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| 7879473256 | Adaptive radiation | Period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill vacant ecological roles in their communities Example: Hawaiian plants have spread into different habitats and formed new species with strikingly different adaptations. | 0 | |
| 7879473257 | Allopatric Speciation | The formation of new species in populations that are geographically isolated from one another Example: The water in a lake may subside, resulting in two or more smaller lakes that are now home to separated populations. | 1 | |
| 7879473258 | Behavioral Isolation | Courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species. Example: Blue-footed boobies mate only after a courtship unique to their species. | 2 | |
| 7879473259 | Gene Flow | The transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes. Example: The migration of people throughout the world has increased the transfer of alleles between populations that once were isolated from one another. | 3 | |
| 7879473260 | Geographic Isolation/Barrier | The separation of two populations of the same species by a physical barrier, such as a mountain or body of water Example: Antelope squirrels are on opposite rims of the Grand Canyon and are separated from each other | 4 | |
| 7879473261 | Hybrid Breakdown | Some first-generation hybrids are viable and fertile, but hen they mate with one another or with either parent species, offspring of the next generation are feeble or sterile Example: The hybrids of strains of cultivated rice carry too many recessive alleles, making them small and sterile. | 5 | |
| 7879473262 | Hybrid fertility | Even if hybrids are vigorous, they may be sterile. If chromosomes of the two parent species differ in number or structure, meiosis in the hybrids may fail to produce normal gametes. Since the infertile hybrids cannot produce offspring when they mate with either parent species, genes cannot flow freely between the species. Example: The hybrid offspring of a donkey and a horse is a mule, which is robust but sterile. | 6 | |
| 7879473263 | Hybrid Viability | The genes of different parent species may interact in ways that impair the hybrid's development or survival in its environment. Example: Some salamander subspecies of the genus Ensatina live in the same regions and habitats, where they may occasionally hybridize. But most of the hybrids do not complete development, and those that do are frail. | 7 | |
| 7879473264 | Mechanical Isolation | Mating is attempted, but morphological differences prevent its successful completion. Example: The shells of two species of snails spiral in different directions. As a result, the snails' genital openings are not aligned, and mating cannot be completed. | 8 | |
| 7879473265 | Natural Selection | A process in which organisms with certain inherited characteristics are more likely to survive and reproduce than are organisms with other characteristics Example: Giraffes have adapted long necks because the trait of having a long neck is necessary for survival to obtain food from trees. | 9 | |
| 7879473266 | Polyploidy | A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division. Example: Polyploid bananas contain no seeds, as do other polyploidy seedless plants. | 10 | |
| 7879473267 | Post Zygotic Barrier(s) / Isolation | If a sperm cell from one species overcomes prezygotic barriers and fertilizes ovum from another species, a variety of barriers may contribute to isolation after the hybrid zygote is formed. Example: Developmental errors may reduce survival among hybrid embryos. The hybrid offspring of a donkey and a horse is a mule, which is robust but sterile. | 11 | |
| 7879473268 | Prezygotic Barrier(s) / Isolation | Block fertilization from occurring by impeding members of different species from attempting to mate, by preventing an attempted mating from being successfully completed, or by hindering fertilization if mating is completed successfully. Example: Blue-footed boobies mate only after a courtship unique to their species. | 12 | |
| 7879473269 | Reproductive Barrier / Isolation | The existence of biological factors that impede members of two species from producing viable, fertile offspring. Example: The shells of two species of snails spiral in different directions. As a result, the snails' genital openings are not aligned, and mating cannot be completed. | 13 | |
| 7879473270 | Species | A population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups. Example: Humans | 14 | |
| 7879473271 | Sympatric Speciation | The formation of new species in populations that live in the same geographic area Example: The ancestors of apple maggot flies laid their eggs only on hawthorns; however, today, these flies lay eggs on hawthorns (which are native to America) and domestic apples (which were introduced to America by immigrants and bred). Females generally choose to lay their eggs on the type of fruit they grew up in, and males tend to look for mates on the type of fruit they grew up in. So hawthorn flies generally end up mating with other hawthorn flies and apple flies generally end up mating with other apple flies. | 15 | |
| 7879473272 | Temporal Isolation | Species that breed during different times of the day, different seasons, or different years cannot mix their gametes. Example: In North America, the geographic ranges of the eastern spotted skunk and the western spotted skunk overlap, but the eastern spotted skunk mates in late winter and the western spotted skunk mates in late summer. | 16 |
