Genetics: From Genes to Genomes
6th Edition
ISBN: 9781259700903
Author: Leland Hartwell Dr., Michael L. Goldberg Professor Dr., Janice Fischer, Leroy Hood Dr.
Publisher: McGraw-Hill Education
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Chapter 6, Problem 31P
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 rather closely linked genes in the order given. You examine many tetrads resulting from this cross, and you find two that do not contain the expected two B and two b spores. In tetrad I, the spores are A B C, A B C, 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. How have these unusual tetrads arisen?
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You cross two yeast strains one is an ade auxotroph the other is a pro auxotroph and allow
the diploid to sporulate. When you score each spore in the ascus you find the following
proportions: 518 PD, 8 NPD, and 225 T.
a.) What are the genotypes of each spore in all three types of the tetrads.
b) Are these genes linked why or why not?
c.) If these genes are unlinked what would you expect the progeny numbers and ratios to
be?
d.) What is the formula to determine the most accurate distance between these genes? If
linked what is the map distance?
A cross between yeast strains ab x AB produces the following unordered tetrads:
a. Label each group of tetrads as parental ditypes (PD), non-parental ditypes (NPD), or
tetratypes (T).
AB
AB
ab
ab
43
6
22
b. Are the genes linked or on separate chromosomes? Why?
aB
aB
Ab
Ab
Ab
AB
ab
aB
c. If the genes are linked determine the distance between them.
Neurospora of genotype a + c are crossed withNeurospora of genotype + b +. (Here, + is shorthandfor the wild-type allele.) The following tetrads areobtained (note that the genotype of the four sporepairs in an ascus are listed, rather than listing alleight spores):a + c a b c + + c + b c a b + a + ca + c a b c a + c a b c a b + a b c+ b + + + + + b + + + + + + c + + ++ b + + + + a b + a + + + + c + b +137 141 26 25 2 3a. In how many cells has meiosis occurred to yieldthese data?b. Give the best genetic map to explain these results.Indicate all relevant genetic distances, both betweengenes and between each gene and the centromere.c. Diagram a meiosis that could give rise to oneof the three tetrads in the class at the far right inthe list
Chapter 6 Solutions
Genetics: From Genes to Genomes
Ch. 6 - Griffith, in his 1928 experiments, demonstrated...Ch. 6 - Griffith, in his 1928 experiments, demonstrated...Ch. 6 - During bacterial transformation, DNA that enters a...Ch. 6 - Nitrogen and carbon are more abundant in proteins...Ch. 6 - If 30 of the bases in human DNA are A, a what...Ch. 6 - Which of the following statements are true about...Ch. 6 - Imagine you have three test tubes containing...Ch. 6 - What information about the structure of DNA was...Ch. 6 - A portion of one DNA strand of the human gene...Ch. 6 - When a double-stranded DNA molecule is exposed to...
Ch. 6 - A particular virus with DNA as its genetic...Ch. 6 - The underlying structure of DNA is very simple,...Ch. 6 - Prob. 13PCh. 6 - Bacterial transformation and bacteriophage...Ch. 6 - The CAP protein is shown bound to DNA in Fig....Ch. 6 - In Meselson and Stahls density shift experiments...Ch. 6 - When Meselson and Stahl grew E. coli in 15N medium...Ch. 6 - If you expose human tissue culture cells for...Ch. 6 - Draw a replication bubble with both replication...Ch. 6 - a. Do any strands of nucleic acid exist in nature...Ch. 6 - As Fig. 6.21 shows, DNA polymerase cleaves the...Ch. 6 - The bases of one of the strands of DNA in a region...Ch. 6 - Replicating structures in DNA can be observed in...Ch. 6 - Indicate the role of each of the following in DNA...Ch. 6 - Draw a diagram of replication that is occurring at...Ch. 6 - Figure 6.18 depicts Watson and Cricks initial...Ch. 6 - Researchers have discovered that during...Ch. 6 - A DNA synthesizer is a machine that uses automated...Ch. 6 - Bacterial cells were coinfected with two types of...Ch. 6 - A yeast strain with a mutant spo11- allele has...Ch. 6 - Imagine that you have done a cross between two...Ch. 6 - The Neurospora octad shown came from a cross...Ch. 6 - From a cross between e f g and e f g strains of...Ch. 6 - In Step 6 of Fig. 6.27, the resolvase enzyme...Ch. 6 - Figure 6.31shows four potential outcomes of...Ch. 6 - Each of the substrates for site-specific...Ch. 6 - Prob. 37PCh. 6 - Suppose that you could inject a wild-type mouse...Ch. 6 - C31 is a type of bacteriophage that infects...Ch. 6 - Cre is a recombinase enzyme encoded by a gene in...Ch. 6 - Like Cre/loxP recombination, site-specific...
