Biological Evolution and Genetics: Key Concepts and Processes

Biological Fitness

How much an individual's genotype is represented in the next generation; depends on survival and reproduction, not physical strength.

Adaptation

Trait that increases fitness in an individual; also the process of a population becoming better suited to its environment.

Maladaptive

Trait or behavior that reduces fitness or is poorly suited to the environment.

Melanin

Skin pigment that protects DNA from UV; more melanin → darker skin, protects folate; less melanin → lighter skin, allows Vitamin D synthesis.

MC1R gene

Controls skin pigmentation; strong selection in high UV areas to protect folate.

Race (biology)

Social construct, not a strict biological category; humans show gradual genetic variation.

Evolution

Change in frequency of a genetic trait (allele/genotype) in a population over time.

Neutral mutation

No effect on fitness.

Deleterious mutation

Decreases fitness.

Population

Group of organisms of the same species in an area.

Gene pool

All alleles in a population.

Genotype vs. Phenotype

Genotype = genetic makeup; phenotype = observable traits.

Mutation

Random DNA change; can be neutral, beneficial, or harmful.

Gene flow

Movement of alleles between populations.

Genetic drift

Random change in allele frequencies, stronger in small populations.

Natural selection

Traits increasing fitness become more common.

Stabilizing selection

Favors average phenotype.

Directional selection

Favors one extreme.

Disruptive selection

Favors both extremes.

Hardy-Weinberg Equilibrium

Baseline model to test if populations are evolving; p + q = 1; p², 2pq, q² = genotype frequencies.

Speciation

One species splits into two; requires reduced gene flow.

Allopatric speciation

Geographic separation; dispersal or vicariance.

Sympatric speciation

Same area; driven by disruptive selection or polyploidy.

Pre-zygotic barrier

Prevents mating/fertilization.

Post-zygotic barrier

Hybrid forms but is sterile or inviable.

Systematics

Study of diversity and classification.

Taxonomy

Naming and ranking organisms.

Phylogenetics

Study of evolutionary history.

Lineage

Ancestor-descendant series.

Prokaryotes

No nucleus, circular chromosomes, no organelles.

Eukaryotes

Nucleus, linear chromosomes, organelles.

Horizontal gene transfer (HGT)

Movement of genes between unrelated bacteria.

Endosymbiosis

Mitochondria and chloroplasts originated from engulfed bacteria.

Synapomorphy

Shared derived trait at the base of a clade.

Totipotent

Cell that can become any type of cell.

Blastula

Hollow ball of cells in early animal development.

Germ layers

Ectoderm, mesoderm, endoderm.

Mycelium

Fungal body made of hyphae.

Apical meristems

Plant growth from totipotent cells.

Cuticle

Waxy coating on plants to reduce water loss.

Alternation of generations

Plants alternate haploid gametophyte and diploid sporophyte.

Xylem

Transports water/minerals in plants.

Phloem

Transports sugars in plants.

Annuals

Complete life cycle <1 year.

Perennials

Live multiple years; often woody or evergreen.

Photoautotroph

Uses light for energy, CO₂ for carbon.

Chemoautotroph

Uses inorganic chemicals for energy, CO₂ for carbon.

Photoheterotroph

Uses light for energy, organic compounds for carbon.

Chemoheterotroph

Uses organic compounds for energy and carbon.

Mitosis

Produces 2 identical cells; growth, repair, asexual reproduction; occurs in somatic cells.

Meiosis

Produces 4 haploid cells; genetically unique; sexual reproduction; occurs in germ cells.

Asexual reproduction

Offspring are clones; fast; no mate required; low variation.

Sexual reproduction

Meiosis + fertilization; high variation; slower; requires mate.

Genetic variation sources

Crossing over, independent assortment, fertilization, outcrossing.

Dispersal importance

Reduces competition, allows colonization.

Animals

Haploid gametes via meiosis; diploid zygote.

