Case A Case B Case C Case D spore pair 1 spore pair 2 spore pair 3 spore pair 4 black black black black black fawn black abort fawn fawn abort fawn fawn fawn abort fawn (Note: Ascospores with extra genetic material survive,
The life cycle of the haploid
that of Neurospora. A mutational treatment produced
two mutant strains, 1 and 2, both of which when crossed
with wild type gave unordered tetrads, all of the following
type (fawn is a light brown color; normally, crosses produce all black ascospores):
spore pair 1 black spore pair 3 fawn
spore pair 2 black spore pair 4 fawn
a. What does this result show? Explain.
The two mutant strains were crossed. Most of the unordered tetrads were of the following type:
spore pair 1 fawn spore pair 3 fawn
spore pair 2 fawn spore pair 4 fawn
b. What does this result suggest? Explain.
When large numbers of unordered tetrads were screened
under the microscope, some rare ones that contained
black spores were found. Four cases are shown here:
Case A Case B Case C Case D
spore pair 1 black black black black
spore pair 2 black fawn black abort
spore pair 3 fawn fawn abort fawn
spore pair 4 fawn fawn abort fawn
(Note: Ascospores with extra genetic material survive,
but those with less than a haploid genome abort.)
c. Propose reasonable genetic explanations for each of
these four rare cases.
d. Do you think the mutations in the two original
mutant strains were in one single gene? Explain.
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