Biology: Taxonomy, Evolution, and Genetics Key Concepts

Taxonomy

The science of classifying and naming living organisms.

Carl Linnaeus

Father of modern taxonomy; created the binomial nomenclature system still used today.

Binomial nomenclature

Two-part scientific naming system: Genus (capitalized) + species (lowercase), written in italics — e.g., Homo sapiens.

Taxonomy hierarchy

King Philip Came Over For Good Soup → Kingdom, Phylum, Class, Order, Family, Genus, Species (broadest → most specific).

Species

The most specific classification level; organisms that can breed and produce FERTILE offspring belong to the same species.

Dichotomous key

A tool that identifies organisms through a series of paired, either/or descriptors; used to find the scientific name of an unknown organism.

Genus name

Always capitalized.

Species name

Always lowercase.

Both words

Italicized when typed (underlined when handwritten).

Correct example of binomial nomenclature

Homo sapiens.

Wrong examples of binomial nomenclature

Homo sapiens, homo sapiens, HOMO SAPIENS, Homo Sapiens.

Organism

A single living individual.

Population

All individuals of the SAME species living in the same area at the same time.

Community

All populations of DIFFERENT species living together in the same area (biotic only).

Ecosystem

All living (biotic) AND non-living (abiotic) components interacting in an area — the most complete level.

Biosphere

All ecosystems on Earth combined — the most complex/broadest level of organization.

Biotic factors

Living components of an ecosystem (plants, animals, bacteria, fungi, etc.).

Abiotic factors

Non-living components: sunlight, temperature, water, soil type, pH, wind.

Producer

Organism that makes its own food via photosynthesis (usually a plant or algae); the base of every food web.

Consumer

Organism that eats other organisms for energy (herbivores, carnivores, omnivores).

Decomposer

Organisms (bacteria, fungi) that break down dead matter and recycle nutrients back into the ecosystem.

Food web / chain

Shows the flow of energy from one organism to the next; arrows point in the direction energy travels (prey → predator).

Trophic levels

Feeding levels: Producers → Primary consumers → Secondary consumers → Tertiary consumers.

10% Rule

Only ~10% of energy is transferred to the next trophic level; ~90% is lost as heat through metabolic processes.

Energy pyramid

Visual showing energy decreasing at each level — producers have the MOST energy, top predators have the LEAST.

Carbon cycle

CO₂ removed from atmosphere by PHOTOSYNTHESIS; returned by cellular respiration, decomposition, and combustion.

Nitrogen fixation

Bacteria convert N₂ gas → ammonia/nitrates that plants can use. Without this, plants cannot access atmospheric nitrogen.

Denitrification

Bacteria convert nitrates → N₂ gas, returning nitrogen to the atmosphere.

Nitrogen cycle key organisms

Bacteria are responsible for both nitrogen fixation and denitrification.

Natural selection

Process by which organisms with beneficial heritable traits survive and reproduce more successfully; requires genetic variation, heritability, and differential survival.

Adaptation

A heritable trait that improves an organism's fitness (survival/reproduction) in its environment.

Genetic variation

Differences in DNA among individuals in a population; PRIMARY source = random mutations.

Genetic diversity

Increases the likelihood that SOME individuals will survive disease or environmental change — critical for population resilience.

Coevolution

Two or more species mutually influence each other's evolution over time (e.g., flowering plant & its pollinator).

Convergent evolution

Unrelated species independently evolve similar traits due to similar environments — produces ANALOGOUS structures.

Divergent evolution

One ancestral species splits into multiple species with different traits — produces HOMOLOGOUS structures; also called adaptive radiation.

Homologous structures

Same underlying anatomy/embryological origin but different functions — evidence of COMMON ANCESTOR (divergent evolution). Ex: human arm, bat wing, whale flipper.

Analogous structures

Same FUNCTION but different evolutionary origin — evidence of convergent evolution. Ex: bird wing and insect wing.

Vestigial structures

Body parts with little/no current function that were useful in ancestors. Ex: human coccyx (tailbone), whale pelvis.

Fossil record

Preserved remains of past organisms; shows transitional forms and timing of species divergence.

Molecular/DNA evidence

Species that share more DNA sequences are more closely related; fewer nucleotide differences = more recent common ancestor.

