Page 106 - Genetics_From_Genes_to_Genomes_6th_FULL_Part2

Problems 265

and right of ry, respectively. These females are amino acid lysine. All the mutations were found to re-
−6
now mated to males homozygous for ry . Out of vert at a frequency of about 1 × 10 except mutations
41
100,000 progeny, 8 have wild-type eyes, Lyra wings, and 5 and 6, which did not revert. Matings were made
Stubble bristles, while the remainder have rosy eyes. b etween a and α cells carrying these mutations. The
a. What is the order of these two ry mutations relative ability of the resultant diploid strains to grow on
to the flanking genes Ly and Sb? minimal medium in the absence of lysine is shown in
564
41
b. What is the genetic distance separating ry and ry ? the following chart (+ means growth and − means no
growth.)
−
34. Nine rII mutants of bacteriophage T4 were used in
pairwise infections of E. coli K(λ) hosts. Six of the 1 2 3 4 5 6 7 8
mutations in these phages are point mutations; the 1 − + + + + − + −
other three are deletions. The ability of the doubly in- 2 + − + + + + + +
fected cells to produce progeny phages in large num- 3 + + − − − − − +
bers is scored in the following chart. 4 + + − − − − − +
5 + + − − − − − +
1 2 3 4 5 6 7 8 9
6 − + − − − − − −
1 − − + + − − − + +
7 + + − − − − − +
2 − + + − − − + +
8 − + + + + − + −
3 − − + − + − −
4 − + − + − − a. How many complementation groups were revealed
5 − − − + + by these data? Which point mutations are found
6 − − − − within which complementation groups?
7 − + + The same diploid strains are now induced to undergo
8 − − sporulation. The vast majority of resultant spores are
9 −
auxotrophic; that is, they cannot form colonies when
The same nine mutants were then used in pairwise in- plated on minimal medium (without lysine). However,
fections of E. coli B hosts. The production of progeny particular diploids can produce rare spores that do
phages that can subsequently lyse E. coli K(λ) hosts is form colonies when plated on minimal medium (pro-
now scored. In the table, 0 means the progeny do not totrophic spores). The following table shows whether
produce any plaques on E. coli K(λ) cells; − means (+) or not (−) any prototrophic spores are formed
that only a very few progeny phages produce plaques; upon sporulation of the various diploid cells.
and + means that many progeny produce plaques
(more than 10 times as many as in the − cases). 1 2 3 4 5 6 7 8
1 − + + + + − + +
1 2 3 4 5 6 7 8 9 2 + − + + + + + +
1 − + + + + − − + + 3 + + − + − + + +
2 − + + + + − + + 4 + + + − − − + +
3 0 − + 0 + + − 5 + + − − − − + +
4 − + − + + + 6 − + + − − − + +
5 − + − + + 7 + + + + + + − +
6 0 0 − + 8 + + + + + + + −
7 0 + +
8 − + b. When prototrophic spores occur during sporulation
9 − of the diploids just discussed, what ratio of auxo-
trophic to prototrophic spores would you generally
a. Which of the mutants are the three deletions? What expect to see in any tetrad containing such a proto-
criteria did you use to reach your conclusion? trophic spore? Explain the ratio you expect.
b. If you know that mutation 9 is in the rIIB gene, c. Using the data from all parts of this question, draw
draw the best genetic map possible to explain the the best map of the eight lysine auxotrophic muta-
data, including the positions of all point mutations tions under study. Show the extent of any deletions
and the extent of the three deletions. involved, and indicate the boundaries of the vari-
c. One uncertainty should remain in your answer to ous complementation groups.
part (b). How could you resolve this uncertainty? 36. In Problem 24, you learned that Bloom syndrome is
35. In a haploid yeast strain, eight recessive mutations an autosomal recessive disease characterized by the
were found that resulted in a requirement for the high frequency of harlequin chromosomes (as