Category: CSIR NET Life Science Previous Year Questions and Solution on MICROBIAL GENETICS

Category: CSIR NET Life Science Previous Year Questions and Solution on MICROBIAL GENETICS

CSIR NET Life Science Previous Year Questions and Solution on MICROBIAL GENETICS

39. An E. coli strain has metB1 (90 min) and leuA5 (2 min) mutations. It also has strA7 (73 min) mutation and Tn5 transposon which confers streptomycin and kanamycin resistance, respectively, inserted in its chromosome. The mutant strain was crossed with an Hfr strain that is streptomycin sensitive and has a hisG2 mutation (44 min) that makes it require histidine. After incubation for 100 min, the cells were plated on minimal plate supplemented with leucine, histidine and streptomycin to select the metB marker. After purifying 100 of the Met+ transconjugants, one finds that 15 are His+, 2 are Leu+ and 12 are kanamycin sensitive. The unselected markers are A. metB1 and leuA5 mutation. B. leuA5 and Tn5 insertion mutation. Which of the above statement is correct and what is the position of transposon insertion? (1) A and before 73 min (2) B and before 44 min (3) B and before 73 min (4) A and before 44 min

Hfr Conjugation Unselected Markers

38. A conjugation experiment is carried out between F+ his+ leu+ thr+ pro+ bacteria and F- his- leu- thr- pro- bacteria for a period of 25 minutes. At this time the mating is stopped, and the genotypes of the recipient F- bacteria are determined. The results are shown below: Genotype Number of colonies his+ 0 leu+ 13 thr+ 26 pro+ 6 What is the probable order of these genes on the bacterial chromosome? (1) thr, leu, pro, his (2) pro,leu, thr and the position of his cannot be determined. (3) thr, leu, pro, and the position of his cannot be determined (4) his, pro, leu, thr 38. A conjugation experiment is carried out between F+ his+ leu+ thr+ pro+ bacteria and F- his- leu- thr- pro- bacteria for a period of 25 minutes. At this time the mating is stopped, and the genotypes of the recipient F- bacteria are determined. The results are shown below: Genotype Number of colonies his+ 0 leu+ 13 thr+ 26 pro+ 6 What is the probable order of these genes on the bacterial chromosome? (1) thr, leu, pro, his (2) pro,leu, thr and the position of his cannot be determined. (3) thr, leu, pro, and the position of his cannot be determined (4) his, pro, leu, thr

Bacterial Conjugation Gene Order Mapping

37. Using interrupted mating, four Hfr strains were analysed for the sequence in which they transmitted a number of different genes to a F- strain. Each Hfr strain was found to transmit its genes in a unique order as summarized in the table (Only the first five genes were scored) Order of transmission Hfr strain 1 2 3 4 First A B M F B A K H D L J G F M G J Last H K H K Which one of the following correctly represents the gene sequence in the original strain from which the Hfr strain were derived as well as the place of integration and polarity of the F plasmid?

Interrupted Mating Hfr Mapping Problem

36. In E. coli four Hfr strains donate the following genet, t markers in the order shown below: Strain 1: L Q W X Y Strain 2: M T A D Y Strain 3: E C M T A Strain 4: W Q L E C Which of the following depicts the correct order of the markers and the site of integration () of the F- factor in the four Hfr strains?

Hfr Mapping in E. coli

35. In E. coli. four Hfr strains donate the genetic markers shown in the order shown: Strain 1: F L K O Z Strain 2: C Y A Z O Strain 3: P D W C Y Strain 4: P F L K O All the Hfr strains are derived from the same F+ strain. What is the order of these markers on the chromosome of the original E. coli F+ strain? (1) K O Z P D F L W C Y A K (2) F L K O Z P D W C Y A F (3) F L K O Z A Y C W D P F (4) F L K C Y A Z O W D P F

E. coli Hfr Strains Chromosome Mapping

34. In a conjugation experiment between bacterial Hfr strain 'X' and F-cell, lac gene enters the recipient in 4 minutes, but the F-cells remain auxotrophic for Leu, Trp, Ura, Glu,Phe and Gly. The mating is then allowed to proceed for 20 minutes and lac+ exconjugants are selected. Of the lac+ cells, 35% are leu+ 98% are trp+ 10% are ura+ 65% are glu+ 0% are phe+ 81% are gly+ Select the correct order of the genes as they enter, from the choices given below (1) trp, gly, glu, leu. ura, phe+ lac+ (2) lact phet ura+, leu+, glu+, gly+, trp+ (3) phe; ura+, leu+, glu, gly, trp, Lact (4) lac+,trp+, gly+, glu+, lau+, ura+, phe+

