steve is a cheater - Chapter 4b Specialized eukaryotic...

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Chapter 4b Specialized eukaryotic mapping techniques. A tetrad represents the products of a single meiosis that remain together. Example: Yeasts, some algae, basidiospores ( Basidiomycetes), asco spores (Ascomycota). Ascomycota spores are in a sac called the ascus. Haploids are convenient to work with. Small size. Dominance does not hide recessive alleles. Tetrad analysis allows us to study the result of an individual meiosis. If Aa produces 50% (a) and 50% (a) we assume that this is a result of equal segregation for each meiosis. However, without examining individual meioses we cannot confirm this. Examination of individual meioses in ordered asci also allows the mapping of loci with respect to the centromere. For some loci human sperm (haploid) can be evaluated for recombination. See page 180. Linear tetrads can be used to map loci with respect to the centromere and to map loci with respect to each other. Unordered tetrads can be used to map loci with respect to each other.
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Linear tetrads are produced as a result of the spindle arrangement for each of the divisions. The spindles of the of the first and second meiotic divisions and of the postmeiotic mitosis in the case of an octad are positioned end to end in the ascus. Students should be able to draw the diagrams for a MI and a MII meiosis. Page 182, Figs. 6-7 and 6-8. The mII proportion reaches a theoretical maximum at 67% and therefore, the
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steve is a cheater - Chapter 4b Specialized eukaryotic...

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