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

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

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 (cell 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.

Chromosomes and Genetic Material

Genome: The complete set of an organism's genetic material.
Chromosomes: Structures that organize DNA; each consists of a single DNA molecule and associated proteins.
Chromatin: DNA-protein complex that condenses to form chromosomes during cell division.
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 and spindle fibers attach during mitosis.

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, dividing 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 entered by some cells.
Benign vs. Malignant Tumors: Benign tumors do not spread; malignant tumors invade other 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 (n), somatic cells are diploid (2n).
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 an individual's chromosomes.
Homologous Chromosomes: Chromosome pairs with genes for the same traits.
Autosomes vs. Sex Chromosomes: Autosomes are non-sex chromosomes; sex chromosomes determine sex (X and Y).

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.
Similarities: Both involve chromosome duplication and separation.

Genetic Variation

Independent Assortment: Random distribution of maternal and paternal chromosomes.
Crossing Over: Exchange of genetic material between homologous chromosomes.
Random Fertilization: Any sperm can fertilize any egg, increasing variation.

Chapter 14: Mendel and the Gene Idea

Foundations of Genetics

Gregor Mendel: Father of genetics; studied inheritance in pea plants.
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 experiments.
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 of other pairs.
Alleles: Alternative versions 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 between an individual with unknown genotype and a homozygous recessive individual.
Dihybrid Cross: Cross involving two traits; reveals independent assortment.

Extensions of Mendelian Genetics

Incomplete Dominance: Heterozygote phenotype is intermediate (e.g., pink flowers from red and white parents).
Codominance: Both alleles are 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 the expression of another gene (e.g., coat color in mice).
Polygenic Inheritance: Multiple genes affect a single trait (e.g., skin color).
Environmental Impact: Environment can influence phenotype (e.g., hydrangea flower color).

Human Genetics

Inherited Disorders: Caused by recessive or dominant alleles.
Carriers: Heterozygotes for a recessive disorder allele.
Sickle Cell Disease: Example of pleiotropy and recessive disorder.
Multifactorial Disorders: Influenced by multiple genes and environment (e.g., heart disease).

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; XX = female, XY = male.
Sex-Linked Genes: Genes 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; tend to be inherited together.

Chromosomal Alterations

Nondisjunction: Failure of chromosomes to separate properly during meiosis.
Aneuploidy: Abnormal number of chromosomes (monosomic = missing one, trisomic = extra one).
Polyploidy: More than two sets of chromosomes; common in plants.
Structural Changes: Deletion, duplication, inversion, and translocation of chromosome segments.

Human Chromosomal Disorders

Disorder	Chromosomal Change	Features
Down Syndrome	Trisomy 21	Intellectual disability, characteristic facial features
Klinefelter Syndrome	XXY	Male with extra X, reduced fertility
Triple X Syndrome	XXX	Female, usually normal phenotype
Turner Syndrome	Monosomy X (XO)	Female, short stature, infertility
Cri du Chat	Deletion on chromosome 5	Intellectual disability, cat-like cry

Genomic Imprinting: Expression of an allele depends on the 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: Showed genes are on chromosomes.
Griffith: Discovered transformation in bacteria.
Oswald, McCarty, MacLeod: Identified DNA as the transforming molecule.
Hershey and Chase: Used bacteriophages to show DNA, not protein, is genetic material.
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 of nucleotides.
Semiconservative Model: Each new DNA molecule 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 strand synthesized continuously; lagging strand in Okazaki fragments.
DNA Ligase: Joins Okazaki fragments.
Mismatch Repair: Corrects errors during 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: Enzyme that synthesizes RNA.
mRNA Modification: 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-nucleotide codons specify amino acids.
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 a single mRNA.
Post-Translational Modifications: Folding and chemical modifications of proteins.

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: Gene editing technology.
Definition of a Gene: A region of DNA that can be expressed to produce a functional product.

Additional info: For equations, the following are relevant:

DNA Replication:
Law of Segregation: in gametes
Law of Independent Assortment: