Chapter 9

• Gene pool - the total alleles in a population
• Allele frequency - relative abundance of particular allele copy
• Species have typically been identified using morphology (physical structures of the organism).
• Directional Selection is when the extreme variation of a trait is selected.
• Disruptive Selection is when both extreme variations in a trait are selected.
• Stabilizing selection is when the middle variation of a trait is selected.
• Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex (intrasexual selection).
• Speciation is the formation of new species from existing species.
• Speciation occurs when members of interbreeding populations become reproductively isolated from other groups and begin to evolve independently.
• Reproductive Isolating Mechanisms are any behavioural, structural, or biochemical traits that prevent individuals of different species from reproducing successfully together.
• Reproductive Isolating Mechanisms can be used to differentiate species.
• Reproductive Isolating Mechanisms are not applicable to asexual reproduction.
• Pre-zygotic isolating mechanisms, also known as prefertilization barriers, prevent fertilization.
• Post-zygotic isolating mechanisms, also known as post fertilization barriers, prevent hybrid zygotes from reproducing.
• Species that occupy separate habitats or separate niches of the same habitat do not encounter one another to reproduce.
• Temporal Isolation: Two species in living in the same range are kept separate because they have different breeding times/seasons.
• Behavioural Isolation is a distinct mating ritual by one species that prevents members of different species from recognizing or selecting a mate.
• Allopatric Speciation is the most common form of speciation, where new species form within isolated gene pools.
• Sympatric speciation is a less common and rare form of speciation, where new species form within the same population.
• A population is split into two or more isolated groups by a geographic barrier, such as a glacier, lava flow, or change in water levels.
• Allele frequencies may change due to Genetic Drift or Natural Selections, which could result in reproductive isolation and the formation of a new species.
• A new species forms from within a population.
• Chromosomal changes create post-zygotic isolating mechanisms.
• Diploid and polyploid are examples of chromosomal changes that create post-zygotic isolating mechanisms.
• Allopatric speciation is a form of speciation where several new species are produced.
• An ancestral species invades many new geographically diverse areas.
• The populations become adapted to the different environments through natural selection.
• Darwin’s finches are an example of allopatric speciation.
• Mammals after the dinosaur extinction are an example of allopatric speciation.
• Human activities can fragment habitats and isolate populations.
• Examples of human activities that fragment habitats and isolate populations include converting wilderness to cropland, building roads, and building subdivisions.
• Flooding large areas to build hydroelectric dams is an example of a human activity that fragments habitats and isolates populations.