Unit 2: DNA & Inheritance

Overview

This unit covers the molecular basis of inheritance, focusing on DNA structure and function, gene expression, cell division, mutations, cancer, and patterns of inheritance. The following study notes are organized by lesson topics and objectives, providing definitions, explanations, and examples relevant to a General Biology college course.

Lesson 9 – DNA Structure & Transcription

DNA Structure

DNA (deoxyribonucleic acid) is the hereditary material in almost all living organisms. Its structure enables the storage and transmission of genetic information.

• Nucleic acids: Polymers made of nucleotide monomers; DNA and RNA are types of nucleic acids.

• Nucleotides: The building blocks of nucleic acids, each consisting of a phosphate group, a deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, guanine).

• Chromosome: A DNA molecule with part or all of the genetic material of an organism; humans have 46 chromosomes.

• Central Dogma of Biology: Describes the flow of genetic information: DNA → RNA → Protein.

Example: The double helix structure of DNA was discovered by Watson and Crick in 1953.

Transcription

Transcription is the process by which the information in a DNA sequence is copied into messenger RNA (mRNA).

• RNA polymerase: The enzyme responsible for synthesizing RNA from a DNA template.

• Promoter: A DNA sequence where RNA polymerase binds to initiate transcription.

• mRNA: Messenger RNA, carries genetic information from DNA to the ribosome for protein synthesis.

Example: In eukaryotes, transcription occurs in the nucleus.

Chromosome Structure

• Chromatid: Each of the two thread-like strands into which a chromosome divides during cell division.

• Sister chromatid: Two identical copies of a single chromosome, connected by a centromere.

• Centromere: The region of a chromosome where the two sister chromatids are joined.

Example: During mitosis, sister chromatids are separated into two new cells.

Lesson 10 – Translation & Mutations

Translation

Translation is the process by which mRNA is decoded to produce a specific polypeptide (protein).

• Ribosome: The cellular machinery that assembles proteins from amino acids using mRNA as a template.

• Codon: A sequence of three nucleotides in mRNA that specifies an amino acid.

• Gene: A segment of DNA that codes for a protein.

Example: The codon AUG codes for the amino acid methionine and serves as the start signal for translation.

Mutations

Mutations are changes in the DNA sequence that can affect gene function and protein production.

• Types of mutations: Insertion, deletion, substitution.

• Silent mutation: A mutation that does not change the amino acid sequence of a protein.

• Missense mutation: A mutation that changes one amino acid in a protein.

• Nonsense mutation: A mutation that introduces a premature stop codon.

Example: Sickle cell anemia is caused by a missense mutation in the hemoglobin gene.

Lesson 11 – Mitosis

Cell Division: Mitosis

Mitosis is the process by which somatic (body) cells divide to produce two genetically identical daughter cells.

• Purpose: Growth, repair, and asexual reproduction.

• Phases of mitosis: Prophase, Metaphase, Anaphase, Telophase, Cytokinesis.

• Cell cycle stages: G0, G1, S, G2, M (mitosis).

• Checkpoints: Control mechanisms that ensure proper cell division (e.g., G1, G2, M checkpoints).

Example: Skin cells undergo mitosis to replace dead or damaged cells.

Somatic vs. Gamete Cells

• Somatic cells: All body cells except gametes; diploid (2n).

• Gamete cells: Sperm and egg cells; haploid (n).

Example: Muscle cells are somatic, while sperm cells are gametes.

Lesson 12 – Meiosis

Cell Division: Meiosis

Meiosis is the process by which gametes are produced, reducing the chromosome number by half and introducing genetic diversity.

• Purpose: Sexual reproduction, genetic variation.

• Phases: Meiosis I (separates homologous chromosomes), Meiosis II (separates sister chromatids).

• Key features: Crossing over, independent assortment, nondisjunction.

Example: Meiosis produces four haploid sperm cells from one diploid precursor cell.

Genetic Variation

• Crossing over: Exchange of genetic material between homologous chromosomes during Prophase I.

• Independent assortment: Random distribution of chromosomes to gametes.

• Nondisjunction: Failure of chromosomes to separate properly, leading to disorders like Down syndrome.

Example: Genetic variation is essential for evolution and adaptation.

Lesson 14 – Cancer & Patterns of Inheritance

Cancer Biology

Cancer is a group of diseases characterized by uncontrolled cell division. It can result from genetic mutations affecting cell cycle regulation.

• Benign vs. malignant tumors: Benign tumors do not invade other tissues; malignant tumors can metastasize.

• Oncogene: A gene that can cause a cell to become cancerous when mutated or overexpressed.

• Tumor suppressor gene: A gene that protects a cell from one step on the path to cancer.

Example: The p53 gene is a well-known tumor suppressor.

Patterns of Inheritance

Inheritance patterns describe how traits are passed from parents to offspring.

• Simple dominance: One allele is dominant over another.

• Codominance: Both alleles are expressed equally.

• Incomplete dominance: The phenotype is a blend of both alleles.

• Punnett Square: A diagram used to predict the outcome of a genetic cross.

Example: Blood type inheritance demonstrates codominance (A and B alleles).

Lesson 15 – Genetic Testing

Genetic Testing Methods

Genetic testing allows for the identification of genetic mutations and predispositions to diseases.

• PCR (Polymerase Chain Reaction): Technique to amplify DNA sequences.

• Gel electrophoresis: Method to separate DNA fragments by size.

• Direct-to-consumer genetic testing: Genetic tests available without a healthcare provider.

Example: PCR is used in forensic science to analyze DNA samples.

Advantages and Disadvantages

Example: Companies like 23andMe offer direct-to-consumer genetic testing.

Lesson 16 – Electrophoresis Lab

Electrophoresis

Gel electrophoresis is a laboratory technique used to separate DNA, RNA, or proteins based on size and charge.

• Application: Used in genetic testing, forensics, and research.

• Process: DNA samples are loaded into a gel, and an electric current is applied to move fragments through the gel.

Example: Electrophoresis can identify genetic mutations linked to hereditary cancers.

Lesson 17 – GR2 (Review)

This lesson serves as a review for the unit, covering all major topics: DNA structure, gene expression, cell division, mutations, cancer, inheritance patterns, and genetic testing.

Summary Table: Cell Division Comparison

Key Equations

• Central Dogma:

• Genotype Probability (Punnett Square):

Additional info: Some details, such as specific gene names and examples, were inferred to provide academic context and completeness.