Comprehensive Genetics and Cell Biology Review

Sixty-five vocabulary flashcards covering gene regulation, epigenetics, cell division, meiosis, Mendelian genetics, mathematical inheritance, and non-Mendelian complex traits.

Prokaryotic Gene Regulation

Gene regulation that occurs primarily at the transcriptional level in single-celled organisms to rapidly adapt to environmental changes like food availability.

Eukaryotic Gene Regulation

A multi-step regulatory process occurring at transcription, RNA processing, translation, and post-translation to drive cell differentiation despite cells having the same genome.

General Transcription Factors

Proteins that bind the core promoter (TATA box) to recruit RNA Polymerase II, creating a low, basal transcription rate.

Regulatory Transcription Factors

Activators or repressors that bind cis-regulatory elements (enhancers or silencers) to heavily increase or decrease the transcription rate.

The Mediator

A multiprotein complex that physically bridges regulatory transcription factors to the general transcription factor and RNA Polymerase II complex.

Transcription Factor Motifs

Specific 3D structural shapes within transcription factor domains—such as helix-turn-helix, zinc finger, or leucine zipper—that recognize specific nucleotide sequences.

Major Groove of DNA

The outer groove of the DNA double helix where transcription factors bind and recognize specific base sequences without unwinding the double helix.

Modulation of Regulatory Transcription Factors

The three mechanisms regulating transcription factors: binding of small effector molecules, protein-protein interactions (such as dimerization), and covalent modifications (such as phosphorylation).

Glucocorticoid Receptor

A regulatory transcription factor located in the cytosol that binds steroid hormones, releases Hsp90, dimerizes, and translocates into the nucleus.

Hsp90

A chaperone protein bound to the glucocorticoid receptor in the cytosol that is released upon hormone binding.

Glucocorticoid Response Element (GRE)

An enhancer DNA sequence in the nucleus bound by dimerized glucocorticoid receptors to activate stress-response genes.

ATP-Dependent Chromatin Remodeling

A mechanism whereby multiprotein complexes hydrolyze ATP to shift nucleosome positions, evict histones, or swap histone variants to expose the promoter.

Histone Acetyltransferases (HATs)

Enzymes that add acetyl groups to histone tails, neutralizing positive charges to repel DNA and establish open, transcriptionally active euchromatin.

Histone Deacetylases (HDACs)

Enzymes that remove acetyl groups from histone tails, restoring positive charges that tightly wrap DNA into condensed, silenced heterochromatin.

Euchromatin

Open, decondensed chromatin created by histone acetylation that is transcriptionally active.

Heterochromatin

Condensed, tightly packed chromatin created by histone deacetylation that is transcriptionally silenced.

DNA Methyltransferases

Enzymes that attach methyl groups specifically to cytosines in CpG islands or enhancers to silence gene expression.

CpG Islands

Cytosine- and guanine-rich regions near promoters where DNA methylation blocks transcription factor binding and recruits chromatin-condensing proteins.

Methyl-CpG-Binding Proteins

Proteins that recognize methylated CpG islands and recruit histone deacetylases (HDACs) to tightly condense chromatin.

Insulators

DNA sequences that bind specific proteins to act as physical barriers, preventing an enhancer meant for one gene from activating a neighboring gene.

Alternative Splicing

A post-transcriptional process of removing introns and joining exons that enables a single pre-mRNA to produce multiple distinct proteins.

Poly-A Tail

A terminal modification on mRNA whose length dictates the transcript lifespan and stability in the cytosol prior to degradation.

RNA Interference (RNAi)

A cytosolic post-transcriptional regulatory mechanism where miRNAs or siRNAs bind mature mRNA to physically block ribosome translation or recruit enzymes for mRNA degradation.

Nucleoid Region

The unbound, non-membrane-enclosed area in a prokaryotic cell containing a single circular chromosome devoid of histones.

Mitosis

A eukaryotic cell division process that produces two genetically identical diploid ($2n$) somatic body cells.

Meiosis

A reductional cell division process that produces four genetically distinct haploid ($n$) gametes.

Spermatogenesis

Male gametogenesis involving equal cytokinesis to produce four equal, functional sperm cells.

Oogenesis

Female gametogenesis involving unequal cytokinesis to produce one large functional ovum and two to three non-functional polar bodies that degrade.

Polar Bodies

Small, non-functional cells produced by unequal cytokinesis during oogenesis that degrade to conserve nutrients and cytoplasm for the single surviving ovum.

Crossing Over

A meiotic process in Prophase I where non-sister chromatids of homologous chromosomes exchange DNA segments.

Chiasma

The anatomical point of contact formed between non-sister chromatids of homologous chromosomes during crossing over.

