Hello everyone, I have this homework of molecular biology that i would like your

Question

Hello everyone,

I have this homework of molecular biology that i would like your input.

My answers are the follow for the question written below my answers:

1) strain A and D has the same genotype. if we consider strain A as a wild type, I+O+Z+, where i is Lac I gene responsible for repressing B-gal production, O the operator, and Z the lacZ gene. Lets consider this strain as diploid, so the wild type would be I+O+Z+/ I+OCZ -. Where Oc is a constituative mutant(expressing all the time), and Z - a mutant gene. Eventhough you have the Oc, the mutation wont have any effect on Z, because Z doesnt make a working functional B-gal due to its mutation. If we invert these sequences, I+O+Z - / I+OCZ+ we will still have the same genotype as the wild type, however now Oc will be able to regulate Z, because its functional, producing B-gal constantly. And O+ will regulate the Z mutation, but not being able to produce B-gal. Therefore, even in the presence of Glucose, B-gal still will be synthesize.

I coundnt come up with an plausible answer why strain B and C werent the same phenotype. I would appreciate if i could get the imput from everyone.

2)

a) Both have the same phenotype because both have the characteristic of not being able to synthesize B-gal.

b) No, because not every same phenotype has the same genotype, so the genotype can be different for both strains.

c) yes (i also cant put in words why these 2 have different genotype)

Bacteria need to synthesize -galactosisae (-gal) to survive when they grow on a medium containing lactose as their only source of carbon. When glucose is the only carbon source, growing bacteria do not synthesize -gal. The synthesis of -gal at 22°C and 37°C of 4 strains of bacteria (A, B, C, and D) was tested on solid media containing either glucose or lactose as a source of carbon. The following table summarizes the results of this study.

Strains Solid medium+glucose Solid medium+lactose

22C 37C 22C 37C

A No No Yes Yes

B No No Yes No

C No No No No

D Yes Yes Yes Yes

No: no synthesis of -gal; Yes: synthesis of -gal

The strains in questions 2 & 3 are not the strains described in the table.1) Which strains (A to D) do share the same genotypes? Briefly explain.

2) If two strains growing on solid medium with glucose do not synthesize -gal. a) Do the two strains share an identical phenotype? Briefly explain

b) Would you conclude that the two strains have the same genotype? Briefly explain

3) A strain grows on solid medium with glucose and synthesizes -gal while another does not grow on solid medium with lactose. Are the genotypes of these two strains different? Briefly explain

Thank you so much

Vinny

Explanation / Answer

1.

First I would like say that the question is not clear and it is confusing.

Anyway, If we talk about strains A and D, A strain being wild type, the strain D has a mutation on gene Z and thus when diploids are considered the strains A and D have same genotype with altered expression. The B and C strains cannot be same type of mutants containing same genotype. The mutations in B and C strains can be on different genes such as l or O. Hence, B and C strains are not similar in genotype but phenotype may be same because they cannot synthesize B-gal.

2.

The strains A and D can have same genotype because both strains can synthesize the B-gal at both 220 and 370 C temperatures.

The strains able to synthesize the glucose but cannot synthesize the B- gal share same phenotype with different genotype.

The genotype of the 2 strains cannot be same because the mutation of the two strains cannot be on the same gene.

3.

The strain growing on glucose synthesizes B-gal while the other strain does not grow on solid medium with lactose means cannot synthesize B-gal. Hence, the genotypes of two strains are different because the B-gal encoding gene is mutated in the strain that does not grow on lactose and hence the gene is not functional. Thus, B - gal is not synthesized.

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