. Imagine that you have done a cross between twostrains of yeast, one of which has the genotype A B Cand the other a b c, where the letters refer to threerather closely linked genes in the order given. Youexamine many tetrads resulting from this cross, andyou find two that do not contain the expected two Band two b spores. In tetrad I, the spores are A B C, AB C, a B c, and a b c. In tetrad II, the spores are A BC, A b c, a b C, and a b c. How have these unusualtetrads arisen?

. Imagine that you have done a cross between twostrains of yeast, one of which has the genotype A B Cand the other a b c, where the letters refer to threerather closely linked genes in the order given. Youexamine many tetrads resulting from this cross, andyou find two that do not contain the expected two Band two b spores. In tetrad I, the spores are A B C, AB C, a B c, and a b c. In tetrad II, the spores are A BC, A b c, a b C, and a b c. How have these unusualtetrads arisen?

Concepts of Biology

1st Edition

ISBN:9781938168116

Author:Samantha Fowler, Rebecca Roush, James Wise

Publisher:Samantha Fowler, Rebecca Roush, James Wise

Chapter7: The Cellular Basis Of Inheritance

Section: Chapter Questions

Problem 1ACQ: Figure 7.2 If a mutation occurs so that a fungus is no longer able to produce a minus mating type,...

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Imagine that you have done a cross between two strains of yeast, one of which has the genotype A B C and the other a b c, where the letters refer to three closely linked genes in the order given. You examine many tetrads resulting from this cross, and the two tetrads below are found that have atypical scoring patterns. In tetrad I, the spores are A B C, ABC, a B c, and a b c. In tetrad II, the spores are A B C, A b c, a b C, and a b c. Which tetrad or tetrads indicate(s) that gene conversion has occurred AND show(s) that recombination has occurred between genes A and C? O neither tetrads I and II O tetrad II O tetrad I O both tetrads I and II
. A geneticist working on a haploid fungus makes a cross between two slow-growing mutants called mossy and spider (referring to the abnormal appearance of the colonies). Tetrads from the cross are of three types (A, B, C), but two of them contain spores that do not germinate.Devise a model to explain these genetic results, and propose a molecular basis for your model.
The life cycle of the haploid fungus Ascobolus is similar tothat of Neurospora. A mutational treatment producedtwo mutant strains, 1 and 2, both of which when crossedwith wild type gave unordered tetrads, all of the followingtype (fawn is a light brown color; normally, crosses produce all black ascospores):spore pair 1 black spore pair 3 fawnspore pair 2 black spore pair 4 fawna. 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 fawnspore pair 2 fawn spore pair 4 fawnb. What does this result suggest? Explain.When large numbers of unordered tetrads were screenedunder the microscope, some rare ones that containedblack spores were found. Four cases are shown here:Case A Case B Case C Case Dspore pair 1 black black black blackspore pair 2 black fawn black abortspore pair 3 fawn fawn abort fawnspore pair 4 fawn fawn abort fawn(Note: Ascospores with extra genetic material…
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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…
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Figure 7.2 If a mutation occurs so that a fungus is no longer able to produce a minus mating type, will it still be able to reproduce? Figure 7.2 (a) In animals, sexually reproducing adults form haploid gametes from diploid germ cells. (b) Fungi, such as black bread mold (Rhizopus nigricans), have haploid-dominant life cycles. (c) Plants have a life cycle that alternates between a multicellular haploid organism and a multicellular diploid organism. (credit c fern: modification of work by Cory Zanker; credit c gametophyte: modification of work by Vlmastra/Wikimedia Commons)
JA yeast proline, histidine auxotroph is mated with a prototroph and the diploid cell is sporulated. a.) Write out the cross that generated the diploid cell? b. ) List the types of tetrads and the genotypes of each spore in the tetrad that will occur if this diploid cell is sporulated.
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Options for 1 & 3 & 5 -2n+2n -n -n+n -2n options for 2 & 4 -haploid -dipoid -dikaryotic options for bottom chart are A, B, C
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