Dictionary > Fluctuation test

Fluctuation test

Fluctuation test
(Science: investigation) test devised by Luria and Delbruck to determine whether genetic variation in a bacterial population arises spontaneously or adaptively. in the original version the statistical variance in the number of bacteriophage resistant cells in separate cultures of bacteriophage sensitive cells was compared with variance in replicate samples from bulk culture. The greater variance in the isolated populations indicates that mutation occurs spontaneously before challenge with phage. (The proportion of resistant cells depends upon when after isolation the mutation arises which will be very different in separate populations).
The fluctuation test shows that mutations occur randomly in a growing culture, and are not induced by the selection agent. The fluctuation test shows that mutations occur randomly in a growing culture, and are not induced by the selection agent. If mutations were induced, for example by streptomycin on the plates, all the plates would have approximately the same number of colonies. In contrast, if mutations occured randomly in the growing population, when the culture was subdivided some tubes contained a population of cells in which the mutation occurred early in the growth period, whereas in others it may have occurred late, or not at all. There will be many more colonies on the plate if the mutation arouse early during growth than if the mutation arouse late in the growth period because the mutants would have undergone more rounds of replication in the former case.If mutations were induced, for example by streptomycin on the plates, all the plates would have approximately the same number of colonies. In contrast, if mutations occured randomly in the growing population, when the culture was subdivided some tubes contained a population of cells in which the mutation occurred early in the growth period, whereas in others it may have occurred late, or not at all. There will be many more colonies on the plate if the mutation arouse early during growth than if the mutation arouse late in the growth period because the mutants would have undergone more rounds of replication in the former case.


You will also like...

Neurology of Illusions
Neurology of Illusions

Illusions are the perceptions and sensory data obtained from situations in which human error prevents us from seeing the..

Genetics – Lesson Outline & Worksheets
Genetics – Lesson Outline & Worksheets

  Topics Modules Quizzes/Worksheets Description Introduction to Genetics Genetics – Definition: Heredity and ..

New Zealand Fauna
New Zealand’s Unique Fauna

Meet some of New Zealand's unique fauna, including endemic insects, frogs, reptiles, birds, and mammals, and investigate..

Still freshwater and plants
Still Freshwater & Plants

Plants in lentic habitats have features not found in terrestrial plants. They acquired these features as they adapt to t..

Cambial cells
Plant Tissues

Plant organs are comprised of tissues working together for a common function. The different types of plant tissues are m..

DNA carries genes coding for proteins
Genetic Information and Protein Synthesis

Genes are expressed through the process of protein synthesis. This elaborate tutorial provides an in-depth review of the..