Comprehensive Biology: Genetics, Molecular Biology, Gene Regulation, and Biotechnology

Practice vocabulary flashcards covering classical Mendelian genetics, meiosis, chromosomal inheritance, DNA structure and replication, gene expression, eukaryotic and prokaryotic gene regulation, and core biotechnology applications.

Law of Segregation

A Mendelian principle stating that during gamete formation, the two alleles for a trait separate from one another so that each gamete carries only one allele for each gene.

Law of Independent Assortment

A Mendelian principle stating that alleles for different traits are inherited independently of one another during gamete formation, which occurs due to the random alignment of homologous chromosome pairs during Metaphase I of meiosis.

Principle of Dominance

The principle stating that when two different alleles for a trait are present in an individual, the dominant allele masks the phenotypic expression of the recessive allele.

Gene

A segment of DNA that contains the instructions for producing a specific protein or influencing a particular trait.

Allele

A specific alternative version of a gene that can produce variations in the phenotypic expression of a trait.

Genotype

The specific combination of alleles an organism possesses for a given gene or set of genes (e.g., $AA$, $Aa$, or $aa$).

Phenotype

The observable physical, physiological, or biochemical characteristics of an organism resulting from its genotype and environmental influences.

Monohybrid Cross

A genetic mating between two individuals that differ in a single trait, typically yielding a $3:1$ phenotypic ratio and a $1:2:1$ genotypic ratio in the $F_2$ generation when crossing two heterozygotes.

Test Cross

A breeding procedure in which an individual displaying a dominant phenotype of unknown genotype is crossed with a homozygous recessive individual to determine whether the dominant individual is homozygous or heterozygous.

Incomplete Dominance

An inheritance pattern in which neither allele is completely dominant over the other, causing heterozygous individuals to display an intermediate phenotype between the two homozygous phenotypes (typically showing a $1:2:1$ phenotypic ratio).

Codominance

An inheritance pattern in which both alleles in a heterozygote are fully and simultaneously expressed without blending, such as the $I^A$ and $I^B$ alleles producing the AB blood type in humans.

Sex-linkage

The pattern of inheritance for traits controlled by genes located on sex chromosomes, most commonly on the X chromosome, causing recessive traits to appear more frequently in hemizygous males.

Epistasis

A form of gene interaction where the phenotypic expression of one gene is masked or altered by another independent gene, such as the recessive epistasis in mouse coat color resulting in a $9:3:4$ phenotypic ratio.

Chromosomal Theory of Inheritance

The unifying biological theory developed by Walter Sutton and Theodor Boveri stating that genes are located at specific linear loci on chromosomes and that chromosome behavior during meiosis explains Mendelian inheritance patterns.

Genetic Linkage

The tendency of genes located close to each other on the same chromosome to be inherited together during meiosis rather than assorting independently.

Homologous Recombination

A biological process occurring during crossing over in Prophase I of meiosis in which non-sister chromatids of homologous chromosomes exchange genetic material, generating recombinant chromosomes with novel allele combinations.

Tetrad

The four-chromatid structure formed during Prophase I of meiosis when two homologous chromosomes—each composed of two sister chromatids—pair tightly via synapsis.

Recombination Frequency

A quantitative value calculated as (\text{Number of recombinant offspring} \backslashdiv \text{Total number of offspring}) \times 100, representing the frequency of crossing over between linked genes where $1\text{ centiMorgan (cM)} = 1\text{\%}$, up to a maximum limit of $50\text{\%}$.

Karyotype

An organized photographic display of an individual's complete set of metaphase chromosomes arranged in homologous pairs according to size, shape, centromere position, and banding pattern.

Nondisjunction

An error in cell division where homologous chromosomes fail to separate during Meiosis I or sister chromatids fail to separate during Meiosis II, leading to aneuploid gametes.

Aneuploidy

A chromosomal condition in which an individual has an abnormal number of chromosomes due to the loss ($2n - 1$, monosomy) or gain ($2n + 1$, trisomy) of a single chromosome.

Trisomy 21

A human genetic condition, commonly known as Down Syndrome, caused by nondisjunction that results in three copies of chromosome 21 ($2n + 1$).

Klinefelter Syndrome

A human chromosomal abnormality affecting males characterized by the presence of an extra X chromosome, resulting in a $47,\text{XXY}$ karyotype.

