Classification and evolution: active recall

It groups organisms that can interbreed to produce fertile offspring and are reproductively isolated from other such groups. It can be difficult to apply to fossils, asexual organisms and some hybridising populations. State the evidence and limitations rather than treating one definition as universally straightforward.

Nested groups range from broad categories such as domain and kingdom to genus and species. Organisms in a narrower shared group generally share a more recent common ancestor within that classification. The hierarchy is a system for organising relationships, not a ladder of progress towards a best organism.

It combines a genus name with a specific epithet to identify a species, conventionally with the genus capitalised and the epithet lower case. It supports consistent naming across languages. The second word alone is not necessarily unique across all genera.

Comparable sequences can reveal similarities and differences that inform estimates of common ancestry. Use homologous regions and suitable analyses. Similarity is evidence to interpret with other information; one short matching sequence does not by itself establish an entire evolutionary history.

It represents an inferred common ancestor or divergence of lineages. Relatedness depends on shared ancestry, not simply on how close the tips appear on the page. Branch lengths represent time or change only if the diagram supplies that meaning.

Individuals differ, and some differences affect survival or reproductive success in a particular environment. If those differences have an inherited basis, the contributing alleles can change in frequency across generations. Mutation generates new alleles; selection does not deliberately create the mutation an organism needs.

It concerns contribution to subsequent generations in a specified environment. Greater strength or survival is relevant only insofar as it affects reproduction and inheritance. An advantageous trait in one setting can be disadvantageous in another, so fitness is contextual rather than an absolute ranking.

Directional selection favours phenotypes towards one side of a distribution and can shift its average. Stabilising selection favours intermediate phenotypes relative to extremes and can reduce variation. Explain the environmental pressures and reproductive consequences rather than merely naming the shape of a graph.

Drift changes allele frequencies through chance sampling between generations, particularly in small populations. Selection involves systematic differences in reproductive success associated with inherited traits. Both can occur together; a frequency change alone does not prove the allele was selectively advantageous.

Reduced gene flow allows populations to diverge through mutation, selection and drift. Differences can eventually prevent successful interbreeding even if contact resumes. Geographic separation can start this process but does not guarantee speciation immediately or provide the only possible route.

Resistant variants may survive and reproduce more successfully when an antimicrobial removes susceptible competitors. Resistance genes can also spread between bacteria. The treatment selects among variation; it does not normally cause every individual to acquire the exact useful mutation in response to need.

Variation within populations can influence their capacity to respond to changing conditions and can reduce problems associated with inbreeding. Species richness records a different aspect of diversity. Effective conservation also considers population size, habitat, connectivity and the particular threats, rather than relying on one count.