In a three-point cross, individuals homozygous for wild type alleles at three lo
ID: 79280 • Letter: I
Question
In a three-point cross, individuals homozygous for wild type alleles at three loci (w^+w^+c^+c^+p^+p^+) were crossed with individuals homozygous recessive for all three genes (ww cc pp). The F_1 are crossed to ww cc pp individuals and produce the following genotypes: Determine the order and map distances between these genes. A. Order: w-c-p; w-c distance = 4.3 map units; c-p distance = 2.9 map units. B. Order: p-w-c; p-w distance = 4.3 map units; w-c distance = 2.9 map units. C. Order: p-c-w; p-c distance = 2.9 map units c-w distance = 4.3 map units. D. Order: c-w-p; c-w distance = 4.3 map units; w-p distance = 2.9 map units. E. Order: p-w-c; p-w distance = 4.0 map units; w-c distance = 2.6 map units. Which of the following events does not take place during conjugation in bacteria?Explanation / Answer
Answer: B. order: p-w-c; p-w distance = 4.3 map units; w-c distance = 2.9 map units
Explanation:
Usually parental combinations will be more than the recombinants, so the arrangement of genes in heterozygous condition is w+ c+ p+ / w c p
1. If single cross over (SCO) occurs between w+ & c+ and w & c
Normal order= w+---------c+ & w-----c
After cross over= w+-----c & w------c+
w+-----c recombinants are 12+2 = 14
w------c+ recombinants are 14+1 = 15
Total recombinants = 29
RF = (29/1000.)*100 =2.9 %
2. If single cross over (SCO) occurs between c+ & p+ and c & p
Normal order= c+---------p+ & c----p
After cross over= c+-----p & c------p+
c+-----p recombinants are 21+14 = 35
c------p+ recombinants are 19+12 = 31
Total recombinants = 66
RF = (66 / 1000)*100 = 6.6%
3. If single cross over (SCO) occurs between w+ & p+ and w & p
Normal order= w+---------p+ & w------p
After cross over= w+-----p & w------p+
w+-----p recombinants are 21+2 = 23
w------p+ recombinants are 19+1 = 20
Total recombinants = 43
RF = (43/1000)*100 =4.3%
% RF = Map unit distance
The order of genes is -----
c---2.9 m.u.---w-----4.3m.u.-----p
Order of genes is c-w-p or p-w-c
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