Biology: Molecular Genetics, Cell Division, and Patterns of Inheritance

Practice vocabulary flashcards covering molecular biology, DNA structure, transcription, translation, gene regulation, cell division (mitosis and meiosis), and Mendelian and complex inheritance patterns.

Nucleotide

A building block of nucleic acids composed of three distinct components: a phosphate group, a 5-carbon sugar (deoxyribose in DNA or ribose in RNA), and a nitrogenous base.

Antiparallel

The characteristic spatial orientation of the two complementary strands in a DNA molecule, where they run parallel to each other but in opposite directions.

Genome

All the genetic material contained within the cells of an organism.

Gene

A small region or portion of DNA on a chromosome whose specific nucleotide sequence encodes a protein.

Central Dogma

The foundational principle describing the directional flow of genetic information within biological cells: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$.

Messenger RNA (mRNA)

A type of RNA that carries the protein-encoding information copied directly from a gene in DNA to the ribosome for translation.

Transfer RNA (tRNA)

A connector RNA molecule that carries a specific amino acid to its designated site along an mRNA molecule by matching its anticodon to the mRNA codon.

Ribosomal RNA (rRNA)

A form of RNA that combines with proteins to construct a ribosome, the physical cellular site where translation occurs.

Transcription

The biochemical process in which a cell uses the nucleotide sequence of a DNA gene template to synthesize a complementary strand of RNA.

Promoter

A specific DNA sequence that signals the start of a gene and serves as the binding and unwinding site for RNA polymerase.

RNA Polymerase

The enzyme that unwinds the DNA double helix at a promoter and joins complementary RNA nucleotides along the template strand during transcription.

Terminator

A specific nucleotide sequence in DNA that marks the end of a gene, triggering RNA polymerase, DNA, and the synthesized RNA to detach from one another.

Introns

Non-coding sequences within eukaryotic genes that are transcribed into pre-mRNA but removed during RNA processing before translation.

Exons

The coding nucleotide sequences of a eukaryotic gene that specify amino acids and are spliced together to form mature mRNA.

Codon

A triplet sequence of three consecutive mRNA nucleotides that encodes a single specific amino acid or signals translation termination.

Anticodon

A three-base sequence located on a tRNA molecule that complementary base-pairs with a corresponding triplet codon on an mRNA transcript.

Release Factor

A specialized protein that binds directly to a stop codon at the termination stage of translation, halting polypeptide elongation because no matching tRNA exists.

Operon

A cluster of related genes found in prokaryotes under the control of a single promoter and operator that are transcribed together.

lac Operon

An operon in bacteria consisting of three genes that encode enzymes necessary to break down lactose.

Repressor Protein

A regulatory protein that binds to an operator sequence on bacterial DNA, physically blocking RNA polymerase from transcribing operon genes.

Transcription Factors

A group of distinct regulatory proteins in eukaryotes that bind to DNA sequences to modulate RNA polymerase activity and regulate transcription rates.

Alternative Splicing

A eukaryotic gene regulation mechanism where different combinations of exons from a single pre-mRNA transcript are joined, generating multiple distinct proteins from one gene.

Apoptosis

Programmed cell death that coordinates the elimination of unnecessary cells to carve out distinctive structures during embryonic development.

Semiconservative Replication

The mechanism of DNA duplication where each resulting double helix preserves one original parental strand and incorporates one newly synthesized daughter strand.

Helicase

An enzyme that unwinds and unzips the DNA double helix ahead of the replication fork by breaking hydrogen bonds between base pairs.

DNA Polymerase

An enzyme that synthesizes new complementary DNA strands using existing template strands and proofreads the newly incorporated nucleotides.

Ligase

An enzyme that seals breaks in the sugar-phosphate backbone by joining short, newly synthesized DNA fragments into continuous strands.

Origins of Replication

Specific points along eukaryotic chromosomes where DNA replication begins simultaneously in both directions.

Binary Fission

An asexual mode of reproduction in bacteria and archaea that duplicates the single circular chromosome and distributes one copy to each daughter cell.

Chromatin

The uncoiled, loosely packed complex of DNA and associated proteins visible in the eukaryotic nucleus prior to chromosome condensation.

Sister Chromatids

Two identical copies of a replicated eukaryotic chromosome joined together at a shared centromere.

Centromere

A constricted chromosomal region where replicated sister chromatids attach to each other and where spindle fibers bind during cell division.

Cell Cycle

The continuous, regulated sequence of events extending from the beginning of one eukaryotic cell division to the start of the next, consisting of interphase and M phase.

Interphase

The non-dividing portion of the cell cycle during which cells carry out everyday biological tasks, grow, and replicate their DNA, encompassing $G_1$, $S$, and $G_2$ phases.

$$G_1\text{ Phase}$$

The primary growth stage of interphase where normal cellular functions, active transport, and general protein synthesis proceed.

$$S\text{ Phase}$$

The synthetic phase of interphase during which the entire eukaryotic genome is replicated, permanently committing the cell to division.

$$G_2\text{ Phase}$$

The final stage of interphase during which specialized proteins essential for nuclear division are produced and the cell confirms complete DNA replication.

Mitosis

The division of the eukaryotic cell nucleus into two daughter nuclei, each retaining an identical complement of parental DNA.

Spindle

A dynamic cytoskeletal structure assembled from microtubules that coordinates chromosome attachment, alignment, and separation during division.

Prophase

The first phase of mitosis characterized by chromosome condensation, spindle apparatus assembly, and disintegration of the nuclear envelope.

Metaphase

The second phase of mitosis during which spindle fibers arrange the condensed chromosomes along the equatorial plane of the cell.

