Comprehensive Study Guide: Genetics, Evolution, and Ecology (BIOL 1307)

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Reproduction

Asexual vs. Sexual Reproduction

Reproduction is the biological process by which new individual organisms are produced. There are two main modes: asexual and sexual reproduction, each with distinct genetic and evolutionary implications.

Asexual Reproduction: Involves a single parent and produces offspring that are genetically identical to the parent (clones). Common in prokaryotes, some protists, plants, and a few animals.
Sexual Reproduction: Involves two parents and the fusion of gametes (sperm and egg), resulting in genetically diverse offspring. Found in most animals and plants.

Feature	Asexual	Sexual
Parents	1	2
Genetic Variation	Low	High
Offspring Similarity	Identical	Different
Speed	Fast	Slower
Environment	Stable	Changing

Advantages of Asexual Reproduction: Rapid population increase, no need for a mate, efficient in stable environments.
Disadvantages: Little/no genetic variation, population vulnerable to disease or environmental change.
Advantages of Sexual Reproduction: High genetic variation, better adaptation to changing environments.
Disadvantages: Slower, requires finding a mate, more energy required.

Mechanisms of Asexual Reproduction

Prokaryotes: Binary fission (rapid, produces clones, no nucleus involved).
Protists: Binary fission, multiple fission, budding, fragmentation.
Plants: Vegetative reproduction (runners, rhizomes, tubers, bulbs).
Animals: Budding, fragmentation/regeneration, parthenogenesis.

Group	Main Mechanism	Key Feature
Prokaryotes	Binary fission	Fast, simple
Protists	Multiple methods	Very diverse
Plants	Vegetative reproduction	Specialized structures
Animals	Budding, fragmentation, parthenogenesis	Less common

Mechanisms of Sexual Reproduction

Protists: Gamete production (usually by meiosis), fertilization (external or conjugation), minimal embryo protection.
Plants: Alternation of generations (sporophyte produces spores by meiosis, gametophyte produces gametes by mitosis), fertilization (water or pollen), embryo protection (seeds or tissues).
Animals: Gamete production by meiosis, fertilization (external or internal), embryo protection (eggs or internal development).

Feature	Protists	Plants	Animals
Gametes	Meiosis	Mitosis (gametophyte)	Meiosis
Spores	Sometimes	Yes (key stage)	No
Fertilization	Mostly external	Water or pollen	External or internal
Embryo protection	Minimal	Seeds/tissues	Eggs or body

Heredity and Meiosis

Phases and Events of Meiosis

Meiosis is a specialized type of cell division that reduces the chromosome number by half, producing four haploid cells (gametes or spores). It consists of two sequential divisions: Meiosis I and Meiosis II.

Meiosis I

Goal: Separate homologous chromosomes.
Starting cell: Diploid (2n).
Phases:
- Prophase I: Chromosomes condense, homologous chromosomes pair (tetrads), crossing over occurs (genetic variation), nuclear envelope breaks down, spindle forms.
- Metaphase I: Tetrads align at the cell equator, orientation is random (independent assortment).
- Anaphase I: Homologous chromosomes separate, sister chromatids remain together.
- Telophase I & Cytokinesis: Two haploid cells form, each with one chromosome from each pair.
Ploidy after Meiosis I: Haploid (n), each chromosome has two sister chromatids.

Meiosis II

Goal: Separate sister chromatids.
Phases:
- Prophase II: Chromosomes condense, spindle forms.
- Metaphase II: Chromosomes align single file at the equator.
- Anaphase II: Sister chromatids separate.
- Telophase II & Cytokinesis: Four haploid cells form, each with one chromatid per chromosome.
Ploidy after Meiosis II: Haploid (n), each chromosome has one chromatid.

