were mostly purple but had sectors that lacked color in various patterns; the colorless sectors were all shrunken and waxy. The strain with unusual kernel coloration also displayed frequent breaks in chromosome 9. Mcclintock observed that the break points of chromosome 9 all occurred in the same position of the affected chromosome. The site of the break she called a dissociation (ds) element. A detailed analysis showed that it is the nuclei of cells from the colorless sectors had a terminal deletion of one chromosome 9 homolog. The chromosome 9 homologs in the purple sectors were both intact.
