Cell Cycle, Mitosis, Meiosis, Cytogenetics, and Microbial Genetics

Comprehensive vocabulary flashcards covering the eukaryotic cell cycle, mitosis, meiosis, cytogenetics, eukaryotic and prokaryotic life cycles, viral reproduction, and bacterial genetics.

Cell cycle

The regular sequence of growth and division through which eukaryotic cells replicate themselves, encompassing interphase ($G_1$, $S$, and $G_2$) and the $M$ phase.

$G_1$ and $G_2$ phases

Two gap phases in the eukaryotic cell cycle where the "G" stands for growth; periods during which the cell grows and enlarges prior to division.

$S$ phase

The synthesis phase of the cell cycle during which cellular DNA is completely replicated and synthesized.

Cytokinesis

The physical division of the cytoplasm into two daughter cells, which is distinct from mitosis and serves as the final step of the cell cycle.

Cyclins

Regulatory proteins whose concentrations fluctuate up and down throughout specific stages of the cell cycle to control cell cycle progression.

Cyclin-dependent kinases (CDKs)

Enzymes that phosphorylate target proteins to push the cell cycle forward or hold it back; they are only catalytically active when bound to a specific cyclin.

Cell cycle checkpoints

Specific points in time during the cell cycle (such as $G_1$, $G_2$, and metaphase) where internal and external conditions are verified before allowing the cell to advance.

Sister chromatids

Two identical copies of a chromosome produced during $S$ phase that remain physically connected to one another and are together counted as a single chromosome.

Centromere

A specific region of chromosomal DNA, often located near the middle, where sister chromatids are held together and where the kinetochore forms.

Kinetochore

A multi-protein complex assembled upon the centromeric DNA that helps hold sister chromatids together and provides an attachment site for spindle microtubules.

Mitotic spindle

A dynamic cytoskeletal apparatus composed of microtubule fibers projecting from opposite cell poles that coordinates chromosome alignment and segregation during mitosis.

Astral microtubules

Microtubules radiating outward from the centrosome near the cell cortex that serve as anchors to stabilize the spindle poles within the cell.

Polar microtubules

Microtubules projecting from each spindle pole toward the cell center that overlap and interact with microtubules from the opposite pole to push the poles apart.

Kinetochore microtubules

Microtubules that physically extend from the spindle poles and attach directly to the kinetochore protein complexes of chromosomes.

Centrosome

The microtubule-organizing center located at each pole of an animal cell responsible for nucleating and organizing the mitotic spindle.

Centrioles

A pair of barrel-like, churro-shaped microtubule structures oriented at a $90^\circ$ angle inside animal centrosomes; they are absent in plant cells.

Prophase (mitosis)

The initial phase of mitosis characterized by the condensation of chromatin into visible sister chromatids and the initial formation of the mitotic spindle.

Prometaphase (mitosis)

The stage of mitosis where the nuclear envelope fully breaks down, spindle poles move apart, and kinetochore microtubules attach to kinetochores.

Metaphase (mitosis)

The stage of mitosis in which all chromosomes align along the equator or metaphase plate in the center of the cell.

Anaphase (mitosis)

The stage of mitosis where the physical connection between sister chromatids breaks, and individual chromosomes are pulled toward opposite spindle poles.

Telophase (mitosis)

The concluding stage of mitosis during which the nuclear envelope reforms around each separated set of chromosomes at the cell poles.

Cleavage furrow

A contractile ring composed of actin filaments that constricts like a drawstring to divide animal cells during cytokinesis.

Cell plate

A rigid partition that forms between dividing plant daughter cells by synthesizing a new cell wall to complete cytokinesis.

Meiosis

A specialized two-step nuclear division process in sexually reproducing organisms that reduces the chromosome number by half to generate haploid gametes.

Homologous chromosomes (homologs)

Pairs of chromosomes (one maternal and one paternal) that carry the same genes at the same loci, though they may carry different versions of those genes.

Crossing over

A genetic recombination event occurring in prophase I of meiosis where segments of non-sister chromatids are exchanged between homologous chromosomes.

Bivalent (Tetrad)

A homologous chromosome pair aligned side-by-side during prophase I and metaphase I of meiosis, consisting of four sister chromatids.

Synaptonemal complex

A proteinaceous zipper-like structure that temporarily glues homologous chromosomes together along their length to allow crossing over during meiosis I.

Chiasma (plural: Chiasmata)

The visible X-shaped cytological junction that persists where crossing over and genetic exchange took place between non-sister chromatids.