Anaphase

The mitotic phase wherein centromeres split and sister chromatids are pulled apart toward opposite poles by shortening spindle fibers.

Telophase

The final mitotic phase where separated chromosomes decondense at opposing cell poles, new nuclear envelopes and nucleoli form, and the spindle dissolves.

Cytokinesis

The physical division of the cytoplasm and organelles that separates a dividing cell into two distinct daughter cells.

Cleavage Furrow

An indentation along the middle of a dividing animal cell generated by a contractile ring of microfilaments that pinches the cell in two.

Cell Plate

A precursor structure formed by vesicles gathering at the center of a dividing plant cell to deliver cellulose and polysaccharides for building new cell walls.

Tumor

An abnormal, uncontrolled mass of tissue that develops when cells bypass cell division checkpoints.

Benign Tumor

An abnormal cellular mass that remains enclosed, non-invasive, and confined to its original tissue site.

Malignant Tumor

A cancerous mass of cells that invades surrounding healthy tissues and possesses the potential to spread throughout the body.

Meiosis

A specialized reductional cell division process in germ cells involving one DNA replication and two nuclear divisions, producing four nonidentical haploid gametes.

Homologous Chromosomes

A matched pair of maternal and paternal chromosomes in a diploid cell that share the same length, centromere position, and gene loci.

Crossing Over

The physical exchange of homologous chromosome fragments during prophase I of meiosis that yields new combinations of alleles on recombinant chromatids.

Independent Assortment

The random orientation of homologous chromosome pairs along the metaphase I plate in meiosis, creating numerous distinct chromosome combinations in resulting gametes.

Monozygotic Twins

Genetically identical offspring that develop when a single early embryo derived from one fertilized zygote cleaves into two independent individuals.

Dizygotic Twins

Fraternal offspring with unique DNA profiles resulting from two distinct sperm cells fertilizing two separate egg cells within the same pregnancy.

Nondisjunction

The failure of homologous chromosomes to segregate during anaphase I or sister chromatids to separate during anaphase II, leading to gametes with abnormal chromosome numbers.

Triplo-X

A condition caused by nondisjunction resulting in females possessing three X chromosomes ($XXX$), with an approximate incidence of $1\text{ in }1500$ females.

Klinefelter Syndrome

A sex chromosome disorder in males caused by an $XXY$ chromosomal constitution, occurring in approximately $1\text{ in }750$ males.

Jacobs Syndrome

A sex chromosome abnormality characterized by an $XYY$ genotype, occurring in approximately $1\text{ in }1000$ males.

Turner Syndrome

A female chromosomal disorder resulting from the presence of only a single X chromosome ($XO$), occurring in approximately $1\text{ in }2000$ females.

Allele

One of two or more alternative functional variants of a specific gene residing at the same locus on homologous chromosomes.

Dominant Allele

An allele whose associated phenotypic effect is exerted and manifested whenever it is present in either a homozygous or heterozygous state.

Recessive Allele

An allele whose phenotypic expression is entirely masked whenever a corresponding dominant allele is present in the genotype.

Genotype

The underlying combination of two alleles possessed by an individual organism for a given gene.

Phenotype

The observable physical attributes or biochemical traits expressed by an organism, determined by genotype-environment interactions.

Homozygous Dominant

The genotype of an organism containing two identical dominant alleles for a specific gene.

Heterozygous

The genotype of an individual possessing two different alleles (one dominant and one recessive) for a particular gene.

Homozygous Recessive

The genotype of an organism that possesses two identical recessive alleles for a specified gene.

Test Cross

A mating between an individual showing a dominant phenotype but an unknown genotype and a homozygous recessive individual to deduce the unknown genotype.

Law of Segregation

Mendel's principle establishing that the two alleles for each gene separate during meiosis so that each gamete carries only one allele for that gene.

Law of Independent Assortment

Mendel's principle stating that alleles of distinct genes located on different chromosomes package into gametes independently of one another.

Monohybrid Cross

A genetic mating between two individuals that are both heterozygous for a single gene.

Dihybrid Cross

A cross between individuals that are heterozygous for two unlinked genes, typically generating a classic $9:3:3:1$ phenotypic ratio.

Product Rule

A mathematical probability rule that calculates the likelihood of independent inheritance events occurring simultaneously by multiplying their individual probabilities.

Linked Genes

Genes situated near each other on the same chromosome that do not assort independently and are usually inherited together as a unit.

Linkage Map

A diagram mapping the linear arrangement and relative physical distances between genes on a chromosome based on crossover recombination frequencies.

Incomplete Dominance

An inheritance pattern in which neither allele masks the other, resulting in a heterozygous phenotype intermediate between both homozygous phenotypes.

Codominance

An inheritance pattern where both alleles are simultaneously and fully expressed in the heterozygote without masking one another, as seen in ABO blood type $AB$.

Pleiotropy

A genetic phenomenon wherein a single gene exerts multiple distinct and seemingly unrelated phenotypic effects across various tissues or pathways, as in Marfan syndrome.

X-Linked Trait

A trait governed by alleles located on the X chromosome that exhibits distinctive inheritance patterns and affects males disproportionately.

X-Inactivation

The random transcriptional silencing of one of the two X chromosomes in each somatic cell of an $XX$ female to prevent a double dose of gene products.

Polygenic Trait

A phenotypic characteristic, such as human skin color, whose variation is controlled by the additive effects of multiple distinct genes.

Pedigree

A standardized genealogical chart depicting familial relationships and phenotypic records across successive generations to determine modes of inheritance.