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Unformatted text preview: 7.06 Spring 2004 PS 7 1 of 7 Problem set 7 1. You are a brilliant yeast biologist that has developed a method with which to follow the segregation of chromosomes during meiosis. In your system, chromosomes can be visualized by “marking” them with a GFP fluorescenct signal (a Tet-operator DNA sequence has been integrated into a single chromosome and a Tet-Repressor (Tet- operator binding protein) fused to GFP binds to this DNA element, thereby producing a single fluorescent dot on the Tet-operator containing chromosome). In your diploid yeast strain one homologue of chromosome 5 has the Tet-operator while the other homologue does not. This will allow you to follow the fate of a single homologue during meiosis. During pre-meiotic S phase each homologue is replicated. However, because each pair of two sisters is tightly associated you cannot resolve the two Tet-Repressor-GFP dots on each sister of the “marked” chromsome 5(remember the other homologue (two sisters) are not marked). Therefore, in metaphase 1, you can see only a single GFP dot in the nucleus, corresponding to the paired sisters of one homologue of chromosome 5. After the reductional division of anaphase I, two nuclei are produced, only one of which has the GFP dot. However, after anaphase II, the two sisters are separated and now you can resolve two dots. Therefore, after anaphase II, four spores are produced, two of which have GFP dots because they received a chromatid corresponding to the marked chromosome 5 while the other two spores received a chromatid from the unmarked chromosome 5. S phase Ana I Ana II 7.06 Spring 2004 PS 7 2 of 7 a) In a spo11 null mutant, DSB are never made and so the homologues never pair. Co-orientation of kinetochores is unaffected, however. Draw what you predict the Anaphase I and the Anaphase II two cells would look like in this mutant. b) Would a spo11 mutant have increased rates of chromosome mis-segregation? Why or why not? c) MAMI is a gene that is essential for the co-orientation of sister kinetochores because in its absence sisters are bi-oriented at Metaphase I. These cells cannot initiate anaphase I. Provide an explanation....
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This note was uploaded on 01/23/2012 for the course LSM lsm1301 taught by Professor Seow during the Spring '11 term at National University of Singapore.
- Spring '11