Understanding Gene Order in Bacterial Hfr Conjugation

33. A cross is mode between an Hfr strain that is met+ thi+ pur+ and an F- that is met- thi- pur-. The recombinants are selected on medium that contains supplements that satisfy only the requirements for pur and thi and not for met. These recombinants are tested for the presence of the thi+ and pur+ alleles. The following number of colonies are found for each genotype: met+ thi+ pure+ 200 met+ thi+ pur- 0 met+ thi- pur+ 7 met+ thi- pur- 60 What is the order of genes in Hfr strain? (1) met+ pur+ thi+ (2) met+ thi+ pur+ (3) thi+ met+ pur+ (4) pur+ met+ thi+

Hfr Gene Order Mapping

32. A cross was made between Hfr met+ arg+ leu+ strs X F- met- arg- leu- strr in which leu+ exconjugants are selected. If the linear organization of the genes are leu+ arg+ met+, which one of the following genotypes is expected to occur in the lowest frequency? (1) leu+ arg- met- (2) leu+ arg+ met- (3) leu+ arg+ met- (4) leu+ arg- met+

Hfr Conjugation Gene Mapping

31. Two Hfr strains, Hfr-1 (arg+leu+ gal+strS) and Hfr-2 (arg+ his+ gal+ pur+ strs) were mated with a F- strain (arg-leu- gal- his-pur-strs). The results of the interrupted mating experiment are shown as plots 'a' and ‘b’, respectively. Based on these results, identify which of the options accurately reflects the order of loci?

Interrupted Mating Mapping

30. Four different Hfr strains of E. coli were mated with F- recipients, and the time of entry of various donor markers were found to be as below: Hfr 1: met [15 min] thr [30 min] phe [42 min] mal [57 min] Hfr 2: bio [50 min] thy [51 min] his [60 min] mal [77 min] Hfr 3: cys [10 min] phe [26 min] his [58 min] Hfr4: his [12 min] bio [22 min] azi [27 min] thi [44min] Based upon the above observations, the following statements were made assuming met to be at 0 min and thr at 15 min: (A) his is located at 59 min (B) azi is located at 74 min (C) cys is located at 11 min (D) mal is located at 76 min Which one of the following options represents all correct statements? (1) A and D only (2) B, C and D (3) A, B and C (4) C and D only

Detailed Explanation of E. coli Hfr Strain Gene Mapping Using Time of Entry Data

29. Interrupted mating experiments were performed using three different Hfr strains (1-3). The three strains have different combinations of selectable markers. The time of entry for markers for each strain is shown is shown in the table given. Strain Time of entrry Hfr #1 met (5’) thr (17’) strr (25’) phe (30’) pro (45’) Hfr #2 Strr (15’) Purr (28’) pro (35’) his (45’) met (55’) Hfr #3 pro (2’) his (12’) met (22’) Strr (42’) phe (47’) Using the above data, predict the correct sequence of markers on the E. coli chromosome. (1) met-thr-strr-phe-pro-purr-his (2) purr-pro-his-met-thr-strr-phe (3) strr-purr-his-met-phe-pro-strr (4) his-met-phe-thr-pro-strr-purr

Interrupted mating mapping in E. coli

28. The following table shows mapping data from three interrupted mating experiments using three different Hfr strains and an F- strain: Appearance of gene in F- cells (Time is represented in minutes) The following answers are derived: A. e g b d c f B. f g b d c e The distance between C. f and g is 32 min and between f and b is 30 min D. c and e is 28 min and between b and c is 20 min The correct combination of answer is (1) A, C and D (2) B and C (3) A and B (4) B and D

Interrupted Mating Mapping in E. coli

27. An interrupted mating experiment was performed between Hfr strs a+b+c+ and F- strr a-b-c- strains. The genotype of majority of streptomycin resistant (strr) exconjugant after 10,20, and 30 minutes of interrupted mating is given below: 10 min a+b-c- 20 min a+b-c+ 30 min a+b+c+ The most probable gene order would be (1) a b c (2) c a b (3) b a c (4) a c b

Interrupted Mating Mapping Problem

26. The distance between bacterial genes as determined from interrupted mating experiments are measured in units of (1) cM (2) minutes (3) bp (4) micrometers

Understanding Gene Distance Measurement in Bacterial Interrupted Mating Experiments

25. Which one of the following is true for cells harbouring F+ plasmid? (1) Their F plasmid is non-functional. (2) They exhibit increased rates of transfer of all chromosomal genes. (3) They are merodiploids. (4) They fail to survive as the chromosomal origin of replication is inactivated.