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- From a cross between e+ f+ g+ and e− f − g− strains ofNeurospora, recombination between these linkedgenes resulted in a few octads containing the followingordered set of spores:e+ f+ g+e+ f+ g+e+ f − g+e+ f − g+e− f − g−e− f − g−e− f − g−e− f − g−a. Where was recombination initiated?b. Did crossing-over occur between genes e and g?Explain.c. Why do you end up with 2 f+ : 6 f − but 4 e+: 4 e−and 4g+: 4g−?d. Could you characterize these unusual octads as MIor MII for any of the three genes involved?Explain.arrow_forwardA heterozygous diploid yeast Aa Bb went through meiosis. What percentage of the haploid spores will have recombinant combinations of alleles? What if genes A and B are unlinked? Explain What is genes A and B are linked? Explainarrow_forwardOne yeast strain carries the alleles lys+ and arg+, whereas another strain has lys-3 and arg-2. The two strains were crossed toeach other, and an ascus obtained from this cross has four spores with the following genotypes: lys+ arg+, lys+ arg-2, lys-3arg+, and lys-3 arg 2. This ascus has a. a parental ditype.b. a tetratype.c. a nonparental ditype.d. either a tetratype or a nonparental ditype.arrow_forward
- A Neurospora colony at the edge of a plate seemed to be sparse (low density) in comparison with the other colonies on the plate. This colony was thought to be a possible mutant, and so it was removed and crossed with a wild type of the opposite mating type. From this cross, 100 ascospore progeny were obtained. None of the colonies from these ascospores was sparse, all appearing to be normal. What is the simplest explanation of this result? How would you test your explanation? (Note: Neurospora is haploid.)arrow_forwardJA 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.arrow_forwardIn an electrophoretic gel across which is applied a powerful electrical alternating pulsed field, the DNA of the haploid fungus Neurospora crassa (n = 7) moves slowly but eventually forms seven bands, which represent DNA fractions that are of different sizes and hence have moved at different speeds. These bands are presumed to be the seven chromosomes. How would you show which band corresponds to which chromosome?arrow_forward
- his-l and lys-3 are alleles found in baker's yeast that require histidine and lysine for growth, respectively. A cross was made between two haploid yeasts that are his-1 lys-3 and his lys". From the analysis of 900 individual tetrads, the following numbers of tetrads were obtained: GI: 2 spores are his-1 lys* +2 spores are his* lys-3 = 8 G2: 2 spores are his-1 lys-3+ 2 spores are his* lys* = 512 G3: 1 spore is his-1 lys-3 +1 spore is his-1 lys + 1 spore is his lys-3+ 1 spore is his" lys = 380 (i) Name the ascus type of each group as P, NP or T. (ii) Are the genes linked? Explain your answer. (iii) If the genes are linked, calculate the distance between the genes.arrow_forwardOn chromosome 4 in Nuerospora, the allele pyr-1 results in a pyrimidine requirement for growth. A cross is made between a pyr-1 and pyr+ strain and the following results were obtained: 26 of a 2:4:2 pattern of pyr-1:pyr+:pyr-1 25 of a 2:4:2 pattern of pyr+:pyr-1:pyr+ 24 of a 2:2:2:2 pattern of pyr-1:pyr+:pyr-1:pyr+ 457 of a 4:4 pattern of pyr-1:pyr+ 27 of a 2:2:2:2 pattern of pyr+:pyr-1:pyr+:pyr-1 452 of a 4:4 pattern of pyr+:pyr-1 What is the distance of the pyr locus to the centromere? Show your work.arrow_forwardIndicate the percentage of tetrads that would have 0,1, 2, 3, or 4 viable spores after Saccharomycescerevisiae a / α diploids of the following genotypesare sporulated:a. A true-breeding wild-type strain (with no mutations in any gene essential for viability).b. A strain heterozygous for a null (completely inactivating) mutation in a single essential gene.For the remaining parts of this problem, considercrosses between yeast strains of the form a × b, wherea and b are both temperature-sensitive mutations indifferent essential genes. The cross is conducted under permissive (low-temperature) conditions. Indicatethe percentage of tetrads that would have 0, 1, 2, 3, or4 viable spores subsequently measured under restrictive (high-temperature) conditions.c. a and b are unlinked, and both are 0 m.u. from thecentromere.d. a and b are unlinked; a is 0 m.u. from the centromere, while b is 10 m.u. from the centromere.e. a and b are 0 m.u. apart.f. a and b are 10 m.u. apart. Assume all…arrow_forward
- A cross was performed between a yeast strain that requires methionine and lysine for growth (met− lys−)and another yeast strain, which is met+ lys+. One hundred asci were dissected, and colonies were grownfrom the four spores in each ascus. Cells from thesecolonies were tested for their ability to grow on petriplates containing either minimal medium (min), min+ lysine (lys), min + methionine (met), or min + lys+ met. The asci could be divided into two groupsbased on this analysis:Group 1: In 89 asci, cells from two of the four spore colonies couldgrow on all four kinds of media, while the other two spore coloniescould grow only on min + lys + met.Group 2: In 11 asci, cells from one of the four spore colonies couldgrow on all four kinds of petri plates. Cells from a second one ofthe four spore colonies could grow only on min + lys plates andon min + lys + met plates. Cells from a third of the four sporecolonies could only grow on min + met plates and on min + lys+ met. Cells from the…arrow_forwardTwo haploid strains of S. cerevisae (yeast) are crossed. One has the genotype ABC and the other abc. Five sets of the resultant tetrads are noted below. In which set did a gene conversion event occur? Look for a 1:3 or 3:1 ratio A) abc, aBc, AbC, aBC a/A is 3 recessive 1dominant, B/b is 2:2, same for C B) abc, abc, ABC, ABC 2:2 for all C) aBc, aBc, AbC, AbC 2:2 for all D) abC, abc, ABc, ABC this one has equal ratio of dominant/recessive 2 dominant C’s, 2 Recessive c, same form A and a and B and b. E) Abc, Abc, aBC, aBCarrow_forwardAlloploids are produced by crosses involving two different species. Explain why alloploids may be reproductively isolated from the two original species from which they were derived. Explain why alloploids are usually sterile, whereas allotetraploids (containing a diploid set from each species) are commonly fertile.arrow_forward
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