Plants

Gametophyte (1n) produces gametes via mitosis; sporophyte (2n) develops after fertilization.

Fungi

Mostly haploid; plasmogamy → heterokaryotic → karyogamy → diploid → meiosis → spores.

Bryophytes

Non-vascular, gametophyte dominant, need water for sperm.

Lycophytes

Small vascular plants, microphylls.

Ferns & allies

Vascular, seedless, sporophyte dominant.

Gymnosperms

Seeds 'naked,' cones; female gametophyte nourishes embryo.

Angiosperms

Flowers, fruits, double fertilization; outcrossing increases variation.

Annuals vs. Perennials

Short-lived vs. long-lived survival strategies.

Angiosperm success factors

Protected ovules, animal pollination, fruits for dispersal, double fertilization, ecological range.

Meiosis produces...?

4 haploid cells, genetically different from each other and parent.

Function of mitosis?

Growth and repair in multicellular organisms.

Outcrossing vs. selfing?

Outcrossing → more genetic variation; selfing → less variation.

Why is skin darker near equator?

High UV → melanin protects folate; natural selection favors higher melanin.

What is stabilizing selection?

Favors intermediate phenotype.

What is directional selection?

Favors one extreme phenotype.

What is adaptive radiation?

Rapid speciation into new ecological niches after extinction events.

Key synapomorphy of animals?

Blastula stage during development.

Key synapomorphy of fungi?

Chitin in cell walls; absorptive nutrition.

Key synapomorphy of plants?

Alternation of generations, apical meristems, cuticle.

Hardy-Weinberg: if p = 0.6, q = 0.4 → expected heterozygotes?

2pq = 2 × 0.6 × 0.4 = 0.48 (48%).

Example of natural selection in humans?

Lactose tolerance, disease resistance, skin color variation.

Pre-zygotic vs. post-zygotic barriers?

Pre → prevent mating/fertilization; post → hybrids sterile/inviable.

Horizontal gene transfer?

Movement of genes between unrelated bacteria; speeds adaptation.

Endosymbiosis evidence?

Mitochondria/chloroplasts have own DNA, double membranes, replicate independently.

Fungal reproduction?

Plasmogamy → heterokaryotic hypha → karyogamy → meiosis → haploid spores.

Difference between annuals and perennials?

Annuals <1 year, fast reproduction; perennials >1 year, often woody or evergreen.

Bryophytes require what for fertilization?

Water for flagellated sperm.

Seeds components?

Seed coat = parent sporophyte (2n), Embryo = new sporophyte (2n), Food = female gametophyte (1n, gymnosperms) or endosperm (3n, angiosperms).

Trade-off of melanin

Protects folate but high melanin reduces Vitamin D synthesis.

Non-human pigmentation example

Dragonflies — darker wings → heat in cool climates; lighter wings → better in hot climates.

UV & melanin correlation

Higher UV → higher melanin.

Selective pressure for MC1R alleles

In high UV areas comes from folate protection, not mainly skin cancer.

Antibiotic resistance

Evolution in action, driven by mutation + selection.

Misuse of antibiotics

Increases selective pressure → speeds resistance.

Differential reproduction

Required for natural selection, even without limited resources.

MEGA-plate experiment

Shows real-time evolution of bacteria.

Viruses vs. bacteria

Antibiotics don't work on viruses.

Horizontal gene transfer

Spreads resistance alleles.

Ways to slow resistance

Reduce selective pressure (e.g., avoid unnecessary antibiotics).

Barriers to gene flow

Behavioral, temporal, mechanical (pre-zygotic).

Lineage diagrams / phylogenetic trees

Direction of time = bottom → top or left → right.

Taxonomic ranks mnemonic

Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species.

Timeline of life

Earth forms, prokaryotes, oxygen rise, eukaryotes, multicellular eukaryotes, animals, land plants, primates, humans.

Nutritional categories

Photoautotrophs, chemoautotrophs, photoheterotrophs, chemoheterotrophs.