In a haploid yeast strain, eight recessive mutationswere found that resulted in a requirement for theamino acid lysine. All the mutations were found to revert at a frequency of about 1 × 10−6 except mutations5 and 6, which did not revert. Matings were madebetween a and α cells carrying these mutations. Theability of the resultant diploid strains to grow onminimal medium in the absence of lysine is shown inthe following chart (+ means growth and − means nogrowth.)1 2 3 4 5 6 7 81 − + + + + − + −2 + − + + + + + +3 + + − − − − − +4 + + − − − − − +5 + + − − − − − +6 − + − − − − − −7 + + − − − − − +8 − + + + + − + −a. How many complementation groups were revealedby these data? Which point mutations are foundwithin which complementation groups?The same diploid strains are now induced to undergosporulation. The vast majority of resultant spores areauxotrophic; that is, they cannot form colonies whenplated on minimal medium (without lysine). However,particular diploids can produce rare spores that doform colonies when plated on minimal medium (prototrophic spores). The following table shows whether(+) or not (−) any prototrophic spores are formedupon sporulation of the various diploid cells.1 2 3 4 5 6 7 81 − + + + + − + +2 + − + + + + + +3 + + − + − + + +4 + + + − − − + +5 + + − − − − + +6 − + + − − − + +7 + + + + + + − +8 + + + + + + + −b. When prototrophic spores occur during sporulationof the diploids just discussed, what ratio of auxotrophic to prototrophic spores would you generallyexpect to see in any tetrad containing such a prototrophic spore? Explain the ratio you expect.c. Using the data from all parts of this question, drawthe best map of the eight lysine auxotrophic mutations under study. Show the extent of any deletionsinvolved, and indicate the boundaries of the various complementation groups.
In a haploid yeast strain, eight recessive mutations
were found that resulted in a requirement for theamino acid lysine. All the mutations were found to revert at a frequency of about 1 × 10−6 except mutations
5 and 6, which did not revert. Matings were made
between a and α cells carrying these mutations. The
ability of the resultant diploid strains to grow on
minimal medium in the absence of lysine is shown in
the following chart (+ means growth and − means no
growth.)
1 2 3 4 5 6 7 8
1 − + + + + − + −
2 + − + + + + + +
3 + + − − − − − +
4 + + − − − − − +
5 + + − − − − − +
6 − + − − − − − −
7 + + − − − − − +
8 − + + + + − + −
a. How many complementation groups were revealed
by these data? Which point mutations are found
within which complementation groups?
The same diploid strains are now induced to undergo
sporulation. The vast majority of resultant spores are
auxotrophic; that is, they cannot form colonies when
plated on minimal medium (without lysine). However,
particular diploids can produce rare spores that do
form colonies when plated on minimal medium (prototrophic spores). The following table shows whether
(+) or not (−) any prototrophic spores are formed
upon sporulation of the various diploid cells.
1 2 3 4 5 6 7 8
1 − + + + + − + +
2 + − + + + + + +
3 + + − + − + + +
4 + + + − − − + +
5 + + − − − − + +
6 − + + − − − + +
7 + + + + + + − +
8 + + + + + + + −
b. When prototrophic spores occur during sporulation
of the diploids just discussed, what ratio of auxotrophic to prototrophic spores would you generally
expect to see in any tetrad containing such a prototrophic spore? Explain the ratio you expect.
c. Using the data from all parts of this question, draw
the best map of the eight lysine auxotrophic mutations under study. Show the extent of any deletions
involved, and indicate the boundaries of the various complementation groups.
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