Understanding the True Characteristics of Cells Harboring F+ Plasmid in Bacteria

24. Which one of the following is correct statement about the difference between a F+ cell and Hfr cell? (1) In F+ cell F factor is an integral part of bacterial chromosome, while in Hfr cell F factor is present as an episome. (2) F+ and Hfr are synonymous. (3) In F+ cell a bacteriophage carries F factor, while in Hfr cell F factor is an integral part of bacterial chromosome. (4) In F+ cell F factor is in the form of an episome while in Hfr cell, F factor is integrated into the bacterial chromosome.

Difference Between F+ Cell and Hfr Cell in Bacterial Conjugation

23. Conjugation involves transfer of DNA from one cell to another. In E. coli, the cells that cannot transfer their DNA into the recipient cell are (1) Hfr (2) F’ (3) F+ (4) F-

E. coli Conjugation: Cells Unable to Transfer DNA to Recipients

22. In E. coli gal+ and bio+ genes are located very near to each other on genome. A bacterium with F' gal+ on conjugation with F- can lead to diploid condition for (1) gal only (2) bio only (3) gal and bio both (4) E. coli will always remain haploid

E. coli F’ gal+ bio+ Conjugation: Creating Partial Diploids for Closely Linked Genes

21. Under which case of conjugation, recombination for chromosomal genes can be expected in E.coli? (1) F+ X F- (2) F+ X HFr (3) F- X HFr (4) F- X F-

E. coli Conjugation: Chromosomal Recombination in HFr x F- Crosses

20. Bacterial conjugation was first described by Lederberg and Tatum in 1946 as a phenomenon involving the exchange of markers between closely related strains Of Escherichia coli. For experiment they used (1) One auxotroph and one prototroph (2) Two auxotroph and two prototroph (3) Two auxotrophs (4) Two prototroph

The Lederberg and Tatum Experiment

19. The F+ segment of bacterta may be transferred to F bacteria by the process of (1) Conjugation (2) Transduction (3) Transformation (4) Fragmentation

F+ Segment Transfer in Bacteria

18. If bacteria possess two copies of certain genes then they referred as (1) Amphidiploid (2) Merodiploid (3) Euploid (4) Polyploid

Understanding Merodiploidy

17. F-Plasmids in bacteria helps in- (1) Transformation (2) Transduction (3) Conjugation (4) Replication

F-Plasmids in Bacteria

16. Which of the following mattings between E. coli strains would result in a high frequency of transfer of chromosomal genes? (1) F+ X F- (2) F+ X F+ (3) Hfr x Hfr (4) Hfr X F-

E. coli Hfr x F- Mating

15. Five bacterial markers were followed for a co- transduction experiment. The following table documents the observations of this experiment. '+’ denotes co- transduction and '-' denotes lack thereof; 'ND' stands for not determined. Pick the correct order in which the genes are arranged on the bacterial chromosome (1) str-gal-leu-arg-met (2) leu-met-arg-str-gal (3) leu-str-met-gal-arg (4) arg-gal-str-leu-met

Bacterial Co‑transduction Mapping

14. Phages are collected from an infected E. coli donor strain of genotype cys+ Leu+ thr+ and used to transduce a recipient of genotype cys- Leu- thn-, The treated recipient population is plated on a minimal medium supplemented with leucine and threonine. Many colonies grew. Which one of the following combination of genotypes are appropriate for the colonies that grew? (1) cys+ leu+ thr+, cys+ leu- thr+, cys- leu+ thr- (2) cys- leu+ thr+, cys+ leu-thr-, cys+leu+ thr- (3) cys- leu-the-, cys- leu- thr+, cys- leu+ thr- (4) cys+ leu- the-, cys+ leu- thr+, cys+ leu+ thr-

Phage Transduction in E. coli

13. 22 TRANSDUCTION WAS USED TO MAP THE fadL and two linked markers, purF and aroC are shown below. Which one of the following is the correct map for the three genes?

P1 Transduction Gene Mapping of fadL, purF and aroC

12. A co-transduction experiment was performed to decipher the linear order of 4 genes: a, b, c and d. Three sets of experiments were done where transductants were selected for a (Set-1) or b (Set-2) or c (Set-3) and screened for co-transduction of the other markers. SET-1 Selected for Co-transduction Frequency a b 31 a c 3 a d 89 SET-2 Selected for Co-transduction Frequency b a 22 b c 78 b d 68 SET-3 Selected for Co-transduction Frequency c a 0 c b 69 c d 43 Based on the frequencies shown above, identify the most likely order in the genome. (1) a b c d (2) b c d a (3) c d a b (4) a d b c

Gene Mapping by Co‑transduction

11. In a transduction experiment using genotype as a donor and a+b+c+ as a donor and a-b-c- as the recipient, a+ transductants were selected and screened for b and c. The data obtained are shown below. Genotype No. of Recombinant a+b-c- 573 a+b+c- 98 a+b-c+ 11 a+b+c+ 68 The co-transduction frequencies for a+b+ and b+c+, respectively, are: (1) 17% and 12% (2) 22% and 9% (3) 22% and 17% (4) 17% and 9%

Cotransduction Frequency Problem

10. What is prophage (1) λ phage DNA (2) Stage of cell cycle (3) DNA of temperate phage inserted into host chromosome (4) A transposons

What is Prophage?

