AP Biology Vocabulary & Roots: Ch. 23
1. allele- Any of the alternative versions of a gene that produce distinguishable phenotypic effects.
2. average heterozygosity-The percent, on average, of a population’s loci that are heterozygous in
members of the population.
3. balancing selection-Natural selection that maintains two or more phenotypic forms in a
population.
4. bottleneck effect-Genetic drift that occurs when the size of a population is reduced, as by a
natural disaster or human actions. Typically, the surviving population is no longer genetically
representative of the original population.
5. cline-A graded change in a character along a geographic axis.
6. directional selection-Natural selection in which individuals at one end of the phenotypic range
survive or reproduce more successfully than do other individuals.
7. disruptive selection-Natural selection in which individuals on both extremes of a phenotypic
range survive or reproduce more successfully than do individuals with intermediate phenotypes.
8. founder effect-Genetic drift that occurs when a few individuals become isolated from a larger
population and form a new population whose gene pool composition is not reflective of that of the
original population.
9. frequency-dependent selection-A decline in the reproductive success of individuals that have a
phenotype that has become too common in a population.
10. gene flow-The transfer of alleles from one population to another, resulting from the movement
of fertile individuals or their gametes.
11. gene pool-The aggregate of all of the alleles for all of the loci in all individuals in a population.
The term is also used in a more restricted sense as the aggregate of alleles for just one or a few loci
in a population.
12. genetic drift-A process in which chance events cause unpredictable fluctuations in allele
frequencies from one generation to the next. Effects of genetic drift are most pronounced in small
populations.
13. geographic variation-Differences between the gene pools of geographically separate
populations or population subgroups.
14. Hardy-Weinberg equilibrium-The condition describing a nonevolving population (one that is
in genetic equilibrium).
15. Hardy-Weinberg principle-The principle that frequencies of alleles and genotypes in a
population remain constant from generation to generation, provided that only Mendelian
segregation and recombination of alleles are at work.
16. heterozygote advantage-Greater reproductive success of heterozygous individuals compared
with homozygotes; tends to preserve variation in a gene pool.
17. intersexual selection-Selection whereby individuals of one sex (usually females) are choosy in
selecting their mates from individuals of the other sex; also called mate choice.
18. intrasexual selection-A direct competition among individuals of one sex (usually the males in
vertebrates) for mates of the opposite sex.
19. microevolution-Evolutionary change below the species level; change in the allele frequencies
in a population over generations.
20. mutation- A change in the nucleotide sequence of an organism’s DNA, ultimately creating
genetic diversity. Mutations also can occur in the DNA or RNA of a virus.
21. natural selection-A process in which organisms with certain inherited characteristics are more
likely to survive and reproduce than are organisms with other characteristics.
22. neutral variation-Genetic variation that does not appear to provide a selective advantage or
disadvantage.
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23. point mutation-A change in a gene at a single nucleotide pair.
24. population-A localized group of individuals of the same species that can interbreed, producing
fertile offspring.
25. Punnett square-A diagram used in the study of inheritance to show the predicted results of
random fertilization in genetic crosses.
26. quantitative character-A heritable feature that varies continuously over a range rather than in
an either-or fashion.
27. recessive allele-An allele whose phenotypic effect is not observed in a heterozygote.
28. relative fitness-The contribution an individual makes to the gene pool of the next generation,
relative to the contributions of other individuals in the population.
29. sexual dimorphism-Marked differences between the secondary sex characteristics of males and
females.
30. sickle-cell disease-A human genetic disease caused by a recessive allele that results in the
substitution of a single amino acid in a globin polypeptide that is part of the hemoglobin protein;
characterized by deformed red blood cells (due to protein aggregation) that can
31. stabilizing selection-Natural selection in which intermediate phenotypes survive or reproduce
more successfully than do extreme phenotypes.
Word Roots
inter- = between (intersexual selection: individuals of one sex are choosy in selecting their mates
from individuals of the other sex, also called mate choice)
intra- = within (intrasexual selection: a direct competition among individuals of one sex for mates
of the opposite sex)
micro- = small (microevolution: a change in the gene pool of a population over a succession of
generations)
muta- = change (mutation: a change in the DNA of genes that ultimately creates genetic diversity)
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