Phase	Key Event
Prophase I	Crossing over + pairing
Metaphase I	Tetrads align
Anaphase I	Homologs separate
Telophase I	2 haploid cells form
Prophase II	Spindle forms
Metaphase II	Chromosomes line up single file
Anaphase II	Sister chromatids separate
Telophase II	4 haploid cells form

Crossing Over: Exchange of DNA segments between homologous chromosomes during Prophase I, increasing genetic variation. Occurs at chiasmata between non-sister chromatids.
Independent Assortment: Random orientation of tetrads during Metaphase I, leading to genetic diversity.

Genetic Terms and Inheritance

Gene: Segment of DNA coding for a specific trait or function.
Locus: Physical location of a gene on a chromosome.
Allele: Different version of a gene. Diploid organisms have up to two alleles per locus; populations can have many.
Dominant/Recessive: Dominant alleles mask recessive alleles in heterozygotes.
Wild-type/Mutant: Wild-type is the most common allele; mutant is a variant.
Sex-linked: Traits associated with genes on sex chromosomes (often X-linked).

Punnett Squares and Pedigrees

Punnett Square: Tool to predict genotype and phenotype ratios from parental crosses (autosomal and X-linked traits).
Pedigree Analysis: Used to determine inheritance patterns (dominant, recessive, sex-linked).

DNA Structure and Function

Complementary Base Pairing and Antiparallel Strands

Base Pairing: Adenine (A) pairs with Thymine (T); Cytosine (C) pairs with Guanine (G).
Antiparallel: DNA strands run in opposite directions: one 5'→3', the other 3'→5'.

DNA Replication

Semiconservative: Each new DNA molecule has one old and one new strand.
Key Enzymes:
- Helicase: Unwinds DNA.
- SSBPs: Stabilize single strands.
- Primase: Adds RNA primers.
- DNA Polymerase: Synthesizes new DNA (5'→3').
- DNA Ligase: Joins Okazaki fragments on lagging strand.
Leading Strand: Synthesized continuously toward replication fork.
Lagging Strand: Synthesized discontinuously away from fork in Okazaki fragments.

Gene Expression: Transcription and Translation

Transcription

Purpose: Copy DNA information into mRNA.
Location: Nucleus (eukaryotes), cytoplasm (prokaryotes).
Key Steps:
- Initiation: RNA polymerase binds promoter, DNA unwinds.
- Elongation: RNA polymerase synthesizes mRNA (5'→3').
- Termination: RNA polymerase reaches terminator, mRNA released.
mRNA Processing (Eukaryotes): Introns removed, exons joined.

Translation

Purpose: Use mRNA to build proteins at ribosomes in cytoplasm.
Key Molecules: mRNA, ribosome (rRNA + proteins), tRNA (with anticodon), amino acids.
Key Steps:
- Initiation: Ribosome binds mRNA at 5' end, finds start codon (AUG).
- Elongation: tRNAs bring amino acids, peptide bonds form, chain grows.
- Termination: Stop codon reached, protein released.

Genetic Code

Codon: Sequence of 3 RNA bases coding for one amino acid or stop signal.
Start Codon: AUG (Methionine).
Stop Codons: UAA, UAG, UGA.
Number of Codons: codons for 20 amino acids.

Transcription Factors and Gene Regulation

Transcription Factors: Proteins that regulate gene expression by binding DNA.
Activators: Increase gene expression.
Repressors: Decrease gene expression.
Cell Specialization: Different transcription factors activate different genes in different cell types (e.g., muscle vs. neuron).

Evolution and Natural Selection

Conditions for Natural Selection

Variation: Individuals differ in traits.
Heritability: Traits must be genetically inherited.
Selection: Individuals with advantageous traits survive and reproduce more, increasing those alleles in the population.

Adaptive vs. Random Evolution

Adaptive Evolution: Driven by natural selection, increases beneficial traits.
Random Evolution: Driven by chance (genetic drift, mutation), not necessarily beneficial.

