Quiz 5 You are given two haploid strains of yeast with opposite mating types. Bo

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Quiz 5 You are given two haploid strains of yeast with opposite mating types. Both of these strains grow on minimal medium containing arginine, but not on minimal medium lacking arginine. You generate a diploid strain by mating them. The diploid grows on minimal medium lacking arginine, suggesting that the two strains have recessive mutations in different genes, both of which cause an Arg-growth phenotype. We will designate them arg20 and arg30. You induce diploid cells to undergo meiosis (sporulation) and analyze 100 of the resulting tetrads for ability of the haploid spores to grow in the absence of arginine. You find three different classes of tetrads, in the numbers indicated below. Arg : Arg 4 :0 40 20 40 2: 2 a) Are arg20 and arg30 linked? (yes or no) b) Can you say anything else about the chromosomal locations of these genes, in three sentences or fewer

Explanation / Answer

Tetrads are characteristic structures of the sexual state of some fungy, witch represent an unique oportunity for genitic studies, because they hold the 8 gametes produced trought meiosis from a single cell.

If genes arg20 and arg30 where independently sorted (not linked), it could be expectable to find the same (or nearly the same) porportion of Arg+ or - phenotypes within each tetrad.

As this is not the case, it can be asumed than a) arg20 and arg30 are linked.

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