Midterm 3 (Chapters 7 and 8)

Question 1

Plaque

Answer 1

A clear spot in the lawn of bacteria that indicates the cells were lysed.

Question 2

Host range

Answer 2

The strains of bacteria a bacteriophage can bind to and lyse.

Question 3

Wild type plaques versus mutant plaques

Answer 3

The wild type plaques are small with fuzzy margins. The rapid lysis mutants on the other hand create large plaques with sharp margins.

Question 4

Lysis inhibition

Answer 4

When lysis is delayed for up to 2 hours. It doesn’t occur in bacteria infected with the r mutants

Question 5

Host range mutants

Answer 5

The mutants have clear plaques because they can infect and lyse all host cells while the wild type produces turbid plaques because they infect only S cells and not R cells.

Question 6

What did Hershey do in his experiments

Answer 6

He studied phage to phage recombination by infecting host bacteria with two different types of phage and then looking for recombinant phenotypes

Question 7

MOI

Answer 7

Multiplicity of infection. In order to get phages to recombine, he used a high MOI so there were multiple phages per bacteria.

Question 8

Why use serial dilutions?

Answer 8

It is more accurate than using a teeny amount from a pipet and to see clear plaques

Question 9

Why did Benzer choose to work on the rII locus in T4 bacteria?

Answer 9

1) the mutants breed true
2) It’s easy to generate a large number of phages and screen them
3) Easy to screen, there are conditional mutants

Question 10

What does a restrictive condition allow?

Answer 10

Only allows the mutant to grow

Question 11

What does the permissive condition allow?

Answer 11

it allows the wild type to grow

Question 12

What can rII mutants grow on?

Answer 12

They can grow on E. coli B but not on K. The wild type can grow on both

Question 13

How to count number of recombinants

Answer 13

The number of recombinants is 2 x the number present because 1/2 of the recombinants turn into WT

Question 14

Population

Answer 14

A group of interbreeding individuals f the same species that inhabit the same space at the same time.

Question 15

Microevolution

Answer 15

The change in the frequency of alleles within a population, or alterations of a populations gene pool

Question 16

Phenotype frequency

Answer 16

The proportion of individuals in a population that express a particular phenotype

Question 17

Genotype frequency

Answer 17

The proportion of total individuals in a population that carry a particular genotype

Question 18

Allele frequency

Answer 18

The proportion of gene copies in a whole population that are of a given allele type

Question 19

Hardy Weinberg law assumptions (5)

Answer 19

1) The population is large
2) Mating is random
3) No new mutations appear in the gene pool
4) No migration takes place into or out of the population
5) No genotypes have impact on the ability to survive to reproductive age and transmit genes to the next generation

Question 20

Hardy Weinberg equation

Answer 20

p^2 + 2pq +q^2 = 1

Question 21

Genetic drift

Answer 21

A change in allele frequency as a consequence of the randomness of inheritance from one generation to the next

Question 22

Fitness

Answer 22

Defined by population geneticists as an individuals relative ability to survive and transmit it’s genes to the next generation

Question 23

Natural selection

Answer 23

The process in nature that progressively eliminates individuals whose fitness is lower and chooses individuals of higher fitness survive and pass on their genes