Turner Syndrome

A human chromosomal abnormality affecting females characterized by the complete or partial absence of one X chromosome, resulting in a $45,\text{X}$ karyotype.

Chromosomal Inversion

A structural chromosome rearrangement occurring when a segment breaks off, rotates 180^\text{\circ}, and reinserts in reverse orientation, categorized as pericentric if it includes the centromere or paracentric if it does not.

Chromosomal Translocation

A structural abnormality occurring when a segment of one chromosome breaks off and attaches to a non-homologous chromosome, which may be balanced (reciprocal) or unbalanced.

Chromosomal Deletion

A structural chromosomal abnormality involving the permanent loss of a chromosomal segment and its corresponding genetic material.

Chromosomal Duplication

A structural chromosomal abnormality in which a segment of a chromosome is copied, resulting in redundant genetic material.

Polyploidy

A genetic condition in which an organism possesses one or more complete extra sets of chromosomes beyond the normal diploid number (e.g., $3n$, $4n$), which is common in plants.

Transformation

The process first discovered by Frederick Griffith in Streptococcus pneumoniae in which living nonpathogenic bacterial cells take up foreign genetic material from dead cells, altering their genotype and phenotype.

Chargaff's Rules

The biochemical principle established by Erwin Chargaff stating that in any double-stranded DNA sample, the amount of adenine equals thymine ($A = T$) and the amount of cytosine equals guanine ($C = G$).

Semi-Conservative Replication

The mechanism of DNA replication demonstrated by Meselson and Stahl where each replicated double-stranded DNA molecule contains one original parental strand and one newly synthesized daughter strand.

Helicase

An enzyme that unwinds the DNA double helix at the replication fork by breaking the hydrogen bonds that hold complementary base pairs together.

Single-Stranded Binding Proteins (SSBs)

Proteins that bind to exposed single strands of template DNA during replication to stabilize them and prevent them from re-annealing into a double helix.

Topoisomerase

An enzyme that cuts, uncoils, and reseals DNA strands ahead of the replication fork to relieve supercoiling and torsional strain caused by helicase unwinding.

RNA Primase

An enzyme that synthesizes short complementary RNA primers that provide the free $3'\text{-OH}$ group required by DNA polymerase to initiate strand synthesis.

DNA Polymerase

An enzyme that synthesizes new DNA strands by adding complementary deoxyribonucleotides one by one to the $3'$ end of a pre-existing strand or primer in the $5' \rightarrow 3'$ direction, while also performing proofreading exonuclease activity.

DNA Ligase

An enzyme that facilitates the joining of DNA strands by forming phosphodiester bonds, specifically sealing nicks between adjacent Okazaki fragments on the lagging strand.

Telomeres

Repetitive, noncoding DNA-protein cap structures at the ends of linear eukaryotic chromosomes that serve as protective buffers against the end-replication problem and prevent chromosome fusion.

Telomerase

An enzyme containing an internal RNA template that elongates telomeres at the ends of eukaryotic chromosomes, maintaining chromosome integrity in germ cells and stem cells.

Nucleotide Excision Repair (NER)

A DNA repair mechanism that detects and removes bulky, helix-distorting lesions such as UV-induced thymine dimers by excising an oligonucleotide fragment of approximately $12\text{--}24$ nucleotides.

Sanger Sequencing

A chain-termination method of DNA sequencing that utilizes modified dideoxynucleosides ($\text{ddNTPs}$) lacking a $3'\text{-OH}$ group, terminating DNA synthesis at specific bases to produce labeled fragments separated by size via capillary electrophoresis.

Central Dogma

The fundamental framework of molecular biology describing the unidirectional flow of genetic information: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$.

TATA Box

A highly conserved promoter DNA sequence (typically $\text{TATAAA}$) located roughly $25\text{--}35$ base pairs upstream of the transcription start site in eukaryotic genes that binds transcription factors to position RNA polymerase II.

Transcription Factors

Regulatory proteins in eukaryotic cells that bind to specific promoter or enhancer elements to assemble a pre-initiation complex and recruit RNA polymerase II for transcription.

Alternative Splicing

A post-transcriptional process in eukaryotes where exons of a pre-mRNA are spliced in multiple arrangements, allowing a single gene to encode multiple distinct protein variants.

