Comprehensive Biology Study Guide

Biological Organization Levels (Smallest to Largest)

Atom → molecule → macromolecule → organelle → cell → tissue → organ → organ system → organism → population → community → ecosystem → biosphere.

Population vs. Community

A population comprises individuals of one species in an area; a community includes populations of multiple species.

Community vs. Ecosystem

A community consists of living organisms; an ecosystem includes the community plus its nonliving environment.

Biological Species Concept

Groups organisms that interbreed naturally and produce viable, fertile offspring.

Cell Theory Principles

All living organisms consist of cells; the cell is the basic unit of life; cells arise from preexisting cells.

Sister Chromatids vs. Homologous Chromosomes

Sister chromatids are identical copies of one duplicated chromosome; homologous chromosomes are maternal/paternal pairs with same genes.

Stages of Interphase

G1 (growth/normal functions), S (DNA replication), G2 (preparation for division/checking DNA).

Mitosis Stages (PMAT)

Prophase (condense), Metaphase (align in middle), Anaphase (sister chromatids separate), Telophase (two nuclei form).

Cytokinesis: Animals vs. Plants

Animal cells divide via a cleavage furrow; plant cells form a cell plate.

Mitosis Outcome

Produces two genetically identical diploid daughter cells from one diploid parent cell.

G1 Cell-Cycle Checkpoint

Evaluates cell size, nutrients, growth signals, and DNA integrity; non-dividing cells enter G0.

Benign vs. Malignant Tumors

Benign tumors do not invade surrounding tissue; malignant tumors invade tissues and can metastasize.

Meiosis I Key Event

Separates homologous chromosomes, reducing chromosome number by half.

Meiosis II Key Event

Separates sister chromatids, yielding four haploid products.

Human Chromosome Count After Replication (Before Meiosis I)

46 chromosomes and 92 chromatids per cell.

Human Chromosome Count After Meiosis I

23 duplicated chromosomes and 46 chromatids per cell.

Human Chromosome Count After Meiosis II

23 single chromosomes and 23 chromatids per cell.

Three Sources of Genetic Variation in Sexual Reproduction

Independent assortment, crossing over, and random fertilization.

Origin of New Alleles

Mutation is the only process that creates brand-new alleles; sexual reproduction reshuffles existing ones.

Nondisjunction

Failure of homologous chromosomes or sister chromatids to separate properly during meiosis.

Mendel's Law of Segregation

An individual's two alleles for a gene separate during gamete formation.

Mendel's Law of Independent Assortment

Alleles of unlinked genes assort independently into gametes.

Monohybrid Cross (Pp × Pp) Ratios

Genotypic ratio 1 PP : 2 Pp : 1 pp; Phenotypic ratio 3 dominant : 1 recessive.

Purpose of a Test Cross

Crosses an unknown dominant phenotype individual with a homozygous recessive (bb) individual to determine genotype.

Dihybrid Cross (BbDd × BbDd) Phenotypic Ratio

9 dominant/dominant : 3 dominant/recessive : 3 recessive/dominant : 1 recessive/recessive.

Incomplete Dominance vs. Codominance

Incomplete dominance yields an intermediate phenotype; codominance expresses both alleles distinctly simultaneously.

Pleiotropy vs. Polygenic Inheritance

Pleiotropy: one gene affects multiple traits. Polygenic: multiple genes influence a single trait.

X-Linked Recessive Inheritance Pattern

Traits affect XY individuals more frequently; fathers pass Y chromosomes to sons, not X-linked alleles.

Evolution vs. Natural Selection

Evolution is genetic change in a population over generations; natural selection is a mechanism driving that change.

Relative Fitness

An individual's reproductive contribution to the next generation relative to other individuals in the population.

Lamarckism vs. Darwinian Selection

Lamarck proposed inheritance of acquired traits; Darwin proposed natural selection acting on pre-existing heritable variation.

Taxonomic Hierarchy Order

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

Five Lines of Evolutionary Evidence

Fossil record, biogeography, comparative anatomy, comparative embryology, and molecular biology.

Homologous vs. Analogous Structures

Homologous structures share common ancestry despite different functions; analogous structures share function due to convergent evolution.

Vestigial Structures

Reduced remnants of ancestral features that may serve minimal or modified functions.

Microevolution

A change in allele frequencies in a population over generations.

Four Mechanisms of Microevolution

Mutation, genetic drift, gene flow, and natural selection.

Bottleneck Effect vs. Founder Effect

Bottleneck: sharp reduction in population size. Founder: a few individuals establish a new population.

Gene Flow

Movement of alleles between populations due to migration and subsequent interbreeding.

Modes of Natural Selection

Directional (favors one extreme), Disruptive (favors both extremes), Stabilizing (favors intermediate phenotypes).

Red Queen Hypothesis

Species must continuously evolve to maintain fitness alongside coevolving interacting species.

Hardy-Weinberg Equations

p + q = 1 (allele frequencies); p² + 2pq + q² = 1 (genotype frequencies).

Hardy-Weinberg Variables (p, q, p², 2pq, q²)

p = allele A freq; q = allele a freq; p² = AA freq; 2pq = Aa freq; q² = aa freq.

Calculating Allele Frequency (p) directly from genotype counts

p = [2 × (count of AA) + (count of Aa)] ÷ [2 × (total population)].

Determining Relatedness on Evolutionary Trees

Trace lineages back to find the most recent common ancestor; recency of shared node determines relatedness, not tip position.