Saccharomyces_A

Yeast mitotic chromosomes are not visible

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Unformatted text preview: and H4. Yeast mitotic chromosomes are not visible microscopically in the same way human chromosomes are visible in karyotype analysis. Pulse-field gel electrophoresis, which separates intact yeast chromosomes using alternating pulses of current, produces molecular “karyotypes” of the yeast genome, such as the one shown in Fig. A.3b. Geneticists use these karyotypes to confirm the number of yeast chromosomes and to observe major alterations in chromosome structure. As Figure A.3b indicates, chromosome I, about 235 kb in length, is the smallest yeast chromosome. Chromosome XII is the largest; its size varies between about 2060 and 3060 kb because of a variable number of tandem ribosomal RNA genes (rDNA)—usually in the range of 100–200 copies—in different strains. Genetic Maps and Recombination Frequencies The classical genetic map of yeast currently shows the locations of over 1000 markers determined by tetrad analysis (see Chapter 3 of the main textbook). The total genetic map length, a function of the frequency of meiotic recomb...
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