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Understanding eukaryotic chromosome mapping techniques.

In haploid yeast, a cross between arg- ad- nic+ leu+ and arg+ ad+ nic- leu- produces haploid sexual spores, and 20 of these are isolated at random. The resulting cultures are tested on various media as shown below (in the table below, + means growth, while - means no growth).
(a) What can you say about the linkage arrangement of these genes?
(b) What is the origin of culture 16?

culture Minimal media plus...
arg arg arg
ad ad ad
nic nic nic
leu leu leu
1 + + - -
2 - - + +
3 - + - +
4 + - + -
5 - - + +
6 + + - -
7 + + - -
8 - - + +
9 + - + -
10 - + - +
11 - + - +
12 + - + -
13 + + - -
14 + - + -
15 - + - +
16 + - - -
17 + + - -
18 - - + +
19 + + - -
20 - + - +
(ad = adenine, arg = argenine, nic = nicotinamide, leu = leucine)

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