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

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 DNA.

• Chromosomes: Structures that organize and carry genetic information.

• Chromatin: DNA-protein complex that makes up chromosomes.

• Somatic Cells vs. Gametes: Somatic cells are body cells (diploid); 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, pinching the cell in two.

• Plant Cells: Cell plate forms, dividing the cell.

Other Key Concepts

• Binary Fission: Prokaryotic cell division.

• Cancer Cells: Cells that escape normal cell cycle controls, leading to uncontrolled division.

• Cell Cycle Control System: Regulates progression through the cell cycle; includes 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

Overview of Meiosis

Meiosis is the process by which gametes (sperm and egg) 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 chromosomes.

• Homologous Chromosomes: Chromosome pairs with the same genes.

• 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: Father of genetics; studied inheritance in pea plants.

• Characters and Traits: Heritable features (characters) and variants (traits).

• 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 traits in heterozygotes.

Mendel's Laws

• Law of Segregation: Two alleles for a gene separate during gamete formation.

• Law of Independent Assortment: Each pair of alleles segregates independently (applies to genes on different chromosomes).

Genetic Vocabulary

• Alleles: Alternative forms of a gene.

• 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 (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.

• Sickle Cell Disease: Example of pleiotropy and recessive disorder.

• Multifactorial Disorders: Influenced by genes and environment.

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 = one missing, trisomic = one extra).

• 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 depends on parent of origin.

• Extranuclear Genes: Genes in mitochondria and chloroplasts; inherited maternally.

Chapter 16: Molecular Basis of Inheritance

Discovery of DNA as Genetic Material

• Morgan: Genes are on chromosomes.

• Griffith: Transformation in bacteria.

• Oswald, McCarty, MacLeod: DNA is the transforming molecule.

• Hershey and Chase: DNA, not protein, is genetic material (bacteriophage experiments).

• Chargaff's Rules: A = T, G = C in DNA.

• Rosalind Franklin: X-ray diffraction images revealed DNA's helical structure.

• Watson and Crick: Proposed 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

• Location: Nucleus in eukaryotes; cytoplasm in prokaryotes.

• Template Strand: DNA strand used to synthesize RNA.

• RNA Polymerase: Synthesizes RNA from DNA template.

• mRNA Modifications (Eukaryotes): 5’ cap, poly-A tail, RNA splicing (removal of introns, joining of exons).

• Alternative RNA Splicing: Allows one gene to code for multiple proteins.

Genetic Code

• Triplet Code: Three nucleotides (codon) specify an amino acid.

• 64 Codons: 61 code for amino acids, 3 are stop codons.

• Start Codon: AUG (methionine).

• Redundancy: Multiple codons for most amino acids; code is not ambiguous.

• Universality: Genetic code is nearly universal among organisms.

Translation

• Location: Cytoplasm (ribosomes).

• tRNA: Transfers amino acids to ribosome; has anticodon complementary to mRNA codon.

• Ribosome Sites: A (aminoacyl), P (peptidyl), E (exit).

• Stages: Initiation, elongation, termination.

• Polyribosomes: Multiple ribosomes translating one mRNA.

• Post-Translational Modifications: Folding and chemical modifications of proteins.

Mutations

• Point Mutations: Single nucleotide changes.

• Types: Silent (no effect), missense (changes amino acid), nonsense (introduces stop codon).

• Insertions/Deletions: Can cause frameshifts.

• Mutagens: Agents that cause mutations.

• CRISPR: Genome editing tool.

• Gene: Region of DNA that can be expressed to produce 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

• Semiconservative DNA Replication:

• $\text{Parent DNA} \rightarrow \text{Daughter DNA 1 (old + new)} + \text{Daughter DNA 2 (old + new)}$

• Law of Segregation (Mendel):

• $\text{Alleles separate during gamete formation so each gamete carries only one allele for each gene}$

• Law of Independent Assortment (Mendel):

• $\text{Alleles of different genes assort independently during gamete formation}$

Example: In a dihybrid cross (AaBb x AaBb), the phenotypic ratio is 9:3:3:1 if genes assort independently.

Additional info: For more details on DNA replication, see animations or videos that illustrate the process step by step.