Law of Independent Assortment

Mendelian principle occurring during Metaphase I based on the random alignment of maternal and paternal homologous chromosome pairs at the metaphase plate.

Law of Segregation

Mendelian principle physically occurring in Anaphase I when homologous chromosomes pull apart, ensuring each gamete receives only one allele per trait.

SRY Gene

A gene on the human Y chromosome encoding a regulatory transcription factor that initiates testis development.

Aromatase

An enzyme in temperature-dependent sex determination species that converts testosterone to estrogen in response to environmental incubation temperatures.

Allele

A specific variant or alternate form of a gene (such as blonde versus brown hair color).

Sister Chromatids

Identical copies of a replicated chromosome joined together at the centromere.

Homologous Chromosomes

A maternal and paternal pair of chromosomes containing the same genes in the same sequence, but potentially bearing different alleles.

Centrosome (MTOC)

The microtubule-organizing center located at cell poles that nucleates and anchors spindle fibers during division.

Centromere

The constricted DNA waist region of a chromosome that holds sister chromatids together.

Kinetochore

A specialized multiprotein complex located over the centromeric DNA where spindle microtubule fibers attach during division.

Tetrad

A structure formed during Prophase I of meiosis composed of two paired homologous chromosomes, totaling four chromatids.

True-Breeding

Homozygous parental organisms that consistently yield offspring with identical traits upon self-fertilization.

Unlinked Traits

Traits whose underlying genes reside on separate chromosomes (or far apart on the same chromosome), allowing them to assort independently.

Monohybrid Cross Ratios

The standard offspring ratios from a cross between single-gene heterozygotes ($Aa \times Aa$): a $3:1$ phenotypic ratio and a $1:2:1$ genotypic ratio.

Dihybrid Cross Ratios

The standard $9:3:3:1$ phenotypic ratio produced from a cross between individuals heterozygous for two unlinked traits ($AaBb \times AaBb$).

Product Rule

A probability rule used for independent events occurring in a specific sequence: $P(A \text{ and } B) = P(A) \times P(B)$.

Binomial Expansion Formula

A probability equation used for unordered combinations of events: $P = \frac{n!}{x!\,(n-x)!}\,p^x q^{n-x}$, where $0! = 1$.

Chi-Square Null Hypothesis

A statistical hypothesis stating there is no significant difference between observed and expected Mendelian counts, failed to be rejected when $p > 0.05$.

Degrees of Freedom (Chi-Square)

A statistical metric calculated as the number of distinct phenotypic categories minus one: $DF = n - 1$.

Haplosufficient

A gene property where one functional wild-type allele produces enough protein ($50\%$) for normal phenotypic function, making mutant alleles recessive.

Haploinsufficient

A gene property where $50\%$ protein yield from a single wild-type allele is insufficient for standard function, causing mutant alleles to act dominant.

Temperature-Sensitive Allele

An allele producing a protein that folds correctly only at specific permissive temperatures and misfolds at restrictive temperatures.

Lethal Alleles

Mutations that cause death in homozygous individuals, altering the surviving monohybrid cross phenotypic ratio from $3:1$ to $2:1$.

Heterozygote Advantage

An evolutionary circumstance where the heterozygous genotype has higher fitness than either homozygote by conferring resistance to a pathogen.

Incomplete Dominance

An inheritance pattern where the heterozygote displays an intermediate phenotype because $50\%$ protein expression cannot reach the full dominant threshold.

Co-dominance

An inheritance pattern in which both distinct alleles are simultaneously and fully expressed in the heterozygote, as observed in type AB blood.

Multiple Alleles

The existence of more than two allelic variants of a single gene within a population, such as the ABO blood group system.

Incomplete Penetrance

A phenomenon where an organism inherits a dominant disease-causing genotype but fails to physically manifest the associated phenotype.

Hemizygous

Having only a single copy of a chromosome or gene, as in human males ($XY$) who carry one copy of X-linked genes.

Sex-Influenced Inheritance

An autosomal inheritance pattern where an allele is dominant in one biological sex but recessive in the other.

Sex-Limited Inheritance

An autosomal inheritance pattern where phenotypic trait expression is completely restricted to one sex due to anatomical differences.

Epistasis

A gene interaction in which alleles at one gene locus mask or suppress the phenotypic expression of alleles at an independent gene locus, altering the $9:3:3:1$ ratio to $9:7$ or $9:3:4$.

Complementation

The production of $100\%$ wild-type progeny from the mating of two mutant parents, establishing that the mutations lie in distinct genes.

Pleiotropy

A genetic condition in which a single gene locus influences multiple distinct, seemingly unrelated phenotypic traits across different tissues or organs.