Genetics, Evolution, and the Diversity of Life: Study Notes

Chapter 14: Mendel and the Gene

Genotype and Phenotype

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

• Genotype: The specific alleles present in an organism (e.g., AA, Aa, aa).

• Phenotype: The observable characteristics resulting from the genotype (e.g., flower color, seed shape).

• Example: In pea plants, the genotype RR or Rr produces round seeds (dominant phenotype), while rr produces wrinkled seeds (recessive phenotype).

Dominant and Recessive Alleles

Alleles are different forms of a gene. Dominant alleles mask the effect of recessive alleles in heterozygotes.

• Dominant allele: Expressed in the phenotype even if only one copy is present.

• Recessive allele: Expressed only when two copies are present.

• Example: In Mendel's peas, the allele for purple flowers (P) is dominant over white (p).

Inheritance of Traits

Traits are passed from parents to offspring through genes. Mendel discovered predictable patterns of inheritance.

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

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

• Punnett Square: A tool to predict offspring genotypes and phenotypes.

Mendel's Pea Plant Experiments

Mendel used controlled crosses in pea plants to uncover the basic principles of heredity.

• He observed traits such as seed shape, flower color, and pod color.

• He concluded that traits are inherited as discrete units (genes).

Chapter 15: DNA and the Gene: Synthesis and Repair

Structure of DNA

DNA is a double helix composed of nucleotides, each containing a sugar, phosphate, and nitrogenous base.

• Nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

• Base pairing: A pairs with T, C pairs with G.

• Double helix: Two strands run antiparallel and are held together by hydrogen bonds.

DNA Replication

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

• Helicase: Unwinds the DNA double helix.

• Primase: Synthesizes RNA primers to initiate replication.

• DNA Polymerase: Adds nucleotides to the growing DNA strand.

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

• Lagging strand: Synthesized discontinuously as Okazaki fragments.

• Telomeres: Repetitive sequences at chromosome ends that protect genetic information.

Base Pairing Rule

• Adenine (A) pairs with Thymine (T)

• Cytosine (C) pairs with Guanine (G)

Importance of Telomeres

• Prevent loss of important DNA during replication.

• Shorten with each cell division, contributing to aging

Chapter 16: How Genes Work

Genes and Proteins

Genes contain instructions for making proteins, which determine traits.

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

• Protein: A molecule made of amino acids that performs cellular functions.

• Central Dogma: Information flows from DNA to RNA to protein.

$\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$

From DNA to Trait

• DNA sequence determines the amino acid sequence of proteins.

• Proteins produce observable traits (e.g., pigment in flowers).

Chapter 17: Transcription, RNA Processing, and Translation

Transcription vs. Translation

Transcription and translation are the two main steps in gene expression.

• Transcription: Synthesis of RNA from a DNA template.

• Translation: Synthesis of protein from an RNA template.

Types of RNA and Their Roles

• mRNA (messenger RNA): Carries genetic information from DNA to ribosomes.

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

• Ribosomes: Molecular machines that assemble proteins.

Codons and Anticodons

• Codon: A sequence of three RNA nucleotides that codes for an amino acid.

• Anticodon: A sequence of three nucleotides in tRNA complementary to a codon.

• Start codon: Signals the beginning of translation (usually AUG).

• Stop codon: Signals the end of translation (UAA, UAG, UGA).

Location of Transcription and Translation in Eukaryotes

• Transcription occurs in the nucleus.

• Translation occurs in the cytoplasm.

Chapter 18: Control of Gene Expression in Bacteria

Gene Regulation in Bacteria

Bacteria regulate gene expression to adapt to environmental changes.

• Constitutive genes: Always active (e.g., genes for basic metabolism).

• Regulated genes: Turned on or off in response to environmental signals.

• Example: The lac operon is activated only when lactose is present.

Chapter 19: Control of Gene Expression in Eukaryotes

Gene Regulation in Eukaryotes

Different cell types express different genes, allowing for specialization.

• Chromatin: DNA wrapped around proteins called histones.

• Nucleosome: The basic unit of chromatin structure.

• Regulatory proteins: Bind to DNA to increase or decrease gene expression.

• Same DNA can produce muscle cells, nerve cells, etc., through differential gene expression.

Chapter 21: Genes, Development, and Evolution

Genes and Development

Genes control the development of organisms and changes in genes can alter body structure over time.

• Many organisms share similar developmental genes (e.g., Hox genes).

• Developmental processes provide evidence for evolution.

