Question
A scientist is studying the allele frequencies in a population over several generations to help determine if the population is undergoing evolution. The data are shown in the table.
Generation Number | Frequency of Allele A1 | Frequency of Allele A2 |
1 | 0.81 | 0.19 |
2 | 0.74 | 0.26 |
3 | 0.62 | 0.38 |
4 | 0.49 | 0.51 |
(a) Describe why looking at allele frequencies over several
generations could be used to determine if a population is
undergoing evolution.
(b) Describe the changes in alleles A1 and A2 from generation 1 to
generation 4.
(c) Evaluate the scientist’s hypothesis that this population is
undergoing evolution based on the data available.
(d) Explain how the data would differ if individuals with the
genotype A1A2 were more likely to survive than individuals with
the genotype A1A1 or individuals with the genotype A2A2.
▶️Answer/Explanation
Ans:
(a) If the allele frequencies in a population are changing, the population is evolving. So looking at allele frequencies in a population over time can help determine if the population is evolving.
(b) The frequency of the A1 allele decreased from generation 1 to generation 4, and the frequency of the A2 allele increased from generation 1 to generation 4.
(c) The scientist’s hypothesis that this population in undergoing evolution is supported by the data because the allele frequencies are changing.
(d) If individuals with the A1A2 genotype were more likely to survive than individuals with the A1A1 or A2A2 genotypes, over time, it would be expected that eventually the frequencies of the A1 and A2 alleles would approach 0.50.
Question
Wildfires in the western United States have drastically reduced the size of some animal populations and destroyed the habitats of other animal populations.
(a) Describe how wildfires can create the bottleneck effect in a population.
(b) 90% of the habitat of a spotted owl colony was destroyed by a wildfire. A small percentage of the surviving owl population migrated to a new habitat. Explain the type of genetic drift this illustrates.
(c) The banana slug, Ariolimax columbianus, lives in the redwood forest in the mountains near Santa Cruz, California. A wildfire in these mountains in the summer of 2019 divided the slug’s habitat with a large area of dry ash that the slugs cannot cross. Predict the effect this had on the genetic diversity of the banana slug population.
(d) Justify your prediction from part (c).
▶️Answer/Explanation
Ans:
(a) Wildfires could create a bottleneck effect by drastically reducing the population size so that all the individuals who carry rare alleles (that were present in the original population) might not survive. Those rare alleles would then be eliminated from the population.
(b) This scenario illustrates the founder effect since a very small percentage of the spotted owl population is colonizing a new habitat and that small group might not have the same allele frequencies as that of the original population.
(c) The genetic diversity of the banana slug population in this area likely decreased.
(d) Since the population of banana slugs was randomly separated into two smaller groups that could not interbreed, each of the subgroups would have less genetic diversity.
Question
The California kangaroo rat, Dipodomys ingens, is considered an ecosystem engineer for its role in creating extensive burrowing systems that can change soil characteristics and provide habitats for other species. Fur color in D. ingens ranges from white to sandy to brown. Ecologists counted the number of D. ingens in an area before and five years after a large mudslide killed the majority of the kangaroo rats in the area. Data are shown in the table.
Fur Color | Number Before Mudslide | Number Five Years After Mudslide |
White | 75 | 0 |
Sandy | 165 | 140 |
Brown | 60 | 160 |
(a) Describe the probable cause of the change in frequency of fur
color phenotypes in D. ingens after the mudslide event.
(b) Identify an appropriate control group for this study.
(c) Analyze the data with regard to how the mudslide affected the
frequencies of fur color phenotypes in D. ingens.
(d) The burrows created by D. ingens provide habitats for many lizard
species. In order to prevent future mudslides, retaining walls were
constructed on the hillsides in the area, and the number of D.
ingens in the area decreased by over 85%. Predict the effect of
this on the lizard species diversity in the area, and justify your
prediction.
▶️Answer/Explanation
Ans:
(a) The mudslide changed the environment of the area so that darker-
colored kangaroo rats had a survival advantage after the mudslide and the lighter-colored kangaroo rats had a survival disadvantage
after the mudslide.
(b) An appropriate control group would be a similar habitat with a
similar species in which a mudslide did not occur.
(c) Five years after the mudslide, there were more brown-colored
kangaroo rats in this area and no kangaroo rats with white fur. After
the mudslide, brown-colored kangaroo rats had a survival advantage over the white-colored kangaroo rats. (The brown-
colored kangaroo rats had fur color that was similar to the color of the surrounding habitat, so it was more difficult for predators to see
the brown-colored kangaroo rats.) Therefore, the relative numbers
of brown-colored kangaroo rats increased over time.
(d) If there are far fewer D. ingens in this area, there will be fewer
burrows for the lizard species to occupy and the diversity of the
lizard species in the area will decrease.