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Chapter 16 Vocabulary
1. Allele frequency – the percentage of an allele within a gene pool
2. Allopatric speciation – occurs when a populations becomes geographically or physically isolated
from each other, preventing the two sub-populations from interbreeding and exchanging
genetic material.
3. Assortative mating – the selection of a mate based on a similarity of characteristics
4. Bell curve – a bell shaped graph that shows the standard distribution of a trait.
5. Biological species concept – the principle that defines a species as those organisms that can
produce offspring together.
6. Directional selection – process that directs evolution toward one extreme trait, when it is shown
that an individual with this extreme trait is more fit to survive than individuals with an average
form of the same trait. Individuals at the opposite extreme are selected out.
7. Disruptive selection – a type of natural selection that favors individuals with extreme variations
of the trait, individuals with the average form are less fit and are selected out.
8. Emigration – movement of individual(s) out of the population (permanently)
9. Gene flow – the movement of genes into or out of the population.
10. Gene pool – the sum total of all of the genes for all of the traits in a population.
11. Genetic drift – a shift in allele frequencies within a population due to random chance
12. Geographic isolation – the physical separation of a population into two or more subpopulations.
13. Gradualism – model of evolution in which there is slow gradual change over long periods of time
that leads to biological diversity.
14. Hardy-Weinberg Principle of Genetic Equilibrium – that stability of gene frequencies across
generations – (non evolving populations)
15. Immigration – the movement of individuals into a population
16. Microevolution - change in allele frequencies over time within a population.
17. Morphology – the study of the internal and external structure and form of an organism
18. Morphological species concept – characterizes a species by body shape and other structural
features.
19. Phenotypic frequency – a ratio stating the number of time a specific phenotype occurs in a
population in a single generation.
20. Population genetics – the study of evolution from a genetic point of view
21. Postzygotic isolation – a barrier to successful breeding that occurs after fertilization, such that
the offspring is not viable (doesn’t survive) or is infertile.
22. Prezygotic isolation – a barrier to successful breeding that occurs before fertilization, such as
egg/sperm incompatibility or differences in mating time or behavior.
23. Punctuated equilibrium – a theory that speciation occurs during brief periods of rapid genetic
change.
24. Reproductive isolation – the inability of formerly interbreeding organisms to produce offspring.
25. Sexual selection – the preferential choice of a mate based on specific phenotypic trait.
26. Speciation – the formation of a new species
27. Stabilizing selection – a type of natural selection in which the average form of a trait causes an
organism to have great fitness. The extremes of the trait are selected against.
28. Sympatric speciation - the process through which new species evolve from a single ancestral
species while inhabiting the same geographic region.