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Genetics Exam 2 - Chapter 6

Terms in this set (43)

Eukaryotic recombination
Typically involves reciprocal exchange of DNA between chromosomes; genetic information is transferred and results in an altered genotype
Prokaryotic recombination
Typically involves replacement of DNA in one cell with DNA from a genetically distinct cell
Vertical transfer
The transfer of DNA between members of same species
Horizontal transfer
The transfer of DNA between members of different species
Minimal medium
Has only a carbon source (glucose) and minerals; organisms that can grow on this are called prototrophs
Prototrophs
Grow on minimal mediums; have genes for producing all amino acids, vitamins, lipids, etc. from the minimal medium
Auxotrophs
Cannot grow on minimal medium alone; minimal medium must be supplemented; complete medium could be used
Complete medium
Have vitamins, amino acids, lipids, etc.
Dilution plating
Make a serial dilution of a bacterial culture; spread ,1 ml of each dilution onto a plate of nutrient agar; incubate the plate for 18 hours; choose the plate with the smallest number of colonies; count the colonies; calculate the number of colonies in the undiluted culture from the number of counted colonies and the dilution factors
F+
Posses an F factor; can lose the F factor to become F- cells; serves as a donor of parts of their chromosomes
F-
Always become F+ cells after conjugation because they receive the F factor; recipient bacteria; receive the donor chromosome material (now known to be DNA) and recombine it with part of their own chromosome
F factor
A circular DNA molecule, with about 100000 basepairs; has many genes, most involved with the transfer of DNA and formation of the f-pilus
F-pilus
A tube like structure required for conjugation; mediate cell-to-cell contact needed for conjugation
Hfr bacteria
Recombination rates are very low during conjugation; F factor transfer is very high; F+; do not turn F- recipient cells into F+ donor cells; cannot donate all genes to recipient cells; different strains can donate different genes
Adaptation hypothesis
Implies that the interaction of the phage and the bacterium is essential to the acquisition of immunity; exposure to the phasge 'induces' resistance in the bacteria
Spontaneous mutations
Occur regardless of the presence or absence of bacteriophage T1
Selection
Refers to culturing the organism under conditions where only the desired mutant grows well, while the wild type does not grow; mutations for almost any desired characteristic can be isolated using this
Minimal medium
To grow on this medium, a bacterium must be able to synthesize all essential organic compounds (prototroph)
Auxotroph
Bacterium has lost, through mutation, the ability to synthesize one or more organic compounds
Genetic recombination
Refers to the replacement of one or more genes present in the chromosome of one cell with those from the chromosome of a genetically distinct cell
Conjugation
A process by which genetic information from one bacterium is transferred to and recombined with that of another bacterium
RecA protein
Plays an important role in recombination involving either a single-stranded DNA molecule or the linear end of a double-stranded DNA molecule that has unwound
Single-strong displacement
A common form of recombination in many bacterial species; when double-stranded DNA enters a recipient cell, one strand is often degraded, leaving the complementary strand as the only source of recombination; this strand must find its homologous region along the host chromosome, and once it does, RecA facilitates recombination
RecBCD protein
An enzyme consisting of polypeptide subunits encoded by three other rec genes; this protein is important when double-stranded DNA serves as the source of genetic recombination
Plasmids
Often exist in multiple copies in the cytoplasm; each may contain one or more genes and often quite a few; their replication depends on the same enzymes that replicate the chromosome of the host cell; are distributed to daughter cells along with the host chromosome during cell division
Episomes
Some plasmids, such as the F factor, can integrate into the host chromosomes; those plasmids that can exist autonomously or can integrate into the chromosome are called _____
R plasmids
Consist of two components - the resistance transfer factora nd one or more r-determinants
RTF
Encodes genetic information essential to transferring the plasmid between bacteria
R-determinants
Genes conferring resistance to antibiotics or heavy metals such as mercury
Col plasmid
Clearly distinct from R plasmids; encodes one or more proteins that are highly toxic to bacterial strains that do not harbor the same plasmid
Colicins
Can kill neighboring bacteria, and bacteria that carry the plasmid are said to be coli-cinogenic
Bacteriophages
Viruses that have bacteria as their hosts
Lysis
The step during infection (phages); completes the lytic cycle
Plaque
A clear area that occurs wherever a single virus initially infected one bacterium in the culture that has grown up during incubation (phages)
Lysogeny
Upon entry of the virus into a bacterial cell, the viral DNA is integrated into the bacterial chromosome instead of replicating in the bacterial cytoplasm
Prophage
The viral DNA integrated into the bacterial chromosome
Temperate phages
Viruses that can either lyse the cell or behaves as a prophage
Virulent phages
Viruses that can only lyse the cell
Lysogenized
A bacterium harboring a prophage has been _____
Transduction
Bacterial recombination mediated by bacteriophages
Specialized transduction
Occurs when transfer of bacterial DNA is not random, but instead, only strain-specific genes are transduced
Generalized transduction
Characterized by the random nature of DNA fragments and genes that are transduced
Cotransduction
Two genes that are close to one another along the bacterial chromosome (i.e., are linked) can be transduced simultaneously
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