Types of Random Evolution

Genetic Drift: Random changes in allele frequencies, strongest in small populations.
Founder Effect: New population started by a few individuals.
Bottleneck Effect: Population size drastically reduced by disaster.

Modes of Natural Selection

Stabilizing Selection: Favors average phenotype (e.g., human birth weight).
Directional Selection: Favors one extreme phenotype (e.g., longer beaks).
Disruptive Selection: Favors both extremes, selects against average (e.g., very small and very large seeds).

Phylogenetics

Phylogenetic Trees

Common Ancestor: Species sharing a branch point share a common ancestor.
Tree Comparison: Trees are equivalent if relationships are the same, even if branches are rotated.
Clade: Group of descendants from a single ancestor.
Parsimony: Simplest tree with fewest evolutionary changes is preferred.

Ecology

Patterns of Dispersion

Clumped: Individuals grouped together (e.g., herds).
Uniform: Evenly spaced (e.g., territorial birds).
Random: No predictable pattern (e.g., wind-dispersed plants).

Population Growth

Exponential Growth: Unlimited resources, J-shaped curve.
- Equation:
Logistic Growth: Limited resources, S-shaped curve.
- Equation:
Density-dependent factors: Effects increase with population density (e.g., disease).
Density-independent factors: Affect populations regardless of density (e.g., natural disasters).

Community Diversity

Species Richness: Number of species.
Species Evenness: Distribution of individuals among species.
Shannon Index: Measures biodiversity.
- Formula:

Energy Flow and Productivity

First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.
Biogeochemical Cycles: Movement of elements (carbon, nitrogen, water) through ecosystems.
Productivity Pyramid: Energy transfer between trophic levels (~10% efficiency).

Trophic Level	Example
Producers	Plants
Primary Consumers	Herbivores
Secondary Consumers	Carnivores
Tertiary Consumers	Top predators

Key Vocabulary

Gene Pool: All alleles in a population.
Locus: Specific position of a gene on a chromosome.
Gene: DNA sequence specifying a protein.
Allele: Different version of a gene.
Stabilizing Selection: Intermediate phenotype favored.
Disruptive Selection: Both extremes favored.
Directional Selection: One extreme favored.
Genetic Drift: Random allele frequency changes.
Founder Effect: New population from few individuals.
Bottleneck Effect: Population size drastically reduced.
Gene Flow: Movement of alleles between populations.
Sexual Dimorphism: Differences between sexes due to sexual selection.
Parsimony: Simplest evolutionary tree preferred.
Sister Taxa: Closest relatives on a phylogenetic tree.
Outgroup: Lineage outside the group of interest.
Shared Ancestral Character: Trait from common ancestor.
Shared Derived Character: New trait unique to a clade.
Clade: Group of organisms from a single ancestor.
Cyanobacteria: Photosynthetic bacteria producing O2.
Endosymbiosis: One organism lives inside another (e.g., mitochondria).
Archaea: Domain of prokaryotes, often extremophiles.
Biotic: Living components of environment.
Abiotic: Non-living physical/chemical factors.
Niche: Role of an organism in its environment.
Trophic Level: Position in a food chain.
Population: Group of same species in an area.
Ecosystem: Community plus abiotic environment.
Clumped/Uniform/Random Dispersion: Patterns of spatial distribution.
Quadrat/Transect/Mark-Recapture: Methods for estimating population size.
Carrying Capacity (K): Maximum population environment can support.
Birth Rate (b)/Death Rate (m): Number of births/deaths per population over time.
Microevolution: Change in allele frequency over generations.
Genetic Variation: Differences in genetic makeup among individuals.
Taxon: Named unit at any level of classification.
Phylogeny: Evolutionary relationships among organisms.
Homoplasy: Similar traits due to convergent evolution, not common ancestry.

Additional info: For full mastery, students should practice drawing and labeling stages of meiosis and mitosis, solve Punnett square problems, and interpret population growth graphs and phylogenetic trees.