Silent Mutation

A point mutation in a protein-coding sequence that alters a nucleotide base without altering the amino acid sequence of the resulting polypeptide due to the redundancy of the genetic code.

Missense Mutation

A point mutation in DNA that changes a single codon so that it specifies a different amino acid, which may alter the structure and function of the encoded protein.

Nonsense Mutation

A point mutation that converts an amino acid-specifying codon into a premature stop codon ($\text{UAA}$, $\text{UAG}$, or $\text{UGA}$), leading to early termination of translation and a truncated protein.

Frameshift Mutation

A genetic mutation caused by the insertion or deletion of a number of nucleotides that is not a multiple of three, altering the translational reading frame of all downstream codons.

Operon

A functional unit of genomic DNA found in bacteria consisting of a cluster of structural genes under the control of a single promoter and operator, transcribed together as a single mRNA.

Operator

A regulatory DNA sequence located within or adjacent to a bacterial operon's promoter that binds a repressor protein to regulate transcription.

Repressor

A regulatory protein that binds to an operator sequence to physically block RNA polymerase from transcribing structural genes.

Inducible Operon

A bacterial operon (such as the lac operon) that is normally inactive and is turned on when an inducer molecule (such as allolactose) binds to the repressor, causing it to release from the operator.

Repressible Operon

A bacterial operon (such as the trp operon) that is normally active and is turned off when an end-product corepressor (such as tryptophan) binds to the repressor, enabling it to bind to the operator.

Histone Acetylation

An epigenetic modification in which acetyl groups are added to histone tails, reducing their positive charge, relaxing chromatin packaging, and making DNA accessible for transcription.

DNA Methylation

An epigenetic mechanism involving the addition of methyl groups to DNA molecules (and histones), which condenses chromatin structure and typically represses gene transcription.

Enhancer

A distal regulatory DNA sequence in eukaryotes that binds activator proteins, which loop DNA with the help of DNA bending proteins to interact with promoter complexes and increase transcription.

MicroRNAs (miRNAs)

Small noncoding regulatory RNA molecules approximately $20\text{--}22$ nucleotides long that, after processing by the enzyme Dicer, associate with the RISC complex to bind target mRNAs and cause translational repression or mRNA degradation.

Proto-oncogene

A normal cellular gene that encodes proteins promoting cell growth and division, which can transform into an oncogene driving cancer progression when mutated or abnormally overexpressed.

Tumor Suppressor Gene

A gene that normally produces proteins that slow the cell cycle, repair DNA, or trigger apoptosis, whose loss of function or epigenetic silencing promotes uncontrolled cell proliferation.

Restriction Enzyme

A specialized endonuclease originally discovered in bacteria that recognizes specific short nucleotide sequences (recognition sites) and cleaves double-stranded DNA into precise fragments.

Sticky Ends

Short, single-stranded overhangs produced when a restriction enzyme cuts the two strands of a DNA molecule at offset positions, allowing compatible complementary fragments to base-pair.

Blunt Ends

Non-overhanging double-stranded DNA termini created when a restriction enzyme cleaves both complementary strands straight across at the exact same nucleotide position.

Gel Electrophoresis

A laboratory technique that separates DNA fragments by size by applying an electric current across an agarose gel, drawing negatively charged DNA toward the positive electrode where smaller fragments migrate farther than larger ones.

Restriction Fragment Length Polymorphism (RFLP)

A molecular analysis method that evaluates genetic differences among individuals by digesting DNA with restriction enzymes and analyzing the resulting variable fragment lengths via gel electrophoresis.

Molecular Cloning

A laboratory procedure used to generate multiple identical copies of a specific gene or DNA sequence by inserting it into a plasmid vector and propagating it within bacterial cells.

Reproductive Cloning

A biotechnology procedure, typically using somatic cell nuclear transfer (SCNT), designed to generate an entire multicellular organism that is genetically identical to the nucleus donor.

Plasmid

A small, circular, extrachromosomal DNA molecule found in bacteria that replicates independently of chromosomal DNA and is frequently used as a vector in genetic engineering.

CRISPR-Cas9

A targeted genome-editing system that enables researchers to alter, insert, or knock out specific DNA sequences in an organism to study gene function and develop clinical therapies.