9. Transduction has been used extensively for genome mapping for bacteria. Which of the following process is useful for gene mapping? (1) Generalized transduction (2) Specialized transduction (3) Site specific recombination (4) Bacterial lysis

Generalized Transduction: Key Process for Bacterial Gene Mapping

8. λ-phage insert their DNA into bacterial host. The site for recombination on host is termed as- (1) attp (2) attB (3) Xis (4) Int

λ-Phage attB Site

7. An experiment was designed to find out the relation between DNA uptake and transformation efficiency. 32P- labelled genomic DNA from Bacillus subtilis (A) and cold genomic DNA from Clostridium Jejeuni (B) mixed in various proportions was used to transform Bacillus subtilis. The results obtained are tabulated below Set No Concentration of DNA used (μg/ml) A B Uptake of 32P labeled DNA (%) Transforming efficiency (CFU) 1 1 1 90 30 2 1 10 82 10 3 1 100 15 5 4 1 1000 5 1 The following interpretations (A to D) could be made A) The transformation is dependent on recombination between homologous sequences. B) Cells did not distinguish between homologous or heterologous sequences for uptake of DNA. C) DNA uptake is based on specific receptors D) DNA degradation dictates transformation efficiency Which of the following interpretations are correct? (1) A and B (2) A and C (3) c and D (4) A and D

 DNA Uptake and Transformation Efficiency in Bacillus subtilis

6. In a transformation experiment, donor DNA from an E. coli strain with the genotypes was used to transform a strain of genotype Z+Y+. The frequencies of transformed classes were: Z+ Y+ 200 Z+ Y- 400 Z- Y+ 400 Total 1000 What is the frequency (%) with which Y locus is co- transformed with the Z locus? (1) 1 (2) 20 (3) 33.3 (4) 40

E. coli Transformation

4. DNA was isolated from a strain of bacterium with genotype a+b+c+d+e+ and transformed into a bacterial strain a-b-c-d-e-. The transformants were tested for the presence of the donated genes. The co-transformed genes were found as follows: a+ and b+ ; c+ and e+ ; d+ and c+ ; b+ and d+ ; What is the order of genes on the bacterial chromosome? (1) a b c d e (2) a c b e d (3) a b c e d (4) a b d c e

Determining Bacterial Gene Order via Cotransformation in Transformation Experiments

5. DNA from a bacterial strain with genotype at b+c+d+e+f+ was isolated and used to transform a strain of bacteria with genotype a-b-c-d-e-f-.The transformed cells were tested for the presence of co-transformed genes and the following types of co-transformants were observed: a+ and c+ e+ and d+ d+ and b+ b+ and f+ c+ and e+ The correct order of genes will be: (1) a b c d e f (2) a c e b f d (3) a c e d b f (4) a b f e d c

Determining Bacterial Gene Order via Cotransformation in Transformation Experiments

3. DNA from a strain of bacteria with genotype a+b+c+d+e+ was isolated and used to transform a strain of bacteria that was a-b-c-d-e-. The transformed cells were tested for the presence of donated genes, The following genes are found be co-transformed i. a+ and d+ ii. b+ and e+ iii. c+ and d + iv. c+ and e+ The order of genes on the bacterial chromosome is (1) a-b-c-d-e (2) a-d-c-e-b (3) a-c-d-e-b (4) a-d-b-e-c

Bacterial Gene Order via Cotransformation Mapping

2. A lac- culture of E. coli was mutagenised. On what media would one spread the mutagenised cells to select for lac+ cells? (1) Minimal media+ lactose. (2) Rich media + lactose. (3) Minimal media + glycerol+ IPTG + X-Gal (4) Rich media+ IPTG + X-Gal

Selecting lac+ E. coli Mutants

1. E. coli cells were transformed with plasmid carrying tetracycline resistance gene and later on plated on LB medium and various colonies were observed but same number of colonies were observed for control non transformed E. coli cells. The probable reason is (1) No transformation has occurred (2) Bacteria are plated just after heat shock and incubation with plasmid (3) E. coli cells were already resistance to tetracycline (4) Wrong plasmid was used

Why Same Number of Colonies in E. coli Tetracycline Transformation on LB Medium?

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