Geographic isolation

Physical barrier separates populations → allopatric speciation. Ex: mountain range, river, ocean.

Temporal isolation

Populations breed at different times (seasons, times of day). Ex: one bird sings at dawn, another at dusk.

Behavioral isolation

Different courtship rituals, calls, or mating behaviors prevent interbreeding.

Mechanical isolation

Structural differences in reproductive organs prevent mating.

Gene

A segment of DNA that serves as the blueprint/instructions for making a specific protein.

Allele

Different versions of the same gene (e.g., B = black, b = white).

Genotype

The actual allele combination an organism carries — written as letters (BB, Bb, bb).

Phenotype

The observable, physical expression of the genotype (e.g., black coat, blue eyes, round seeds).

Dominant allele

An allele that is expressed whenever it is present (even in one copy); written as a capital letter.

Recessive allele

An allele that is only expressed when TWO copies are present (homozygous recessive); written lowercase.

Homozygous

Two identical alleles (BB or bb).

Heterozygous

Two different alleles (Bb).

Dominance

One allele completely masks the other. Heterozygote looks the same as the dominant homozygote.

Incomplete dominance

Neither allele is fully dominant; heterozygote shows a BLENDED phenotype (e.g., red × white = pink).

Codominance

Both alleles are fully expressed simultaneously in the heterozygote (e.g., red + white patches, not pink).

Punnett Squares

Write one parent's alleles across the top, the other parent's down the side. Fill in each box by combining the allele from its row and column.

Genotypic ratio

1 BB : 2 Bb : 1 bb

Phenotypic ratio

3 dominant : 1 recessive

DNA

Double-stranded helix; contains A, T, G, C; found mainly in the nucleus; stores genetic information across generations.

RNA

Single-stranded; contains A, U (uracil — NOT thymine), G, C; involved in protein synthesis; found in nucleus AND cytoplasm.

Chargaff's Rules

A pairs with T (DNA) or U (RNA); G pairs with C. If a DNA sample is 28% T → it is also 28% A; G+C = 44%, so G = C = 22%.

DNA replication

Semi-conservative: each new double helix has ONE original strand + ONE new strand. Occurs during S phase of interphase.

Transcription

DNA → mRNA; occurs in the nucleus. DNA template strand is read 3'→5'; mRNA is synthesized 5'→3'.

Translation

mRNA → protein; occurs at ribosomes in the cytoplasm. Each 3-base codon codes for one amino acid.

Codon

A 3-nucleotide sequence on mRNA that specifies an amino acid (or start/stop signal).

Mutation

Any change in the DNA sequence.

Point mutation

Substitution of ONE nucleotide for another. May be silent (no amino acid change) or missense (changes one amino acid).

Silent mutation

Nucleotide changes but, due to codon redundancy, the same amino acid is produced — no effect on protein.

Frameshift mutation

Insertion or deletion of nucleotide(s) shifts the entire reading frame downstream — usually severe, disrupts all codons after the mutation.

Insertion

One or more nucleotides added to the sequence → frameshift.

Deletion

One or more nucleotides removed from the sequence → frameshift.

Somatic mutation

Occurs in body (somatic) cells; affects only that individual; CANNOT be inherited by offspring.

Germline mutation

Occurs in gametes (egg/sperm); CAN be passed to offspring — more significant for evolution and hereditary disease.

Interphase

The phase where cells spend most of their time — growing (G1), replicating DNA (S), and preparing for division (G2).

Mitosis

Division of somatic (body) cells → 2 genetically IDENTICAL diploid daughter cells.

Meiosis

Division of reproductive cells (gonads) → 4 genetically UNIQUE haploid gametes (sperm/egg).

Somatic cells

All body cells EXCEPT gametes. These undergo mitosis.

Gametes

Egg and sperm cells — produced by meiosis.

Diploid (2n)

Contains two sets of chromosomes (one from each parent). Normal body cells are diploid.

Haploid (n)

Contains one set of chromosomes. Gametes are haploid.

Abiotic

Non-living environmental factors.

Biotic

Living components of an ecosystem.

Primary consumer

Eats producers directly (herbivore).

Photosynthesis

Removes CO₂ from atmosphere; stores energy in glucose.

Dominant

Allele expressed when present in one copy.

Recessive

Allele expressed only in homozygous state.