Problem 2 A cross is made between two E. coli strains: Hfr arg+ bio+ leu+ X F- a
ID: 39030 • Letter: P
Question
Problem 2 A cross is made between two E. coli strains: Hfr arg+ bio+ leu+ X F- arg- bio- leu-. Interrupted conjugation studies show that arg+ enters the recipient last, so arg+ recombinants are selected on a medium containing bio and leu only. These recombinants are tested for the presence of bio+ and leu+. The following numbers of individuals are found for each genotype: What is the gene order? What are the map distances in recombination units? Problem 3 In an interrupted conjugation experiment in E. col!, the pro gene enters after the thi gene. A pro+ thi+ Hfr is crossed with a pro? Thi? F? strain, and resulting exconjugants are plated on medium containing thiamine (thi) but no proline (pro). A total of 360 colonies are observed, and they are isolated and cultured on fully supplemented medium. These cultures are then tested for their ability to grow on medium containing no proline or thiamine (minimal medium), and 320 of the cultures are found to be able to grow but the remainder cannot. a. Deduce the genotypes of the two types of cultures. b. Draw the crossover events required to produce these genotypes. c. Calculate the distance between the pro and thi genes in recombination units.Explanation / Answer
PROBLEM 2;
WHEN TWO E.coli HFR STRAINS ARE INTRODUCED ,WHEN ACROSS IS MADE BETWEEN THEM
arg+ bio+,leu+ * +arg-bio-leu , thorugh intrrupted conjugation arg+ , enters the recipients last .
the recombinants are with arg+,genes are 48+8 = 56, arg and bio +leu- = 8 ,
so , the gene order will be arg+ bio+ leu+ arg- bi0 - leu-
MAP DISTANCES;
BETWEEN ARG+ AND LEU- 48+8/320=0.175
BETWEEN ARG+,BIO -, LEU - 8/320 = 0.15 ,
SO THE DISTANCE BETWEEN ARG AND LEU- IS 0.175 -0.15 = 0.025 CENTI MORGANS.
PROBLEM 3;
PRO+ THI+ CROSSED WITH PRO-THI- ,
GENOTYPES OF CULTURE ; STRAINS GROWN ONLY ON THIAMINE ,NO PROLINE 360
STRAINS GROWN BETWEEN NO PROLINE OR THIMANINE =340 , SO GENOTYPE WILL BE PRO+THI+HFR STRAIN.
CROSSOVER EVENTS;
PRO-THI +, PRO+ THI- , PRO+THI+, PRO-THI- = PRO+THI+ * PRO-THI-
THE RECOMBINANTS WILL BE PRO-THI+, PRO+THI-
MAP DISTANCE;
PRO AND THI GENES; GROWN ONLY ON THIAMINE ARE 360,NO THIAMINE OR PROLINE =340, SO 20 COLONIES HAVE PROLINE IN THIER GENOME.
TOTAL NUMBER OF COLONIES ARE 700
MAP DISTANCE BETWEEN GENES THIAMINE 360/700 = 0.51,MAP DISTANCE FOR PROLINE 20/700 = 0.02.
MAP DISTANCE BETWEEN THIAMINE AND PROLINE ARE 0.51-0.02=0.49 CENTIMORGANS
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