BIO 101 Exam 3 Study Guide: The Cell Cycle, Meiosis, Mendelian Genetics, Chromosomal Inheritance, Molecular Genetics, and Gene Expression

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Chapter 12: The Cell Cycle

Overview of the Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide. It ensures the accurate duplication and distribution of genetic material to daughter cells.

Interphase: The period of cell growth and DNA replication, consisting of G1 (growth), S (DNA synthesis), and G2 (preparation for mitosis).
Mitosis: Division of the nucleus, followed by cytokinesis (division of the cytoplasm).
Key Roles of Cell Division: Growth, repair, and asexual reproduction in multicellular organisms.
Genetically Identical Daughter Cells: Produced by mitosis, each with the same number and type of chromosomes as the parent cell.

Key Terms

Genome: The complete set of an organism's genetic material.
Chromosomes: Structures that organize and carry genetic information.
Chromatin: DNA and protein complex that makes up chromosomes.
Somatic Cells vs. Gametes: Somatic cells are body cells (diploid), while gametes are reproductive cells (haploid).
Sister Chromatids: Identical copies of a chromosome connected at the centromere.
Centromere: Region where sister chromatids are joined.

Phases of Mitosis

Prophase: Chromatin condenses into chromosomes; mitotic spindle begins to form.
Prometaphase: Nuclear envelope fragments; spindle fibers attach to kinetochores.
Metaphase: Chromosomes align at the metaphase plate.
Anaphase: Sister chromatids separate and move toward opposite poles.
Telophase: Nuclear envelopes reform; chromosomes decondense.

Cytokinesis

Animal Cells: Cleavage furrow forms to divide the cytoplasm.
Plant Cells: Cell plate forms, leading to new cell wall formation.

Other Key Concepts

Binary Fission: Prokaryotic cell division, simpler than mitosis.
Cancer Cells: Cells that escape normal cell cycle controls, leading to uncontrolled division.
Cell Cycle Control System: Regulates progression through the cell cycle using checkpoints (G1, G2, M).
G0 Phase: Non-dividing state.
Benign vs. Malignant Tumors: Benign tumors do not spread; malignant tumors invade tissues (metastasis).

Chapter 13: Meiosis

Introduction to Meiosis

Meiosis is the process by which gametes (sperm and eggs) are produced, reducing the chromosome number by half and increasing genetic diversity.

Genes: Units of heredity located on chromosomes.
Gametes vs. Somatic Cells: Gametes are haploid; somatic cells are diploid.
Locus: Specific location of a gene on a chromosome.
Asexual vs. Sexual Reproduction: Asexual produces identical offspring; sexual combines genes from two parents.
Karyotype: Ordered display of chromosome pairs.
Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.
Autosomes vs. Sex Chromosomes: Autosomes are non-sex chromosomes; sex chromosomes determine sex.
Diploid (2n) vs. Haploid (n): Diploid cells have two sets of chromosomes; haploid have one.

Phases of Meiosis

Meiosis I: Homologous chromosomes separate, producing two haploid cells.
Meiosis II: Sister chromatids separate, resulting in four genetically unique haploid cells.
Prophase I: Crossing over occurs at chiasmata, increasing genetic variation.
Metaphase I: Homologous pairs align randomly at the metaphase plate (independent assortment).
Anaphase I: Homologous chromosomes separate.

Comparison: Mitosis vs. Meiosis

Mitosis: Produces two identical diploid cells; one division.
Meiosis: Produces four unique haploid cells; two divisions.

Genetic Variation Mechanisms

Independent assortment of chromosomes
Crossing over
Random fertilization

Chapter 14: Mendel and the Gene Idea

Foundations of Genetics

Gregor Mendel's experiments with pea plants established the basic principles of heredity.

Characters and Traits: Characters are heritable features; traits are variants of characters.
True-Breeding: Organisms that produce offspring identical to themselves.
P, F1, F2 Generations: Parental, first filial, and second filial generations in Mendel's crosses.
Dominant vs. Recessive Traits: Dominant traits mask recessive ones in heterozygotes.
Mendel’s 4 Concepts: 1) Alternative versions of genes (alleles), 2) Organisms inherit two alleles, 3) Dominant allele determines appearance, 4) Law of segregation.
Homozygous vs. Heterozygous: Homozygous has two identical alleles; heterozygous has two different alleles.
Phenotype vs. Genotype: Phenotype is physical appearance; genotype is genetic makeup.
Testcross: Cross with a homozygous recessive to determine genotype.
Dihybrid Cross: Cross involving two traits.

Extensions of Mendelian Genetics

Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., pink flowers).
Codominance: Both alleles expressed (e.g., AB blood type).
Multiple Alleles: More than two alleles exist for a gene (e.g., ABO blood group).
Pleiotropy: One gene affects multiple traits (e.g., sickle cell disease).
Epistasis: One gene affects expression of another (e.g., coat color in mice).
Polygenic Inheritance: Multiple genes affect a trait (e.g., skin color).
Environmental Impact: Phenotype can be influenced by environment.

