Gene Mapping, Bacterial Genetics, and Viral Life Cycles

Vocabulary practice flashcards covering three-point gene mapping, crossover probabilities, bacterial genetics, horizontal gene transfer, and viral replication cycles based on the lecture.

Single Crossover (SCO)

A genetic recombination event where a single break and exchange occurs between non-sister chromatids, occurring with medium probability relative to double crossovers and non-crossover events.

Double Crossover (DCO)

The rarest recombination event where a chromatid undergoes two breaks and repairs, resulting in the exchange of an internal gene segment between chromosomes.

Rarest Single Mutant Phenotype Rule

The mapping guideline establishing that the gene corresponding to the rarest single mutant phenotype is the gene positioned in the middle of a three-gene sequence on a chromosome.

Map Unit

A measurement of genetic distance representing recombination probability, calculated by multiplying the decimal recombination frequency (the sum of relevant single and double crossover frequencies) by 100.

Prototroph

A wild-type, commonly occurring bacterium capable of growing under typical, standard culture conditions without specialized nutritional requirements.

Auxotroph

A mutant bacterial strain that cannot survive or grow under normal baseline conditions because it requires specific supplemented nutrients or specialized conditions.

Plasmid

A circular extrachromosomal DNA element in bacteria that replicates independently of the main chromosome and carries accessory genes that can aid survival under abnormal conditions.

$F^+$ (F-positive)

A bacterial donor cell carrying the fertility factor plasmid, giving it the ability to transfer plasmid DNA to a recipient cell.

$F^-$ (F-negative)

A recipient bacterial cell that initially lacks the fertility plasmid prior to conjugation.

Horizontal Gene Transfer

The non-reproductive direct transmission of genetic material between living microbial individuals via conjugation, transformation, or transduction.

Conjugation

A form of horizontal gene transfer in bacteria where genetic material is transferred directly from a donor to a recipient cell across a physical cytoplasmic bridge.

Transformation

A horizontal gene transfer mechanism where exogenous fragments of free DNA or plasmids in the environment are taken up and incorporated into a bacterium's genome.

Transduction

The process of horizontal gene transfer in which a bacteriophage virus acts as a vector that carries host DNA fragments from one bacterial cell to another.

Bacteriophage

A specialized category of virus that targets, infects, and replicates within bacterial host cells.

Lysogenic Cycle

A viral life cycle in which the viral genome incorporates directly into the host genome as a dormant prophage and replicates alongside host cell division without killing the host.

Prophage

The dormant, integrated viral DNA sequence inserted into the circular chromosome of a bacterial host during the lysogenic cycle.

Lytic Cycle

An active viral cycle wherein host machinery is commandeered to mass-produce viral components, terminating with the lysis and destruction of the host cell to release mature virions.

Retrovirus

A virus possessing an RNA genome that utilizes reverse transcriptase to synthesize a DNA copy within the host cell before integrating into the host's chromosomal DNA.

Reverse Transcriptase

A viral enzyme packaged by retroviruses that transcribes viral single-stranded RNA into complementary DNA ($\text{cDNA}$) inside a host cell.

Retrotransposon

A repetitive, mobile DNA sequence ('jumping gene') derived from ancestral retroviral infections that replicates and transposes into different genomic sites via an RNA intermediate.

Close Neuburg Virus

A megavirus discovered near Vienna with a genome substantially larger than those of many bacterial species.