BSCI222 – Lecture 17 (11/5/13) (after Test 2)- Genetic Mapping- Based on recombination rate, which correlates with distance in bp between genes but not perfectly. o Recombination happens in Meiosis I- A lot of the detailed work on recombination was done on common bread mold (neurospora), because the products of Meiosis (spores) get held together in a sac (called ascus), and it’s a haploid. Diploid from 2 made by fusion -> immediate Meiosis I, then II (4 products), then mitotic doubling (8 sets of chromosomes, distributed each to a spore).o Study diagram of meiosis and mitosis forming the ascus (+’s and –‘s).o Which end of the chromosome does the phenotype correspond to? The segregation that happened in Meiosis II (the pattern of white and black on the + and – diagram tells you where the segregations happened). Different strains have different spore colors; looking at the patterns tell you which chromatids exchanged arms. - At Meiosis I, as part of the pairing of the homologues in the synaptonemal complex, thereis typically at least one chiasma (cross-over) per chromosome arm (varies between species and even with size of chromosome, but at least one in a typical vertebrate, kind ofa requirement for progression through meiosis). The probability of a chiasma at any interval on a chromosome is roughly proportional to the inverse of the distance (really close together, less likely to recombine). Recombination is essentially random.- Rest of notes on cheat sheet handout for trihybrid
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