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1、Ascomycetes (子囊菌) Ascomycetes are fungi that form their meiotic progeny in a asci (ascus,子囊). This allows the products of meiosis (called a tetrad，四分子) to be recovered together. Some ascomycetes have order asci.Unordered TetradUnordered TetradOrdered TetradOrdered Tetrad粗糙链孢霉粗糙链孢霉酿酒酵母酿酒酵母Our old fri
2、end, Neurospora Neurospora is a haploid Neurospora is a haploid organism that makes asci organism that makes asci with 8 spores.with 8 spores.Neurospora Life cycle粗糙链孢霉粗糙链孢霉同时的同时的 教材教材p70一种能产生分生孢子的特殊真菌菌丝植物生长的 Tetrad Analysis四分子分析Analysis of all four products of a single meiosis.N. crassa spores are
3、formed by a single mitotic division after the completion of meiosis.The meiotic progeny of N. crassa form in a asci (ascus), but they are present in a linear order that reflects meiotic division.Ordered tetrads in Neurospora allow mapping relative to the centromere.Producing an Ordered Tetrad性细胞性细胞
4、Neurospora MeiosisThis shows the process of meiosis in N. crassa.Remember that the duplicated chromosomes that are held together by the centromere segregate during the first meiotic division.Thus, a locus that is close to the centromere would often segregate during the first meiotic division.MI Segr
5、egation PatternA first-division segregation pattern, MINo crossover between gene and centromereMII Segregation PatternCrossover between gene and centromereA second-division segregationPattern, M2Recombination between the gene of interest and the centromere would produce second division segregation t
6、etrads.Producing MII Segregation Patterns教材p180 的4种交换型Tetrads produced by second division segregation are related to the distance from the centromere by this equation:R = (1/2 second-divison / total ) x 100% = cMOrdered Tetrads in Neurospora Allow Mapping Relative to the Centromere MII/total x 100%
7、= cMOrGenetic Analyses with Tetradsa ba ba+ b+ a+ b+ X XCross two haploid cellsCross two haploid cellsa ba ba+ b+a+ b+Induce diploid to undergo meiosisInduce diploid to undergo meiosisGenetic Analyses with Tetradsa ba ba+ b+a+ b+a ba ba+ b+a+ b+ParentalsParentalsa ba ba+ b+a+ b+XRecombinantsRecombin
8、antsa b+a b+ a+ b a+ bProducing MII Segregation PatternsThe distance in cM between a and b can be estimated.Parental Ditype (PD)Tetratype (TT)Nonparental Ditype (NPD)这没有完全概括教材的这没有完全概括教材的P185P185，请补充完好，请补充完好Calculating Genetic Distances with Tetrad AnalysisOrdered(Linear)ExampleNeurosporaGene-GeneDis
9、tanceRF= 1/2T + NPD totalGene-CentromereDistance MII/totalPage 184 (教材上册)ababa+b+a+b+ab+ab+a+ba+babab+a+b+a+baba+ba+b+ab+aba+b+a+b+abab+a+ba+bab+ab+a+ba+b+ab711181801TypeFor aFor bPage 184 (教材上册)ababa+b+a+b+ab+ab+a+ba+babab+a+b+a+baba+ba+b+ab+aba+b+a+b+abab+a+ba+bab+ab+a+ba+b+ab711181801TypeFor aFor
10、 bNPDNPDMIMIMIMIT TMIMIMIIMIIT TMIIMIIMIMIPDPDMIIMIIMIIMIINPDNPDMIIMIIMIIMIIPDPDMIMIMIMIT TMIIMIIMIIMIIPage 184 (教材上册)Distance from a to centromere =Distance from a to centromere = MII = (1+8+1) = 0.05 = 5 map units MII = (1+8+1) = 0.05 = 5 map unitsTotalTotal 100 100Distance from b to centromere =D
11、istance from b to centromere = MII = (18+8+1) = . = 13.5 map units MII = (18+8+1) = . = 13.5 map unitsTotalTotal 100 100Distance from a to b =Distance from a to b = T + NPD = (18+1+1) +1 = .11 = 11 map units T + NPD = (18+1+1) +1 = .11 = 11 map units Total Total 100 100Page 184 (教材上册)a ab b11 mu11 mub b13.5 mu13.5 mu5 mu5 mua aa ab b5 mu5 mu8.5 mu8.5 muBest solutionBest solution
