Comprehensive Biology: Genetics, Cell Cycle, Evolution, and Taxonomy

Heuristics

Learn by doing; practical rather than perfect.

Consilience

Fit discoveries into a 'grand scheme' of universal principles.

Builds on previous knowledge

Science grows cumulatively.

Social

Findings are shared and reviewed by others.

Stimulates further discovery

Leads to new questions and research.

Economy

Uses the simplest explanation that fits the evidence.

Gene

A segment of DNA that codes for a trait.

Allele

A version of a gene that can produce variation in that trait.

Genetic trait

A characteristic of an individual determined by genes, the environment, or both.

Chromosome

A DNA molecule with associated proteins, carrying many genes.

Locus

The fixed location of a gene on a chromosome.

Homologous chromosomes

A matching pair (one from each parent) carrying the same genes, possibly different alleles.

Centromere

The 'waist' of a duplicated chromosome where sister chromatids are joined and spindle fibers attach.

Sister chromatids

Identical copies of a chromosome joined at a centromere after DNA replication.

Ploidy

The number of complete sets of chromosomes in a cell (haploid = 1, diploid = 2, triploid = 3, etc.).

Cell cycle

The ordered series of events from one cell division to the next (interphase + mitotic phase).

Interphase

Interphase happens before mitosis and it's the longest part of the cell cycle. It includes three phases: G1, S, G2.

G1

Cell grows and makes proteins/organelles.

S

DNA is replicated (each chromosome copied).

G2

Cell continues growing and prepares for division.

Mitotic phase (M phase)

Includes mitosis and cytokinesis.

Mitosis

Nuclear division making two genetically identical diploid cells.

Stages of mitosis (PMAT)

Prophase, Metaphase, Anaphase, Telophase.

Prophase

Chromosomes condense; spindle forms; nuclear envelope breaks down.

Metaphase

Chromosomes align along the cell's equator; spindle fibers attach at centromeres.

Anaphase

Centromeres split; spindle fibers pull sister chromatids to opposite poles.

Telophase

Chromatids arrive at poles, nuclei reform, chromosomes relax; cytokinesis often follows.

Meiosis

Two-part cell division producing four genetically unique cells with half the parent ploidy.

Meiosis I

Homologous chromosomes pair, cross over, and separate.

Meiosis II

Sister chromatids separate, like mitosis.

Evolution (concise)

Heritable change in allele frequencies in a population over generations.

Microevolution

Small, observable shifts in allele frequencies.

Macroevolution

Large-scale change leading to new species or higher groups over long time spans.

Population

All individuals of a species in the same area at the same time.

Species (biological)

A group of organisms that can interbreed and produce viable offspring.

Natural selection

Differential survival and reproduction based on heritable traits, causing adaptive change.

Adaptation

A heritable trait that increases survival or reproduction in the current environment.

Fitness (evolutionary)

The number of viable offspring an individual contributes to the next generation compared to others.

Genetic drift

Random changes in allele frequency, strongest in small populations.

Bottleneck effect

Loss of genetic variation after a sharp population size reduction.

Founder effect

Allele frequency shift when a few individuals establish a new population.

Gene flow

Movement of alleles between populations via migration or reproduction.

Mutation

Random DNA change creating new alleles.

Sexual selection

A type of natural selection favoring traits that improve mating success.

Law of segregation (Mendel)

The two alleles for a gene separate during gamete formation.

Taxonomic hierarchy

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

Binomial nomenclature

Two-part scientific name for species (Genus + species, ex: Felis catus).

Phylogeny

A branching diagram showing hypothesized evolutionary relationships.

Law of parsimony

The simplest explanation or tree requiring the fewest evolutionary changes is most likely correct.

Biology

The study of living organisms and the processes of life.

Characteristics of life

Order, reproduction, growth/development, energy use, response to environment, homeostasis, adaptation.

Scientific theory

A well-supported structure of ideas explaining and linking observations.

Scientific fact

A statement so well-confirmed it would be unreasonable to doubt (yet still open to new evidence).

Science is tentative

Explanations can change with new data.

Qualities of Good Science (E.O. Wilson)

Heuristics

Consilience

Builds on previous knowledge

Social

Stimulates further discovery

Economy

Evolutionary tree

The diagram itself that visually represents that phylogeny, showing branching patterns of descent.

Independent Variable (IV)

The factor you purposely change in an experiment.

Dependent Variable (DV)

The factor you measure to see how it responds to the IV.

Bar graph

Use when comparing categories or groups (IV = discrete).

Line graph

Use when showing trends over time or a continuous IV.

Scatter plot

Use for relationships between two continuous variables.

Allopatric speciation

Formation of a new species after populations become geographically isolated.

Sympatric speciation

Formation of a new species without physical separation, usually through genetic or ecological barriers.

Law of segregation

Two alleles for a gene separate during gamete formation.

Law of independent assortment

Alleles of different genes assort independently during gamete formation (if on different chromosomes).

Biological species concept

A species is a group of organisms that can interbreed and produce viable, fertile offspring.

Morphological species concept

A species is defined by shared physical features (used when reproductive data isn't available).

Genetic species concept

A species is defined by similarity or distinctiveness in DNA sequences.

Characteristics of Life

Highly ordered structure

Reproduction

Growth and development

Energy utilization (metabolism)

Response to the environment

Homeostasis (regulation)

Evolutionary adaptation

Outgroup

A species (or group) that is closely related to, but not part of, the group you're studying. It helps you figure out which traits are old (ancestral) and which ones are new (derived) on a phylogenetic tree.

Shared derived characteristic

characters shared by all in your ingroup (unlesslater lost)

Shared ancestral characteristic

A new characteristic that evolved within your ingroup

Divergent Evolution

Closely related species look really different

convergent evolution

Similar traits evolve independently in distantly related species

Homologies (homologous traits)

Traits that are similar because they were inherited from a common ancestor — they may look different now but have the same evolutionary origin

Analogies (analogous traits)

Traits that look or function alike but evolved independently, not from a shared ancestor (often due to similar environments)

Replicates

Sample size