2 Introduction to Bacterial Genes

How does Vibrio fischeri iluminate?

During the process of bioluminescence, Vibrio fischeri produces a small burst of light through a biochemical reaction involving luciferase.

What are the types of mutants with altered phenotypes that would help researchers understand Vibrio fischeri?

1. mutants that always produces luminescence

2. mutants that do not luminesce

What coined the term “1 gene, 1 enzyme hypothesis”?

Beadle & Tatum in 1941, however they specifically reffered to an enzyme because that is what were able to directly corrolate.

What are moonlighting proteins?

have the ability to perform two or more completely different and independent biological funcitons.

True or false: a genotype mutation always leads to a phenotype change

False, silent mutations, even missense can lead to unaffected proteins

What is forward/classical genetics?

Finding mutants of interest among many mutants by screening mutants that do or don’t do the process of interest.

Phenotype —→ Genotype

wild type —→ mutants of interest —→ genes of interest —→ funciton

Mutates randomly

What is reverse/modern genetics

Make a specific mutant of interest and observe phenotype by inducing a specific mutation and obersving results.

Genotype —→ Phenotype

wild type —→ genes of interest —→ mutants —→ function

Uses bioinformatics (whole gene needs to be known)

What are advantages of using bacteria for genetic research?

1. bacteria are haploid: one copy/allele for each gene

2. short generation times: facilitates experimentation

3. asexual reproduciton: all prgeny are identical/clonal

4. genetic exchange: allows manipulation of genetic material of an organism

5. Colonies can be grown on agar plates: isolation of cells or clonal populations

6. Can employ selection: allowed for isolation of rare/infrequent mutants

What is the difference between screening and selecting

screening: All tested samples or cells survive. You must inspect, test, or sort through every individual unit to find the ones with the desired trait

selecting: A specific pressure (like a toxin, antibiotic, or extreme temperature) kills off non-functional or unwanted organisms. Only cells with the correct phenotype or resistance survive the process.

Gene

molecular unit of heredity

Allele

variant form of a gene

Genome

complete genetic content of an organism; defines a species; organized into functional units

Genotype

the genetic composition of an organism; the specific allele make up of an organism; the DNA actual sequence of an organisms genome

Phenotype

observable trait

Strain

a member of a species with a unique genotype

Wild type (wt)

an organism whose genetic traits are considered as reference; reference strain of the species

mutant

a strain carrying a mutation

Mutation

a heritable change in the DNA sequence, as compared to the wild type (may not cause a mutation phenotype)

Haploid

Diploid

Merodiploid

Haploid: a cell containing a single set of genes (1 copy/gene)

Diploid: a cell containing two sets of the genome (2 copies/gene)

Merodiploid: a partial diploid; a strain carrying two copies of one or some genes

• homozygous: both alleles are the same lacZ+ lacZ+

• heterozygous: the alleles are different lacZ+ △lacZ

• Dominant allele: lacZ+

• recessive △lacZ::kan