You are trying to determine the relative order of three genes involved in lactos
ID: 40349 • Letter: Y
Question
You are trying to determine the relative order of three genes involved in lactose metabolism, lacA lacZ and lacY. They all map by conjugation to 11 min on the E.coli chromosome. You do three experiments using trpE (12min) as an outside marker. In each experiment, you use a wild strain of E.coli as the donor, and a strain that is mutant for trpE and two of the lac genes as the recipient. You select for trpE+ recombinants and then score them for the lac phenotypes. The data for each cross is shown in the tables below. For each table show the order of the two lac genes relative to trpE. Finally, indicate the order of all three lac genes relative to trpE.
You are trying to determine the relative order of three genes involved in lactose metabolism, lacA lacZ and lacY. They all map by conjugation to 11 min on the E.coli chromosome. You do three experiments using trpE (12min) as an outside marker. In each experiment, you use a wild strain of E.coli as the donor, and a strain that is mutant for trpE and two of the lac genes as the recipient. You select for trpE+ recombinants and then score them for the lac phenotypes. The data for each cross is shown in the tables below. For each table show the order of the two lac genes relative to trpE. Finally, indicate the order of all three lac genes relative to trpE.Explanation / Answer
Map distance=(# in SCO phenotypes + # in DCO phenotypes x 100)/ (total # progeny)
Distance between lac Y and lac Z = (16 + 0 + 25) x 100 / (59 + 16 + 25)
= 41 x 100 / 100
= 41 m. u
Hence the genes lac Y and lac Z are located 41 map units apart.
Distance between lac Z and lac A = (1 + 27 + 12) x 100 / (60 + 1 + 27 + 12)
= 40 x 100 / 100
= 40 m. u
Hence the genes lac Z and lac A are located 40 map units apart.
Distance between lac A and lac Y = (20 +1 +15) x 100 / (64 + 20 + 1 + 15)
= 36 x 100 / 100
= 36 m. u
Hence the genes lac A and lac Y are located 36 map units apart.
From the above results the gene order relative to trp E would be lac Z, lac Y and lac A. lac Y and lac Z are 41 map units apart, lac Z and lac A are 40 map units apart whereas lac A and lac Y are located 36 map units apart.
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