Question

A circular plasmid of 6.0 kB was cleaved with the restriction enzymes EcoRI, BamHI and PstI.  Cleavage with each enzyme alone gave a single band of 6.0 kB for BamHI and PstI, and a single band of 3.0 kB for EcoRI.  When BamHI and PstI were used together for the digest, bands of 1.5 and 4.5 were observed, and when BamHI and EcoRI were used together only the 3.0 kB band was observed.  What do you predict will be the pattern generated by treating the plasmid with both EcoRI and PstI?

Select one:

a. A 4.5, a 3 and a 1.5 kb band

b. The information does not allow a unique prediction to be made

c. A 4.5 and 1.5 kB band

d. A 3.0 and a 1.5 kB band

e. A 6 kB band

A testcross was done between a lily heterozygous for the genes a, b and c, and a triply recessive tester strain.  The resulting phenotypes were scored for 1000 progeny, and this analysis gave the following distribution of phenotypic classes

a+ b+ c+          23

a+ b+ c            230

a+ b c+            24

a+ b c               220

a b+ c+            228

a b+ c               26

a b c                 27

a b c+              222

What is the distance between a and b?  Chose the best answer

Select one:

a. between 20.1 and 25 cM

b. a and b are so tightly linked they show no recombination

c. a and b are unlinked

d. between 0.1 and 13 cM

e. between 13.1 and 20 cM

A testcross was done between a lily heterozygous for the genes a, b and c, and a triply recessive tester strain.  The resulting phenotypes were scored for 1000 progeny, and this analysis gave the following distribution of phenotypic classes

a+ b+ c+          23

a+ b+ c            230

a+ b c+            24

a+ b c               220

a b+ c+            228

a b+ c               26

a b c                 27

a b c+              222

What is the distance between a and c?  Chose the best answer

Select one:

a. a and b are so tightly linked they show no recombination

b. between 13.1 and 20 cM

c. between 0.1 and 13 cM

d. between 20.1 and 25 cM

e. a and b are unlinked

Answer 1

1. The correct answer is option 'c'. Two bands will be generated, one of length 4.5bp and one of length 1.5 bp. The EcoRI will cut the exzyme at one site and pstI at another, the restriction site of EcoRI and BamHI is same, and hence, the above two fragments will be generated.

2. The recombination frequency for gnes a and b is approximately 50%, which means that the genes a and b are unlinked. Hence, the correct answer is option 'c'.

3. The recombination frequency for gnes a and c is 67%, which means that the genes a and c are not linked and most likely are on different chromosomes. Hence, the correct answer is option 'e'.