Genetics, Molecular Biology, and Gene Regulation Lecture Review

Comprehensive vocabulary flashcards covering meiosis, Mendelian genetics, DNA replication, gene expression, and regulatory mechanisms from Chapters 13, 14, 16, 17, and 18.

Gene

A small segment of DNA that encodes a protein and can lead to the expression of a trait.

Allele

An alternative version of a specific gene, typically represented using capital or lowercase letters.

Cell Ploidy

The number of copies of specific genes or chromosomes found within a cell.

Haploid ($n$)

A cell condition characterized by having one copy of each gene or chromosome ("half").

Diploid ($2n$)

A cell condition characterized by having two copies of each gene or chromosome, with one copy inherited from each parent.

Karyotype

An ordered display of all the chromosomes in a cell, containing 4 copies of each chromosome.

Homologous Chromosomes

Chromosome pairs that are similar in size and shape and carry the same genes, but can have different alleles; one is paternally inherited and one is maternally inherited.

Fertilization

The process of merging haploid gametes through sperm and egg fusion to create a diploid zygote.

Zygote

The very first diploid ($2n$) cell of a new developing organism where mitosis begins.

Germ Cells

Diploid precursor cells dedicated to producing haploid gametes (sperm or egg).

Meiosis I

The reductional division phase of meiosis that reduces ploidy from diploid ($2n$) to haploid ($n$) by separating homologous chromosomes.

Meiosis II

The equational division phase of meiosis that maintains equal ploidy by separating sister chromatids, yielding 4 genetically diverse haploid gametes.

Synapsis

The process during prophase I where homologous chromosome pairs align and stick together along their DNA sequences at similar alleles.

Crossing Over

The exchange of genetic material between homologous chromosome pairs during prophase I of meiosis, also known as homologous recombination.

Chiasma

The physical attachment site where crossing over takes place between homologous chromosomes.

Independent Assortment

The random, independent alignment of homologous chromosome pairs along the metaphase plate during metaphase I, calculated by the formula $2^n$.

Nondisjunction

An error during meiosis I or II in which chromosomes fail to separate properly, resulting in aneuploid daughter cells.

Aneuploid Cells

Cells containing an abnormal number of chromosomes, having either too many or too few.

Character

An inherited feature that varies among individuals, such as plant height or flower color.

Trait

A specific variant of an inherited character, such as short versus tall or white versus purple flowers.

Law of Segregation

Mendel's principle stating that the two alleles of a gene separate during gamete formation so that each gamete receives only one copy.

Law of Independent Assortment

Mendel's principle stating that the segregation of alleles for one gene does not affect the segregation of alleles for another gene.

Genotype

The specific genetic combination of alleles present in an individual, represented by letters.

Phenotype

The physically expressed observable trait that results from an individual's genotype.

Test Cross

The breeding of an individual showing a dominant phenotype but unknown genotype with a homozygous recessive individual to determine the mystery genotype.

Incomplete Dominance

An inheritance pattern in which heterozygous individuals display a blended intermediate phenotype between the two homozygous parental traits.

Codominance

An inheritance pattern in which heterozygous individuals equally and simultaneously express both alleles in distinct patches without masking each other.

Epistasis

An inheritance pattern wherein the expression of one gene's product alters or dictates the phenotypic expression of a completely different gene.

Polygenic Trait

A single phenotypic trait that is influenced and governed by the additive effects of multiple distinct genes.

Pleiotropy

A condition in which a single gene exerts effects on multiple, seemingly unrelated phenotypic traits.

Transformation

The uptake of external, naked DNA by a bacterial cell that results in a measurable genotypic and phenotypic change.

Bacteriophage

A virus that infects and hijacks bacterial cells, composed of an external protein coat surrounding a nucleic acid core.

Semiconservative Model

The mechanism of DNA replication wherein each newly synthesized double helix contains one conserved parental strand and one newly formed strand.

Topoisomerase

An enzyme (called DNA gyrase in prokaryotes) that cuts and rejoins DNA ahead of the replication fork to relieve strain caused by DNA supercoiling.

Helicase

An enzyme that breaks hydrogen bonds between bases to unwind the DNA double helix at the replication fork, creating single-stranded templates.

Single-Stranded Binding Protein (SSB)

A protein that coats and stabilizes unwound single-stranded DNA to prevent premature reannealing and degradation.

Primase

An RNA polymerase that synthesizes short RNA primers to provide the free 3'-OH end needed for DNA polymerases to initiate synthesis.

DNA Polymerase III

The primary prokaryotic replicative enzyme responsible for building new DNA strands in the 5' to 3' direction using template strands.

DNA Polymerase I

The prokaryotic enzyme responsible for removing RNA primers and replacing them with DNA nucleotides.

DNA Ligase

An enzyme that covalently seals nicks in the phosphodiester backbone by joining Okazaki fragments on the lagging strand.

Telomeres

Non-coding repetitive nucleotide sequences situated at the ends of eukaryotic linear chromosomes that shorten with successive divisions.

Telomerase

A specialized enzyme found in germ and cancer cells that lengthens telomeric DNA repeats to maintain chromosome stability.

Promoter

A specific DNA sequence upstream of a gene that serves as the binding and attachment site for RNA polymerase to begin transcription.

Spliceosome

A large multi-component complex of RNA and proteins that excises introns from pre-mRNA and splices together exons.

Introns

Non-coding intervening sequences within eukaryotic pre-mRNA transcripts that are removed during splicing and never translated.

Exons

Coding regions within eukaryotic pre-mRNA transcripts that are spliced together and translated into protein.

Silent Mutation

A point mutation base substitution that changes a single nucleotide but results in no change to the encoded amino acid sequence.

Missense Mutation

A point mutation substitution in which a single base change alters a codon, resulting in the placement of a different amino acid into the polypeptide.

Nonsense Mutation

A point mutation that inadvertently changes an amino acid-specifying codon into a premature stop codon, terminating translation early.

Operon

A functional unit of genomic DNA in prokaryotes containing a cluster of genes with related functions controlled by a single shared promoter.

Operator

A regulatory DNA sequence within an operon where regulatory proteins, such as repressors, bind to control RNA polymerase access.

Repressor

A regulatory protein that binds to an operator to physically obstruct RNA polymerase and block transcription.

Cyclic AMP Receptor Protein (CRP)

An activator protein of the lac operon that, upon binding cyclic AMP (cAMP) when glucose is low, binds upstream of the promoter to recruit RNA polymerase.

Heterochromatin

Highly condensed, tightly packed chromosomal regions characterized by low or silenced transcriptional activity.

Euchromatin

Lightly packed, accessible chromosomal regions that exhibit high transcriptional activity and active histone acetylation.

Enhancer

A grouping of distal control elements situated far from the promoter where specific transcription factors bind to stimulate transcription.

RNA Interference (RNAi)

A post-transcriptional gene regulatory process wherein small non-coding RNAs (miRNAs or siRNAs) bind complementary mRNAs to trigger degradation or block translation.

Ubiquitin

A small regulatory peptide covalently tagged onto targeted eukaryotic proteins by ubiquitin ligase to mark them for degradation by proteases.