Ch. 14 - Mendel and the Gene Idea

Introduction to Mendel's Experiments

Gregor Mendel's experiments with pea plants laid the foundation for modern genetics. He investigated how traits are inherited from one generation to the next.

• Key Point: Mendel used controlled crosses of pea plants to study inheritance patterns.

• Key Point: He focused on traits with two distinct forms (e.g., purple vs. white flowers).

• Example: Crossing true-breeding purple-flowered plants with white-flowered plants.

Genotype vs. Phenotype

Genotype refers to the genetic makeup of an organism, while phenotype is the observable physical or physiological trait.

• Genotype: The set of alleles an organism possesses (e.g., PP, Pp, pp).

• Phenotype: The observable trait (e.g., purple or white flowers).

• Example: Both PP and Pp genotypes result in a purple-flowered phenotype.

Punnett Squares

Punnett squares are diagrams used to predict the outcome of genetic crosses.

• Key Point: Each box represents a possible genotype of offspring.

• Example: Crossing Pp x Pp yields genotypes PP, Pp, and pp.

Mendel's Experiments

Mendel performed monohybrid and dihybrid crosses to study inheritance patterns.

• Monohybrid Cross: Involves one trait (e.g., flower color).

• Dihybrid Cross: Involves two traits (e.g., seed color and shape).

• Example: Dihybrid cross of YyRr x YyRr (yellow/round seeds).

Mendel's Laws

Mendel formulated two key laws of inheritance:

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

• Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

• Example: The inheritance of seed color does not affect the inheritance of seed shape.

Ch. 15 - The Chromosomal Basis of Inheritance

Pedigrees

Pedigrees are diagrams that show the inheritance of traits across generations in a family.

• Key Point: Used to track genetic disorders and predict inheritance patterns.

• Example: Circles represent females, squares represent males; shaded symbols indicate affected individuals.

Autosomal Inheritance

Autosomal inheritance refers to genes located on non-sex chromosomes (autosomes).

• Autosomal Dominant: Only one copy of the allele is needed for expression.

• Autosomal Recessive: Two copies of the allele are needed for expression.

• Example: Cystic fibrosis is an autosomal recessive disorder.

Sex-Linked Inheritance

Sex-linked inheritance involves genes located on sex chromosomes, usually the X chromosome.

• Key Point: Males (XY) are more likely to express X-linked recessive traits.

• Example: Hemophilia and color blindness are X-linked recessive disorders.

X-Inactivation

In female mammals, one of the two X chromosomes is randomly inactivated in each cell, forming a Barr body.

• Key Point: Ensures dosage compensation between males and females.

• Example: Calico cats have patchy fur color due to X-inactivation.

Ch. 16 - The Molecular Basis of Inheritance

The Griffith Experiment

Frederick Griffith discovered the phenomenon of transformation in bacteria, suggesting that genetic material could be transferred between cells.

• Key Point: Non-virulent bacteria became virulent when mixed with heat-killed virulent bacteria.

• Example: Mice injected with this mixture died, indicating transfer of genetic information.

The Hershey-Chase Experiment

This experiment demonstrated that DNA, not protein, is the genetic material in viruses.

• Key Point: Used radioactive labeling of DNA and protein in bacteriophages.

• Result: Only DNA entered bacterial cells and directed viral replication.

Chargaff's Rules

Erwin Chargaff found that in DNA, the amount of adenine equals thymine, and the amount of guanine equals cytosine.

• Key Point: A = T and G = C in any DNA sample.

• Implication: Base pairing is specific and complementary.

Discovering the Structure of DNA

James Watson and Francis Crick, with data from Rosalind Franklin, determined the double helix structure of DNA.

• Key Point: DNA is a double helix with antiparallel strands.

• Base Pairing: Adenine pairs with thymine; guanine pairs with cytosine.

Meselson-Stahl Experiment

This experiment confirmed that DNA replication is semiconservative.

• Key Point: Each new DNA molecule consists of one old and one new strand.

• Method: Used isotopes of nitrogen to distinguish old and new DNA strands.

Introduction to DNA Replication

DNA replication is the process by which DNA makes a copy of itself during cell division.

