04BIS10110152013RecombinLect4

Chiasma

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Unformatted text preview: nd Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 14 Crossing over of non-sister chromatids BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 15 Crossing Over involves Chiasma Crossing ­ Crossing over occurs at the Crossing “4 strand” stage of prophase I of meiosis and involves structures called “chiasma.” “chiasma.” BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 16 Synaptonemal Complex BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 17 Localization of meiotic cohesins during meiotic divisions. Lee J et al. J Cell Sci 2003;116:2781-2790 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2003 by The Company of Biologists Ltd Molecular Basis of Meiotic Recombination:Mov BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 19 Morgan’s 2-factor cross: 4, not 2 class of phenotypes* ­ For two linked genes, a 1:1 phenotypic ratio is expected from a testcross For (homozygous recessive male) with F1 progeny. However, as shown in the (homozygous table below, about 20% of the testcross progeny show recombinant table phenotypes in addition to the parental phenotypes. The recombinant phenotypes progeny produced from the test cross exhibited only one of the two mutant phenotypes. In other words, the + + linkage was broken to yield mutant the + vg (vestigial) and the pr + phenotypes (Table 1). TYPE OF DROSOPHIILA TYPE OF DROSOPH LA GENE COMBIINATIION GENE COMB NAT ON NUMBER OF FLIIES NUMBER OF FL ES WIILD--TYPE W LD TYPE ++//prrvg ++ p v g 2876 2876 PURPLE VESTIIGIIAL PURPLE VEST G AL prrvg//prrvg p vg p vg 2433...
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