Human Genetics

Inherited Disorders: Caused by recessive or dominant alleles.
Carriers: Heterozygotes for a recessive disorder.
Examples: Sickle cell disease, multifactorial disorders.

Chapter 15: Chromosomal Basis of Inheritance

Chromosomes and Inheritance

Morgan’s Experiments: Used fruit flies to show genes are on chromosomes.
Wild Type vs. Mutants: Wild type is the normal phenotype; mutants have altered traits.
Sex Determination: XY system in humans; sex-linked genes are on sex chromosomes.
X-Linked Disorders: More common in males (e.g., color blindness, hemophilia).
Barr Body: Inactivated X chromosome in females; leads to mosaicism.
Linked Genes: Genes located close together on the same chromosome.

Chromosomal Alterations

Nondisjunction: Failure of chromosomes to separate properly.
Aneuploidy: Abnormal number of chromosomes (monosomic, trisomic).
Polyploidy: More than two sets of chromosomes (common in plants).
Structural Changes: Deletion, duplication, inversion, translocation.

Human Disorders

Down Syndrome: Trisomy 21.
Klinefelter Syndrome: XXY males.
Triple X Syndrome: XXX females.
Turner Syndrome: Monosomy X (XO females).
Cri du Chat: Deletion on chromosome 5.

Other Inheritance Patterns

Genomic Imprinting: Expression of an allele depends on parent of origin.
Extranuclear Genes: Genes in mitochondria and chloroplasts are inherited maternally.

Chapter 16: Molecular Basis of Inheritance

Discovery of DNA as Genetic Material

Morgan: Genes are located on chromosomes.
Griffith: Discovered transformation in bacteria.
Oswald, McCarty, MacLeod: Identified DNA as the transforming molecule.
Hershey and Chase: Showed DNA, not protein, is genetic material using bacteriophages.
Chargaff’s Rules: Amount of A = T, G = C in DNA.
Rosalind Franklin: X-ray diffraction images revealed DNA’s helical structure.
Watson and Crick: Built the double helix model of DNA.

DNA Structure and Replication

Double Helix: Two antiparallel strands.
Semiconservative Model: Each new DNA has one old and one new strand.
Origins of Replication: Sites where DNA replication begins.
Replication Fork: Y-shaped region where DNA is unwound.

Enzymes and Proteins in DNA Replication

Helicase: Unwinds DNA.
Single-Strand Binding Proteins: Stabilize unwound DNA.
Topoisomerase: Relieves strain ahead of replication fork.
Primase: Synthesizes RNA primer.
DNA Polymerases: Add nucleotides to new DNA strand.
Leading vs. Lagging Strand: Leading is continuous; lagging is discontinuous (Okazaki fragments).
DNA Ligase: Joins Okazaki fragments.
Mismatch Repair: Corrects errors after replication.
Nucleotide Excision Repair: Removes and replaces damaged DNA.
Telomeres: Repetitive DNA at chromosome ends; protect from degradation.
Chromatin, Histones, Nucleosome: DNA packaging in eukaryotes.

Chapter 17: Gene Expression

Central Dogma of Molecular Biology

Central Dogma: Information flows from DNA to RNA to protein.
Gene Expression: Process by which DNA directs protein synthesis.

Transcription and Translation

Transcription: Synthesis of RNA from DNA template; occurs in nucleus (eukaryotes) or cytoplasm (prokaryotes).
Translation: Synthesis of protein from mRNA; occurs in cytoplasm.
Genetic Code: Triplet code; 64 codons (61 for amino acids, 3 stop codons); universal and redundant.
Start Codon: AUG (methionine).
RNA Polymerase: Enzyme that synthesizes RNA.
mRNA Modification (Eukaryotes): 5’ cap, poly-A tail, RNA splicing (removal of introns, joining of exons), alternative splicing.

Translation Details

tRNA: Transfers amino acids to ribosome; has anticodon complementary to mRNA codon.
Ribosome Sites: A (aminoacyl), P (peptidyl), E (exit).
Stages of Translation: Initiation, elongation, termination.
Post-Translational Modifications: Folding and chemical modifications of proteins.
Polyribosomes: Multiple ribosomes translating a single mRNA.

Mutations and Gene Editing

Point Mutations: Single nucleotide changes (substitutions, insertions, deletions).
Silent, Missense, Nonsense Mutations: Silent (no effect), missense (change amino acid), nonsense (introduce stop codon).
Mutagens: Agents that cause mutations.
CRISPR: Tool for gene editing.
Gene: Region of DNA that codes for a functional product.

Comparison Table: Mitosis vs. Meiosis

Feature	Mitosis	Meiosis
Number of Divisions	1	2
Number of Daughter Cells	2	4
Genetic Composition	Identical	Unique
Chromosome Number	Diploid (2n)	Haploid (n)
Role	Growth, repair	Gamete production

Key Equations and Concepts

Law of Segregation: Each allele segregates into separate gametes.
Law of Independent Assortment: Alleles of different genes assort independently.
Chargaff’s Rules: ,
Semiconservative Replication:

Additional info: These notes expand on the study guide by providing definitions, explanations, and examples for each key concept, as well as a comparison table and relevant equations for exam preparation.