• Key Point: Replication is bidirectional and occurs at origins of replication.

• Enzymes: DNA polymerases, helicase, primase, ligase.

DNA Polymerases

DNA polymerases are enzymes that synthesize new DNA strands by adding nucleotides to a template strand.

• Key Point: DNA polymerase can only add nucleotides to the 3' end.

• Function: Proofreading and error correction.

Leading & Lagging DNA Strands

During replication, the two new DNA strands are synthesized differently.

• Leading Strand: Synthesized continuously in the 5' to 3' direction.

• Lagging Strand: Synthesized discontinuously as Okazaki fragments.

Steps of DNA Replication

• 1. Initiation: Helicase unwinds DNA; primase synthesizes RNA primer.

• 2. Elongation: DNA polymerase adds nucleotides.

• 3. Termination: Ligase joins Okazaki fragments; replication ends.

DNA Repair

Cells have mechanisms to repair DNA damage and maintain genetic integrity.

• Key Point: Mismatch repair, excision repair, and proofreading by DNA polymerase.

• Example: UV-induced thymine dimers are repaired by nucleotide excision repair.

Telomeres

Telomeres are repetitive DNA sequences at the ends of chromosomes that protect them from degradation.

• Key Point: Telomerase enzyme extends telomeres in germ cells and some cancer cells.

• Function: Prevents loss of genetic information during replication.

Ch. 17 - Gene Expression: From Gene to Protein

Central Dogma

The central dogma of molecular biology describes the flow of genetic information: DNA → RNA → Protein.

• Key Point: Transcription and translation are the two main processes.

• Equation:

Introduction to Transcription

Transcription is the synthesis of RNA from a DNA template.

• Key Point: Occurs in the nucleus of eukaryotic cells.

• Enzyme: RNA polymerase.

Steps of Transcription

• 1. Initiation: RNA polymerase binds to promoter region.

• 2. Elongation: RNA strand is synthesized.

• 3. Termination: RNA polymerase detaches at terminator sequence.

Eukaryotic RNA Processing and Splicing

Pre-mRNA undergoes processing before becoming mature mRNA.

• Key Point: Addition of 5' cap and 3' poly-A tail.

• Splicing: Removal of introns and joining of exons.

Introduction to Types of RNA

• mRNA (messenger RNA): Carries genetic code from DNA to ribosome.

• tRNA (transfer RNA): Brings amino acids to ribosome.

• rRNA (ribosomal RNA): Forms part of the ribosome structure.

Genetic Code

The genetic code is a set of rules by which information in mRNA is translated into proteins.

• Key Point: Codons are three-nucleotide sequences that specify amino acids.

• Example: AUG codes for methionine (start codon).

Introduction to Translation

Translation is the process by which ribosomes synthesize proteins using mRNA as a template.

• Key Point: Occurs in the cytoplasm.

• Components: mRNA, tRNA, ribosomes, amino acids.

Steps of Translation

• 1. Initiation: Ribosome assembles at start codon.

• 2. Elongation: Amino acids are added to the growing polypeptide chain.

• 3. Termination: Ribosome reaches stop codon and releases polypeptide.

Post-Translational Modification

After translation, proteins may undergo modifications that affect their function.

• Key Point: Modifications include folding, cleavage, and addition of chemical groups.

• Example: Addition of phosphate groups (phosphorylation).

Review of Transcription vs. Translation

Mutations

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

• Types: Point mutations, insertions, deletions, frameshifts.

• Effect: Can be silent, missense, or nonsense mutations.

Ch. 18 - Regulation of Gene Expression

Introduction to Regulation of Gene Expression

Gene expression is regulated to ensure that genes are expressed at the right time, place, and amount.

• Key Point: Regulation occurs at transcriptional, post-transcriptional, translational, and post-translational levels.

Prokaryotic Gene Regulation via Operons

In prokaryotes, genes are often organized into operons, which are clusters of genes under the control of a single promoter.

• Key Point: Operons allow coordinated regulation of related genes.

• Example: The lac operon in Escherichia coli.