Chapter 22: Evolution by Natural Selection

Mechanism of Natural Selection

Natural selection is the process by which traits that increase fitness become more common in a population.

• Fitness: The ability to survive and reproduce.

• Populations evolve, not individuals.

• Evolution is not goal-directed.

• Adaptations increase survival and reproduction.

• Antibiotic resistance develops through natural selection.

Chapter 23: Evolutionary Processes

Hardy-Weinberg Equilibrium

Describes a non-evolving population where allele frequencies remain constant.

• Conditions: No mutation, random mating, no gene flow, infinite population size, no selection.

Evolutionary Mechanisms

• Mutation: Creates new genetic variation.

• Gene flow: Movement of alleles between populations.

• Genetic drift: Random changes in allele frequencies.

• Natural selection: Differential survival and reproduction.

• Heterozygote advantage: Heterozygotes have higher fitness than either homozygote.

Chapter 24: Speciation

Formation of New Species

Speciation is the process by which new species arise.

• Species: A group of organisms that can interbreed and produce fertile offspring.

• Reproductive isolation: Prevents gene flow between populations.

• Allopatric speciation: Occurs when populations are geographically separated.

• Genetic differences accumulate over time, leading to new species.

Chapter 25: Phylogenies and the History of Life

Phylogenetic Trees

Phylogenetic trees depict evolutionary relationships among species.

• Closely related species share a recent common ancestor.

• Fossils provide evidence for evolution and help calibrate phylogenies.

• Cambrian explosion: A rapid diversification of animal life about 541 million years ago.

• Mass extinctions: Events in which large numbers of species go extinct in a short period.

Chapter 26: Bacteria and Archaea

Characteristics of Prokaryotes

Bacteria and Archaea are single-celled organisms without a nucleus.

• Bacteria vs. Archaea: Differ in cell wall composition, membrane lipids, and genetic machinery.

• Gram-positive bacteria: Thick peptidoglycan cell wall; stain purple.

• Gram-negative bacteria: Thin peptidoglycan layer and outer membrane; stain pink.

• Human microbiome: The collection of microbes living in and on the human body.

• Koch’s postulates: Criteria to establish a causative relationship between a microbe and a disease.

• Antibiotics: Chemicals that kill or inhibit bacteria.

Chapter 27: Diversification of Eukaryotes

Protists and Endosymbiotic Theory

Protists are a diverse group of eukaryotes; not a single evolutionary group.

• Endosymbiotic theory: Mitochondria and chloroplasts originated from bacteria engulfed by ancestral eukaryotes.

• Evidence: Mitochondria and chloroplasts have their own DNA and double membranes.

Chapter 28: Green Algae and Land Plants

Adaptations to Land

Plants evolved adaptations to survive on land.

• Cuticle: Waxy layer that prevents water loss.

• Stomata: Pores that regulate gas exchange.

• Alternation of generations: Life cycle alternates between multicellular haploid and diploid stages.

• Pollen and seeds: Allow reproduction without water and protect embryos.

Chapter 29: Fungi

Fungal Nutrition and Relationships

Fungi obtain nutrients by external digestion and absorption.

• External digestion: Secrete enzymes to break down food outside their bodies.

• Fungi are more closely related to animals than plants.

• Fungal infections are difficult to treat due to similarities with animal cells.

Chapter 30: An Introduction to Animals

Animal Characteristics and Evolution

Animals share certain characteristics and have diverse body plans.

• Shared traits: Multicellularity, heterotrophy, movement, specialized tissues.

• Symmetry: Radial or bilateral body plans.

• Cephalization: Development of a head region with sensory organs.

• Major trends include increased complexity and specialization.

Chapter 31: Protostome Animals

Protostomes vs. Deuterostomes

Protostomes and deuterostomes differ in embryonic development.

• Protostomes: Mouth develops before anus; includes arthropods, mollusks, annelids.

• Insects are highly diverse and successful due to adaptations like wings and metamorphosis.

Chapter 32: Deuterostome Animals

Deuterostome Characteristics and Evolution

Deuterostomes include chordates and echinoderms.

• Deuterostomes: Anus develops before mouth.

• Chordate characteristics: Notochord, dorsal nerve cord, pharyngeal slits, post-anal tail.

• Major vertebrate adaptations: jaws, limbs, amniotic egg.

• Adaptations for life on land: lungs, waterproof skin, internal fertilization.

• Human evolution: Trends include bipedalism, larger brains.

• Out of Africa hypothesis: Modern humans originated in Africa and spread worldwide.