Diversity of organisms links variation, species concepts, classification tools, chromosome evidence, and genome comparisons to explain biological similarity and difference.
Coverage 2010–2025 · Updated 15 Jul 2026
• Variation occurs between individuals within every species
• Continuous variation often results from polygenes and environmental effects
• Darwin's observations of variation supported natural selection
• Species can be grouped by shared morphology and structural traits
• Morphological species concept is useful in fieldwork, fossils, and many plants
• Sexual dimorphism and within-species variation can make morphology difficult
• Binomial nomenclature gives each species a universal two-part Latin name
• Genus is capitalized; species is lowercase; both are italicized or underlined
• Species in the same genus share similar traits
• Biological species concept defines species by interbreeding and fertile offspring
• It emphasizes gene flow between members of the same species
• Limits include extinct organisms, asexual species, and cases with gene flow between distinct forms
• Speciation is gradual as isolated populations diverge
• Populations may still be theoretically able to interbreed but cannot meet
• Species boundaries can therefore be partly arbitrary
• Chromosome number is usually constant within a species but varies between species
• Diploid chromosome numbers are even because chromosomes occur in homologous pairs
• Examples include fruit fly 8, rice 24, human 46, chimpanzee 48, and dog 78
• Karyotypes show chromosome number and structure in a cell
• Karyograms arrange chromosomes by length, banding pattern, and centromere position
• Human chromosome 2 supports fusion from two ancestral ape chromosomes
• A genome is all genetic information in an organism
• Members of a species share most of their genome but differ at variants
• SNPs are common single-base differences used as biological markers
• Eukaryote genomes vary in size and base sequence
• Between-species variation is much larger than within-species variation
• Not all DNA codes for proteins
• Genome size is the DNA amount in one chromosome set
• Larger genome size does not necessarily mean greater organism complexity
• Polyploidy can greatly increase genome size, especially in plants
• Whole genome sequencing began at scale with the Human Genome Project
• Current uses include evolutionary relationships, gene discovery, and pathogen research
• Future uses include personalized medicine, diagnosis, disease prevention, and vaccine targets
