Gene Mapping, Chromosome Variation, Bacterial & Viral Genetics, and DNA Structure

Vocabulary flashcards covering key concepts, genetic terms, mechanisms, and structures from Chapters 7, 8, 9, and 10 of GEN3000.

Linked Genes

Genes located close together on the same chromosome that do not undergo independent assortment and tend to segregate together.

Complete Linkage

A state of gene linkage occurring when no crossing over takes place between two genes, resulting in $100\%$ parental or nonrecombinant gametes.

Single Crossovers

Exchange events occurring between two nonsister chromatids used to determine the relative distance between two linked genes.

Double Crossovers

Double exchanges of genetic material between chromatids used to determine both the relative distance and the gene order among three linked genes.

Aneuploidy

A chromosomal variation in which an organism gains or loses one or more individual chromosomes, altering the chromosome number (e.g., $2n + 1$ or $2n - 1$) without changing complete sets.

Monosomy

The loss of a single chromosome from a diploid genome ($2n - 1$), exemplified in humans by Turner's Syndrome ($45,XO$).

Trisomy

The gain of a single extra chromosome in a diploid genome ($2n + 1$), such as Trisomy 21 which causes Down's Syndrome.

Polyploidy

A chromosomal condition in which an organism possesses more than two complete haploid sets of chromosomes (e.g., $3n$, $4n$).

Autopolyploidy

A type of polyploidy where an organism possesses three or more complete chromosome sets derived entirely from the same species.

Allopolyploidy

A type of polyploidy resulting from hybridization between different species, resulting in chromosome sets from multiple species.

Nondisjunction

The failure of paired homologous chromosomes or sister chromatids to disjoin and segregate properly during cell division in meiosis I or meiosis II.

Nullisomy

The loss of both members of a homologous pair of chromosomes from a diploid cell, represented as $2n - 2$.

Tetrasomy

The gain of two extra homologous chromosomes to a diploid genome, represented as $2n + 2$.

Terminal Deletion

A chromosomal mutation characterized by the loss of a segment near one end or tip of a chromosome.

Intercalary Deletion

A chromosomal mutation involving the loss of an interior segment from within the body of a chromosome.

Deletion Loop

An unpaired structure formed during meiotic synapsis when a normal chromosome aligns with a homologous chromosome containing a deletion.

Gene Dosage

The number of copies of a specific gene present within a genome, which directly influences the quantity of gene product produced.

Chromosome Inversion

A chromosomal rearrangement in which a segment of a chromosome is flipped $180^\circ$ relative to its original sequence without losing genetic material.

Robertsonian Translocation

A reciprocal translocation involving breaks at the extreme ends of the short arms of two nonhomologous acrocentric chromosomes, forming a large metacentric chromosome and a small lost fragment.

Genetic Anticipation

A phenomenon where repeat expansion mutations become progressively larger across generations, leading to an earlier age of disease onset and increased clinical severity.

Prototrophs

Wild-type bacterial strains capable of synthesizing all essential organic nutrients and growing on minimal growth medium.

Auxotrophs

Mutant bacterial strains that have lost the capacity to synthesize one or more essential organic compounds and require supplemented medium to grow.

Plasmids

Small, extra-chromosomal, circular double-stranded DNA molecules in bacteria that replicate independently of the main bacterial chromosome.

F Factor

A specific bacterial plasmid that contains genes controlling plasmid replication and regulating genetic transfer during bacterial conjugation.

Colicin Plasmids

Bacterial plasmids derived from E. coli that encode colicins, which are toxic proteins capable of killing non-carrier bacterial strains.

Bacterial Conjugation

The process of genetic exchange in bacteria where DNA is directly transferred from a donor cell to a recipient cell through a sex pilus.

Hfr Strain

A high-frequency recombination strain of bacteria in which the F factor plasmid has integrated directly into the bacterial chromosome.

Bacterial Transformation

A mechanism of gene transfer in which a competent recipient bacterium imports extracellular free DNA fragments from its environment and incorporates them into its chromosome.

Competence

A specialized physiological state of a bacterial cell enabling it to bind and internalize exogenous extracellular DNA.

Cotransformation

The simultaneous uptake and integration of two or more linked genes located on the same extracellular DNA fragment during bacterial transformation.

Plaque Assay

A quantitative laboratory procedure used to count bacteriophages in a culture by measuring clear zones of lysed bacteria called plaques on an agar plate.

Prophage

A bacteriophage genome integrated into the circular bacterial chromosome during the lysogenic cycle.

Temperate Phages

Bacteriophages that are capable of establishing either a lytic cycle leading to host cell destruction or a lysogenic cycle as a prophage.

Bacterial Transduction

The transfer of bacterial genes from a donor bacterium to a recipient bacterium mediated by a bacteriophage vector.

CRISPR-Cas

An adaptive immune mechanism in bacteria that captures foreign viral DNA sequences and uses RNA-guided Cas nucleases to cleave invading bacteriophage genomes.

PAM Motif

A short $2$ to $6$ base pair DNA sequence immediately following a target site that is recognized by Cas proteins to enable targeted cleavage of viral DNA.

Central Dogma

The foundational rule of molecular biology stating that genetic information flows from DNA replication to RNA transcription and protein translation.

Tetranucleotide Hypothesis

An early theory proposed by Phoebus Levene stating that DNA was composed of identical repeating units of four nucleotides, erroneously implying a lack of sequence diversity.

Chargaff's Rules

The empirical findings by Erwin Chargaff establishing that in DNA, adenine equals thymine ($A = T$), guanine equals cytosine ($G = C$), and total purines equal total pyrimidines ($A + G = C + T$).

Nucleoside

A chemical compound consisting of a purine or pyrimidine nitrogenous base linked to a pentose sugar (ribose or deoxyribose).

Nucleotide

The fundamental monomeric unit of nucleic acids, consisting of a nucleoside bonded to one, two, or three phosphate groups.

Phosphodiester Bond

A covalent linkage connecting the $5'$ phosphate group of one nucleotide to the $3'$ hydroxyl ($-OH$) group of an adjacent nucleotide in a nucleic acid chain.

Retroviruses

RNA-containing viruses that utilize the enzyme reverse transcriptase to transcribe their RNA genome into complementary DNA for integration into a host genome.