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Genome
All the genes present in a cell or virus
- prokaryote usually have on set (haploid)
- Eukaryote usually have two sets (diploid)
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Genotype
The specific set of genes an organism possesses
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Phenotype
The collection of characteristics of an organisms that can be observed
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Vertical transmission
transmission of genetic information from parent to offspring
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Horizontal transmission
genetic information transferred from one cell to another cell
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Conclusion from experiment of Avery, MacLeod, and McCarty (mice)
The molecule that carries the heritable information is DNA.
DNA is the genetic material
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The E. Coli chromosome has been mapped using conjugation, transduction, moleculary cloning, and sequencing.
E. Coli has been a useful model organism, and a considerabl amount of information has been obtained from it, not only about gene structure but also gene function and regulation
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Plasmids are small circular or linear DNA molcules that carry nonessential genes. Although a cell can contain more than one plasmid, these cannont be closely related genetically.
Although they have no extracellular form, plasmids can be transferred by the process of conjugation.
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Mutation is a heritable change in DNA sequence that can lead to a change in pheotype. Selectable mutations are those that give the mutant a growth advantage under certain environmental conditions and are espeically useful in genetic research.
If selection is not possible, mutants must be identified by screening.
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Mutation, which can be either spontaneous or induced, arise because of changes in the base sequence of the nucleic acid of an organism's genome. A point mutation, which is due to a change in a single base pair, can lead to a single amino acid change in a polypeptide or to no change at all, depending on the codon.
In a nonsense mutation, the codon becomes a stop condon amd an incomplete polypeptide is made. Deletions and isertions cause more dramatic changes in the DNA, including frameshift mutations that often result in complete loss of gene function.
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Different types of mutations occur at different frequencies. For a typical bacterium, mutation rates on 10-6 to 10-9 per kilobase pair are generally seen.
Although RNA and DNA polymerase make errors at about the same rate, RNA genomes typically accumulate mutations at much higher frequencies than DNA genomes.
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Mutagens are chemical, physical, or biological agents that increase mutation rate. Mutagens can alter DNA in many different ways.
However, alterations in DNA are not mutations unless they are inherited. Some DNA damage can lead to cell death if not repaired, and both error-prone and high-fidelity DNA repair systems exist.
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The Ames test employs a sensitive bacterial assay system for decting chemical mutagens in the environment.
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Homologous recombination arise when closely related DNA sequences from two distinct genetic elements are combined together in a single element.
Recombinatin is an important evolutionary process, and cells have specific mechanisms for ensuring that recombination takes place.
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Certain prokaryotes exhib competence, a state in which cells are able to take up free DNA released by other bacteria. Incorporation of donor DNA into a recipient cell requires the activity of single-stranded binding portein, RecA proteins and sereral other enzymes.
Only competent cells are tranformable.
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Transduction is the tranfer of host genes from one bacterium to another by a bacterial virus. In generalized transduction, defective virus particles randomly incorporate fragments of the cell's chromosomal DNA, but the transducing efficiency is low.
In specialized transduction, the DNA of a temperate virus excises incorrctly and takes adjacent host genes along with it; the transducing efficiency here may be very high.
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Conjugation is a mechanism of DNA tranfer in prokaryotes that reuqires cell-to-cell contact. Conjugation is controlled by genes carried by certain plasmids (such as the F plasmid) and involves transfer of the plasmid from a donor cell to a recipient cell.
Plasmid DNA tranfer involves replication via the rolling circle mechanism.
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The donor cell chromosome can be mobilized for tranfer to a recipient cell. This requires an F plasmid to integrate into the chromosome to form the Hfr phenotype. Transfer of the host chromosome is rarely complet but can be used to map the order of the genes on the chromosome.
F' plasmids are previously integrated F plasmids that have excised and captured some chromosomal genes.
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Archaea lag behind Bacteria in the development of systems for gene transfer. Many antibiotics are ineffective against Archaea, making it difficult to select recombinants effectively.
Moreover the unusual growth conditions needed by many Archaea make genetic experimentatin difficult. Nevertheless, the genetic tranfer systems of Bacteria - transformation, transduction, and conjugation - are all know in Archaea.
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Transposons and insertion sequences are genetic elements that can move from one location on a host DNA molecule to another by transposition, a type of site-specific recombination.
Transposition can be either replicative or conservative. Transposons often carry genes encoding antibiotic resistance and can be used as biological mutagens.
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Auxotroph
an organism that has developed a nutritional requirement, often as a result from mutation
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Cistron
a gene defined as the cis-trans test; a segment of DNA (or RNA) that encodes a single polypeptide chain.
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Conjugation
transfer of genes from one Prokaryote cell to another cell by a mechanism involving cell-to-cell contact.
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Heteroduplex
A DNA double helix composed of single strands from two different DNA molecules.
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Hfr Cell
a cell with the F plasmid integrated into the chromosome
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Induced mutation
a mutation caused by external agent such as mutagenic chemicals or radiation
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Insertion sequence (IS)
The simplest type of transposable element, which carrries only genes involved in transposition.
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Missense mutation
A mutation in which a single codon is altered so that one amino acid in a protein is replaced with a different amino acid
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Mutagen
An agent that causes mutation
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Mutation
A heritable change in the base sequence of the genome of an organism
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Mutator strain
A mutant strain in which the rate of mutation increases
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Nonsense mutation
A mutation in which the codon for an amino acid is changed to stop a codon
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Codon
A sequence of three bases in mRNA that encodes a specific amino acid
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Plasmid
An extrachromosomal genetic element that has no extracellular form
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Point Mutation
A mutation that involves a single base pair
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Recombination
The process by which DNA molecules from two separate sources exchange sections or are brought together into a single DNA molecule
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Regulon
A set of genes or operons that are transcribed separately but are coordinately controlled by the same regulatory protein
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Reversion
Alteration in DNA that reverse the effects of prior mutation
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Operons
One or more genes transcribed into a single RNA and under the control of a single regulatory site.
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Rolling circle Replication
mechaism of replication double-stranded circular DNA that starts by nicking and unrolling one strand and using the other (still circular) strand s a template for DNA synthesis
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Screening
A procedure that permis the indentification of orgnaisms by phenotype or genotype, but does not inhibit or enhance the growth of particular pheno or geno type.
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Selection
placing organisms under conditions where the growth of particular pheno or genotype will be favored or inhibited
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Silent mutation
A change in DNA sequence that has no effect on the phenotype
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Spontaneous mutation
A mutation that happen 'naturally' witout the hlep of mutagenic chemicals or radiation.
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Transduction
Transfer of host cell genes from one cell to another cell by a virus
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Transformation
The transfer of bacterial genes involving free DNA
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Transition
A mutation in which a pyrimidine base is replaced by another pyrimidine
or a purine is replaced by another purine
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Transposable element
A genetic element with the ability to move (transpose) from one site to another on host DNA molecules
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Transposon
A type of transposable element that acarries genes in addition to those involved in transposition
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Transversion
A mutation in which a pyrimidine base is repolaced by a purine or vice versa
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Wild-type strain
A bacterial strain isolated from nature
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