Concept explainers
If you expose human tissue culture cells (for example, HeLa cells) to 3H-thymidine just as they enter S phase, then wash this material off the cells and let them go through a second S phase before looking at the chromosomes, how would you expect the 3H to be distributed over a pair of homologous chromosomes? (Ignore the effect recombination could have on this outcome.) Would the radioactivity be in (a) one chromatid of one homolog, (b) both chromatids of one homolog, (c) one chromatid each of both homologs, (d) both chromatids of both homologs, or (e) some other pattern? Choose the correct answer and explain your reasoning. (This problem extends the analysis begun in Solved Problem III on p. 201.)
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Genetics: From Genes to Genomes, 5th edition
- Baker's yeast, Saccharomyces cerevisiae, is a single-celled, diploid fungus (which is, of course, a eukaryote, that is capable of both meiosis and sexual reproduction). Wild type yeast can normally grow on solid or liquid minimal medium; you isolate three mutant strains which are no longer capable of growing on minimal medium alone, however, they can grow on medium supplemented with adenine. All three yeast strains are homozygous for the underlying alleles. When you cross mutant strain 1 and mutant strain 2, the offspring cannot grow on minimal medium alone and require adenine supplementation; when you cross mutant strain 1 and mutant strain 3, the offspring can grow on minimal medium alone and do not require adenine. A. What conclusions can you make about the alleles of mutant strains 1, 2, and 3 and their relationships with each other? B. What phenomenon is occurring in the cross between mutant strains 1 and 3?arrow_forwardThe 3′ → 5′ exonuclease activity of Pol I excises only unpaired 3′-terminal nucleotides from DNA, whereas this enzyme’s pyrophosphorolysis activity removes only properly paired 3′-terminal nucleotides. Discuss the mechanistic signifi cance of this phenomenon in terms of the polymerase reaction.arrow_forwardIdentify the single most correct choice: a) DNA replication is a non-conservative process. b) Peroxide and ozone can be used as antimicrobial agents and their mechanism of action is via oxidizing molecules inside the cells. c) Antibiotics can never be used as food preservatives. d) All of the above.arrow_forward
- An Hfrstrain that is a *b*c*d* e*f* g *h* is mated with an F strain that is a b e d e f gh. The mating is interrupted at 5 minutes interval, and the genotypes of the F recombinants are determined. The results obtained are tabulated in Table 2. Draw the map of the Hfrchromosome and indicate the position of the origin of transfer, the direction of the transfer and the minutes between genes. Table 2:Entry time of Hfr chromosome into recipient cell. Time a d e f h 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +arrow_forwardWhat do you mean by Error-Prone Repair by Nonhomologous End Joining?arrow_forwardAcridine orange is a chemical that inhibits the replication ofF- factor DNA but does not affect the replication of chromosomalDNA, even if the chromosomal DNA contains an Hfr. Let’s supposethat you have an E. coli strain that is unable to metabolizelactose and has an F factor that carries a streptomycin-resistantgene. You also have an F− strain of E. coli that is sensitive to streptomycinand has the genes that allow the bacterium to metabolize lactose. This second strain can grow on a lactose-containing medium.How would you generate an Hfr strain that is resistant tostreptomycin and can metabolize lactose? (Hint: F factors occasionally integrate into the chromosome to become Hfr strains, and occasionally Hfr strains excise their DNA from the chromosome to become F+ strains that carry an F′ factor.)arrow_forward
- Why evenly spaced sequence in chromatogram is an indication of a good DNA chromatogram?arrow_forwardThe E. coli chromosome is 1.28 mm long. Under optimal conditions, thechromosome is replicated in 40 minutes.(a) What is the distance traversed by one replication fork in 1 minute?(b) If replicating DNA is in the B form (10.4 base pairs per turn), how manynucleotides are incorporated in 1 minute in one replication fork?(c) If cultured human cells (such as HeLa cells) replicate 1.2 m of DNAduring a five-hour S phase and at a rate of fork movement one-tenthof that seen in E. coli, how many origins of replication must the cellscontain?(d) What is the average distance, in kilobase pairs, between these origins?arrow_forwardA chromosome from a multicellular slime mold called purple oblex (Plasmodiophora oblexii) is 13% adenine (A), what is the percentage of guanine (G)?arrow_forward
- What do you mean by conjugation? Give some example.arrow_forwardYou have used the technique of chromatin immunoprecipitation to isolate DNA fragments containing a DNA-binding protein of interest. Suppose that you wish to know whether a particular known DNA fragment is present in the isolated mixture. How might you detect its presence?arrow_forwardSupercoiled DNA is slightly unwound compared to relaxed DNA and this enables it to assume a more compact structure with enhanced physical stability. Describe the enzymes that control the number of supercoils present in the E. coli chromosome. How much would you have to reduce the linking number to increase the number of supercoils by five?arrow_forward
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