When the ranges of two different species meet, a stable "hybrid zone" occupied by hybrid individuals may form. How is this possible? Two diverged populations are capable of mating and producing viable and fertile offspring. Hybrid individuals may have reduced fitness and thus be strongly selected against. Hybrid individuals are always allopolyploid and are thus unable to mate with either of the original species. One species has a selective advantage, so as hybridization continues, the other species will go extinct. Request Answer Submit

Interspecific hybrids, if they survive, are (a) always sterile (b) always fertile (c) usually sterile (d) usually fertile (e) never sterile

Why might captive-breeding programs that reintroduce species into natural environments fail?

David Hills of Baylor University noted that three closely related species of leopard frog (genus Rana) exhibit substantialbut not completepostzygotic reproductive isolation when crossed in the laboratory. Field surveys of numerous populations in Texas and surrounding states revealed that populations of the three species breed at various times during the year. Data on the breeding schedule of both allopatric and sympatric populations of these species are presented in the Figure below. Interpret the data in the figure and explain how they may demonstrate that these frogs experience prezygotic reproductive isolation in nature. What type of prezygotic reproductive isolation do the data suggest? Source: D.M. Hillis. 1981. Premating isolating mechanisms among three species of the Rana pipiens complex in Texas and southern Oklahoma. Copeia 1981:312-319.

Figure 18.23 Which of the following statements is false? Punctuated equilibrium is most likely to occur in a small population that experiences a rapid change in its environment. Punctuated equilibrium is most likely to occur in a large population that lives in a stable climate. Gradual speciation is most likely to occur in species that live in a stable climate. Gradual speciation and punctuated equilibrium both result in the evolution of new species.

If the genotype frequencies in a population are 0.60 AA, 0.20 Aa, and 0.20 aa, and if the requirements of the HardyWeinberg principle apply, the genotype frequencies in the offspring generation will be: a. 0.60 AA, 0.20 Aa, 0.20 aa. b. 0.36 AA, 0.60 Aa, 0.04 aa. c. 0.49 AA, 0.42 Aa, 0.09 aa. d. 0.70 AA, 0.00 Aa, 0.30 aa. e. 0.64 AA, 0.32 Aa, 0.04 aa.

Prezygotic is isolating mechanisms: a. reduce the fitness of hybrid offspring. b. generally prevent individuals of different species from producing zygotes. c. are found only in animals. d. are found only in plants. e. are observed only in organisms that reproduce aseually.

Figure 19.2 In plants, violet flower color (V) is dominant over white (v). If p = .8 and q = 0.2 in a population of 500 plants, how many individuals would you expect to be homozygous dominant (VV), heterozygous (Vv), and homozygous recessive (vv)? How many plants would you expect to have violet flowers, and how many would have white flowers?

The first step leading to allopatric speciation is (a) hybrid inviability (b) hybrid breakdown (c) adaptive radiation (d) geographic isolation (e) paedomorphosis

How Can We Measure Allele Frequencies in Populations? In a population where the females have the allelic frequencies A = 0.35 and a = 0.65 and the frequencies for males are A = 0.1 and a = 0.9, how many generations will it take to reach HardyWeinberg equilibrium for both the allelic and the genotypic frequencies? Assume random mating and show the allelic and genotypic frequencies for each generation.