Haploid ($n$)

A cell condition characterized by having only one single complete set of chromosomes, typical of gametes resulting from meiosis.

Diploid ($2n$)

A cell condition characterized by having two complete sets of chromosomes—one maternal set and one paternal set.

Diploid-dominant life cycle

A sexual life cycle typical of animals where the multicellular adult body is diploid ($2n$) and the haploid ($n$) phase is restricted to unicellular gametes.

Gametogenesis

The biological process of cellular differentiation that transforms cells into mature functional gametes (sperm or egg cells), distinct from meiosis.

Haploid-dominant life cycle

A sexual life cycle found in most fungi where the main multicellular organism is haploid ($n$), and the diploid ($2n$) stage is restricted to a brief zygote that promptly undergoes meiosis.

Alternation of generations

A plant and algal life cycle that alternates between a multicellular diploid ($2n$) sporophyte generation and a multicellular haploid ($n$) gametophyte generation.

Sporophyte

The multicellular diploid ($2n$) generation in plants that undergoes meiosis to produce haploid spores.

Gametophyte

The multicellular haploid ($n$) generation in plants that produces eggs and sperm via mitosis.

Karyotyping

A laboratory procedure that arranges and visualizes stained chromosomes from an individual to analyze their number, size, banding patterns, and structure.

$p$ arm and $q$ arm

The standard designations for the arms of a chromosome on opposite sides of the centromere, where $p$ denotes the short arm and $q$ denotes the long arm.

Metacentric chromosome

A chromosome whose centromere is positioned centrally, dividing it into arms of approximately equal length.

Submetacentric chromosome

A chromosome whose centromere is positioned slightly off-center, creating a distinctly shorter $p$ arm and longer $q$ arm.

Acrocentric chromosome

A chromosome whose centromere is located very close to one end, leaving an extremely short $p$ arm.

Telocentric chromosome

A chromosome whose centromere is positioned directly at the terminal end of the chromosome.

Euploid

An individual or cell that carries the standard, exact multiple of the complete chromosomal set for that species.

Polyploid

An organism possessing three or more complete sets of chromosomes; highly prevalent and well-tolerated in plants but abnormal in animals.

Aneuploidy

An abnormal condition in which an individual has an incomplete chromosome set due to one extra or one missing individual chromosome (such as trisomy 21).

Nondisjunction

An error in chromosome segregation during meiosis I or meiosis II where homologs or sister chromatids fail to separate, producing gametes with abnormal chromosome numbers.

Capsid

The protective external protein coat that encloses and protects the viral genetic material inside a virion.

Bacteriophage

A specialized virus that specifically targets and infects bacterial cells, often exhibiting a complex lunar-lander-like structure like the T4 phage.

Lytic cycle

A viral reproductive pathway where the virus commandeers the host cell, synthesizes viral genomes and proteins, and causes the host cell to burst (lyse) to release progeny virions.

Lysogenic cycle

A viral pathway where viral DNA inserts into the host bacterial genome as a dormant prophage, replicating passively alongside host division until environmental signals trigger lysis.

Nucleoid

The distinct, non-membrane-bound cytoplasmic region within a prokaryotic cell where the single circular bacterial chromosome is organized.

Plasmids

Small, circular, extrachromosomal DNA molecules in bacteria that replicate independently of the main chromosome and often carry adaptive genes such as antibiotic resistance.

Binary fission

The simplified asexual division process utilized by bacteria in which a cell copies its circular chromosome and divides down the middle into two daughter cells.

Bacterial colony

A visible mass or mound of bacterial cells growing on solid agar, all of which originated via clonal division from a single initial progenitor cell.

Horizontal gene transfer

The movement of genetic material between distinct, non-parent-to-offspring organisms, occurring in bacteria via conjugation, transformation, or transduction.

Conjugation

Direct transfer of plasmid DNA between two bacterial cells via a physical mating bridge called a sex pilus.

Transformation

A genetic transfer process in which a competent bacterial cell binds and internalizes free fragments of foreign DNA released from dead bacteria in its environment.

Transduction

Viral-mediated horizontal gene transfer occurring when a bacteriophage accidentally packages a piece of host bacterial DNA and delivers it into a newly infected bacterium.

Antibiotics

Chemical substances (typically antibacterial molecules) that kill bacteria or halt their essential processes—such as cell wall or protein synthesis—without harming the host organism.