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) An Hfr strain (arg+, bio+, leu+) is mated to an F- strain (arg-, bio-, leu-). Assume that this Hfr strain transfers arg+ last. You grow the exconjugants on arg- media, supplemented with leu+ and bio+. You recover 423 arg+ exconjugants. These are tested individually for bio and leu and you find the following distribution of genotypes:

arg+, bio+, leu+ 360

arg+, bio+, leu- 9

arg+, bio-, leu+

0 arg+, bio-, leu- 54

a) What is the gene order (show your reasoning)? b) What are the frequencies of recombination between each pair of genes?

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Nestor Rutherford
Nestor RutherfordLv2
29 Sep 2019

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Related questions

Transducing phage can be used to map bacterial genes. Phages are collected from an E. coli donor strain of genotype cys+leu+thr+ and used to transduce a recipient strain of genotype cys-leu-thr-. Initially the treated recipient population is plated on a minimal medium supplemented with leucine and threonine. Many colonies are obtained.

a. What are the possible genotypes of these colonies?

These colonies are then replica plated onto three different media: 1) minimal plus threonine only. 2) minimal plus leucine only, and 3) minimal. What genotypes could, in theory, grow on these three media?

Of the original colonies, 56% are observed to grow on medium 1, 5% on medium 2, and no colonies on medium 3. What are the actual genotypes of the colonies on media 1, 2, and 3?

Draw a map showing the order of the three genes and which of the outer genes is closer to the middle gene.

Hfr Mapping Problem

An Hfr E. coli contains the following genetic traits: kans, lac+ , his+ , trp+ , ampr . It is mated with a recipient E. coli that contains the opposite genetic traits for those traits listed abov: kanr. lac- , his- , trp- , amps . Assume all other catabolic and biosynthetic genes are present in both strains. Note that kanS means the absence of the kanamycin resistance gene in the Hfr strain, which will allow growth only of the recipient cells in the presence of kanamycin. This is necessary to select against the Hfr donor strain as you are monitoring which genes transferred to the recipient.

At periodic intervals, conjugation is disrupted and cells are plated onto several types of defined media. Nothing grows at the beginning of the experiment on media containing lactose, kanamycin, and ampicillin as this is the most selective medium, but all cells grow on complex media containing no ampicillin (the least selective medium). Mating is interrupted at the times listed below and the following are some of your observations of growth characteristics on a few of the selective media plates containing the indicated nutrients/antibiotics:

15 min.

Growth on defined media containing: kanamycin, glucose, histidine (does not contain tryptophan).

No growth on defined media containing: kanamycin, lactose (sole carbon source), tryptophan, histidine.

30 min.

Growth on defined media containing: kanamycin, lactose (sole carbon source), histidine (does not contain tryptophan).

No growth on defined media containing: kanamycin, glucose, tryptophan (does not contain histidine).

No growth on defined media containing: kanamycin, ampicillin, lactose (sole carbon source), histidine, tryptophan.

45 min.

Growth on defined media containing: kanamycin, lactose (sole carbon source) (does not contain histidine or tryptophan).

No growth on defined media containing: kanamycin, ampicillin, lactose (sole carbon source), histidine (does not contain tryptophan).

60 min.

Growth on defined media containing: kanamycin, lactose (sole carbon source) (does not contain histidine or tryptophan).

No growth on defined media containing : kanamycin, ampicillin, lactose (sole carbon source) (does not contain histidine or tryptophan).

1. A cross is made between an Hfr that is met+ thi+ pur+ and an F- that is met- thi- pur-. Interrupted mating studies show that the met+ enters the recipient last, and so met+ recombinants are selected on a medium. The recombinants are tested for the presence of thi+and pur+ alleles. The following numbers of individuals are found for each genotype:

met+ thi+ pur+ 280

met+ thi+ pur- 0

met+ thi- pur+ 6

met+ thi- pur- 52

a. What media are used to detect the four genotypes above? (Use the notation MM for minimal medium.) (10 points (2.5 each))

Genotype

Medium

met+ thi+ pur+

met+ thi+ pur-

met+ thi- pur+

met+ thi- pur-

b. What are the gene order and map distances for these three genes? (15 points.)

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