The Lac Operon

The lac operon controls the metabolism of lactose in bacteria.

• Key Point: Inducible operon; activated in the presence of lactose.

• Regulation: Repressor protein binds operator to block transcription; lactose inactivates repressor.

Glucose's Impact on Lac Operon

Glucose availability affects lac operon expression through catabolite repression.

• Key Point: High glucose lowers cAMP, reducing lac operon activation.

• Example: Bacteria prefer glucose over lactose as an energy source.

The Trp Operon

The trp operon is a repressible operon that controls tryptophan synthesis in bacteria.

• Key Point: When tryptophan is abundant, it acts as a corepressor and shuts off the operon.

Review of the Lac Operon & Trp Operon

Introduction to Eukaryotic Gene Regulation

Eukaryotic gene expression is regulated at multiple levels, including chromatin structure and transcription initiation.

• Key Point: More complex than prokaryotic regulation due to chromatin and compartmentalization.

Eukaryotic Chromatin Modifications

Chromatin structure affects gene accessibility and expression.

• Key Point: Acetylation of histones loosens chromatin, promoting transcription.

• Methylation: Can silence genes by condensing chromatin.

Eukaryotic Transcriptional Control

Transcription factors and enhancers regulate the initiation of transcription in eukaryotes.

• Key Point: Activators bind enhancers to increase transcription; repressors decrease transcription.

Eukaryotic Post-Transcriptional Regulation

Gene expression can be regulated after transcription through mRNA processing, transport, and stability.

• Key Point: Alternative splicing produces different proteins from the same gene.

Eukaryotic Post-Translational Regulation

Protein activity can be regulated after translation by chemical modifications or degradation.

• Key Point: Ubiquitination targets proteins for degradation by the proteasome.

Ch. 20 - DNA Tools and Biotechnology

Introduction to DNA-Based Technology

DNA technology involves the manipulation and analysis of genetic material for research, medicine, and industry.

• Key Point: Includes cloning, sequencing, and genetic engineering.

Introduction to DNA Cloning

DNA cloning is the process of making multiple copies of a specific DNA segment.

• Key Point: Involves inserting DNA into a vector (e.g., plasmid) and introducing it into host cells.

Steps to DNA Cloning

• 1. Isolation: Obtain DNA of interest.

• 2. Insertion: Insert DNA into vector.

• 3. Transformation: Introduce vector into host cells.

• 4. Selection: Identify cells with recombinant DNA.

Introduction to Polymerase Chain Reaction (PCR)

PCR is a technique to amplify specific DNA sequences rapidly and precisely.

• Key Point: Uses cycles of heating and cooling with DNA polymerase.

The Steps of PCR

• 1. Denaturation: DNA strands are separated by heating.

• 2. Annealing: Primers bind to target sequences.

• 3. Extension: DNA polymerase synthesizes new DNA strands.

Gel Electrophoresis

Gel electrophoresis separates DNA fragments by size using an electric field.

• Key Point: Smaller fragments move faster through the gel.

• Application: DNA fingerprinting, analysis of PCR products.

Southern Blotting

Southern blotting detects specific DNA sequences in a sample by transferring DNA from a gel to a membrane and probing with labeled DNA.

• Key Point: Used for gene mapping and diagnosis of genetic disorders.

DNA Fingerprinting

DNA fingerprinting identifies individuals based on unique patterns in their DNA.

• Key Point: Uses variable number tandem repeats (VNTRs) or short tandem repeats (STRs).

• Application: Forensics, paternity testing.

Introduction to DNA Sequencing

DNA sequencing determines the exact order of nucleotides in a DNA molecule.

• Key Point: Essential for genomics and genetic research.

Dideoxy Sequencing

Dideoxy (Sanger) sequencing uses chain-terminating nucleotides to generate DNA fragments of varying lengths for sequence determination.

• Key Point: Fragments are separated by size to read the DNA sequence.

Ch. 21 - Genomes and Their Evolution

Genomes

A genome is the complete set of genetic material in an organism.

• Key Point: Includes all of an organism's genes and noncoding sequences.

• Genome Evolution: Involves changes in genome size, structure, and content over time.