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1. (1) No mutations allowed, (2) only random mating, (3) the population needs to be large, (4) no gene flow is allowed, and (5) no natural selection.
2. Recall that you should always start by finding the frequency of the recessive (q) allele. Tan is the recessive phenotype (bb) and 40% of the snails are tan, then bb = q2 = 0.4. Take the square root of 0.4 to get q = 0.63. By applying the Hardy-Weinberg equation that summarizes the two alleles (p + q = 1), you can determine that p equals 1 – 0.63 = 0.37. The first question asks what percentage of snails are heterozygous. You know from the second equation that 2pq equals the percentage of heterozygous critters, so by plugging in your p and q values . . . 2(0.63)(0.37) = 0.47. The number of heterozygous snails would be 118 (rounded) snails. The number of homozygous dominant individuals would be 251 × (p2), or 251 (0.37)2 = 35 (rounded) homozygous dominant snails.
3. If a population suddenly suffers a drastic reduction in numbers due to a catastrophic lava flow, the remaining population will eventually repopulate. The reestablished population has very little genetic diversity due to the bottleneck effect.
4. This is an example of disruptive selection. The most-numerous medium-smelly bugs are removed, and the two extremes (slightly smelly and extremely smelly) are now the most-fit survivors and will become the most-represented phenotypes.
5. Write the Hardy-Weinberg equation that tallies the different alleles for a given gene: p + q = 1. Next, write the equation that summarizes all the given genotypes possible: p2 + 2pq + q2 = 1. The homozygous dominant genotype is represented as p2, the homozygous recessive genotype is q2, and the heterozygous genotype (both pq and qp) is 2pq.
6. 
7. Evolution in a population that occurs because of a chance change in allele frequency is referred to as genetic drift. For example, a small number of individuals may leave their original population and start their own. If these colonizing individuals happen to carry an assortment of alleles that are not similar to their original population, their new population will have a different allele frequency. This is an example of founder effect.
8. Stabilizing selection reinforces the current most-fit phenotype by removing organisms with the extreme phenotypes.
9. c. If an organism shows the recessive phenotype, its genotype must be homozygous recessive (q2). You can determine the frequency of the recessive allele (q) by taking the square root of 0.35; q = 0.59. You also know that only two allele options are available for this particular gene (dominant and recessive), and adding them both must equal 100%:
p + q = 1
therefore
p = 1 - q; p = 0.41
The frequency of heterozygous individuals in a population is determined with 2pq:
2 (0.41) (0.59) = 0.48 = 48%