Genetics Chapter 6 HW

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Genetics Chapter 6 HW

Name two forms of recombination in bacteria

conjugation and transduction

Bacteriophages have two different types of life cycle; they are

lytic and lysogenic

A bacteriophage that is capable of entering either a lytic or lysogenic cycle is called....

temperate phage

Transduction is a form of recombination in bacteria that involves

bacteriophages

The clearing made by bacteriophages in a lawn of bacteria on an agar plate is called...

plaque

Name the general category into which circular/extrachromosomal dsDNA such as F factors, and Col factor would fall

plasmid

a trp - auxotroph can grow on

Complete Medium and Minimal medium plus amino acids

T/F

In a bacterial cross where the donor (Hfr) is a +b+ and the recipient (F-) cell is a-b-; it is expected that recombinant bacteria will all be a+b+.

False

T/F

Cotransduction of genes is an indication that the genes are linked

True

T/F

To produce recombinants in bacteria, one crossover is better than two.

False

T/F

A plaque is a substance that causes lysis of bacteria.

False

T/F

Lysogeny is most likely associated with transduction.

True

T/F

R plasmids often contain genes for antibody production

False

T/F

The 'interrupted mating technique' provides for a genetic map in Drosophila.

False

Compare and contrast bacteriophage lysis and lysogeny.

Both lysis and lysogeny involve bacterial/phage interactions related to the production of phage progeny. Lysis is where progeny phage burst from the bacterial cell, while lysogeny involves the incorporation of the phage chromosome into the bacterial chromosome.

Why is generalized transduction able to transfer any gene, but specialized transduction is limited to a small set?

Generalized transduction occurs with lytic phages that enter a bacterial cell, fragment the bacterial chromosome and then package some of the bacterial genome with the viral parts. Therefore, any bacterial gene can be included within the newly formed virus. in contrast, specialized transduction occurs with improper excision of viral DNA from the host chromosome in lysogenic phages. Because the integration site is fixed, only those bacterial genes very close to the viral gene can be transferred.

Explain how transduction and transformation can be used to map genes. How are these methods similar and how are they different?

In transformation, the relative frequency at which genes are transferred or cotransformed indicates the distance between the two genes. Closer gene pairs are cotransformed more frequently. Physical contact between two cells is not necessary. Recipient cells take up DNA from the environment directly.


In transduction, a viral vector is neeeded for the transfer of DNA. DNA from the donor cell is packaged into a viral protein coat. The virus containing the bacterial DNA then infects other bacteria, it transfers the bacterial DNA to them. Only genes that are close together are cotransduced. Therefore, the rate of cotransduction give an indication of the physical distance between the two genes.

Explain what is meant by heteroduplex in the context of bacterial transformation.

If transforming DNa is derived from a genetically distinct bacterium, incoming DNA may be different from the host DNA. During initial stages of integration into the bacterial chromosome, the recombinant region contains one DNA that may have a different base sequence than the other strand. Because these strands are not genetically identical (complementary), this double-stranded region is called a heteroduplex.

A geneticist isolates two mutations in bacteriophage. one causes clear plaques (c), other causes minute plaques (m). Previous mapping experiments have shown that the genes responsible for these two mutations are 8 map units apart. he mixes phages with genotype c+m+ and c-m- and uses the mixture to infect bacterial cells. He collects the progeny cells and cultures them on a lawn of bacteria; and observes 1000 plaques. What numbers of the different types of plaques (c+m+, c-m-, c+m-, c-m+) should he expect to see?

1) Plaque phenotype produced by c+m+, 460; by c-m-, 460; by c+m-, 40 and by c+m-, 40.

Explanation: The last two types are recombinants. The distance between recombinants is 8mu or the RF is 8%. 8% of 1000 is 80. Therefore, the two recombinants are each 40.

1000 -80 = 920/ 2 = 460

Assume that one counted 67 plaques on a bacterial plate where 0.1 ml of a 10^-5 dilution of phage was added to bacterial culture. What is the initial concentration of the undiluted phage?

67 X 10 5 X 10 = 6.7 X 10 7 pfu/ ml ( pfu: plaque forming units)

A microbial geneticist isolates a new mutation in E.coli and wants to map its chromosomal location. She uses interrupted-mating experiments with Hfr strains and generalized transduction with the phage. Explain why each technique by itself is insufficient for accurate mapping.

While the interrupted mating experiments will yield the gene order, it will be relative only to fairly distant genes. Thus, the precise location can not be pin pointed. Generalized transduction will yield information with regard to very close markers, which makes it a poor choice for a massive screening experiment. Together, they would be good. Interrupted mating would localize a mutant and generalized transduction can be next used for precise determination of the location within the general region.

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