Evolution Practice Questions

Chapters 17

Part I. Fill in the blank.

  1. __Evolution______is defined as a change in populations over a period of time.
  1. __Fitness______in an evolutionary sense means that organisms are successful in passing on their genes to the next generation.
  1. ___Natural_____ selection, or “survival of the fittest,” means that those organisms who have traits that are better suited to their environment are more likely to survive and reproduce than those with less desirable traits.
  1. Natural selection works on an organism’s Phenotyperather than itsgenotype.
  1. A(n) gene pool consists of all the genes, including the alleles for each gene, that are present in a population.
  1. A gene pool typically contains different alleles for each heritable trait.
  1. The number of times that an allele occurs in a gene pool compared with the number of times other alleles for the same gene occur is called the allele frequency of the population.
  1. In the diagram below, use circles to represent the alleles within each segment of the population. Draw the Balleles as solid circles and the balleles as outline circles. The total number of individuals in this population is 25 ; the total number of alleles is 50 .

  1. How many alleles for black fur are in the sample population and what percentage of allele frequency does that represent?

20 (B) for black fur 20/50(total alleles) = 40% frequency for B

  1. How many alleles for brown fur are in the sample population and what percentage of allele frequency does that represent?

30 (b) for brown fur 30/50 (total alleles) = 60% frequency for b

  1. Describe how a geneticist might be able to tell that this population is evolving.

The allele frequency within the population is changing

  1. Can you determine whether an allele is dominant or recessive on the basis of the ratio of phenotypes in the population? Explain your answer.

No because the phenotypic ratio depends on the allele frequencies of the dominant and

recessive alleles, and the frequency of alleles has nothing to do with whether the allele is

dominant or recessive

  1. Read each description below and identify whether it refers to stabilizing, directional, or disruptive selection.
  1. During the Industrial Revolution in England, the peppered moth population became darker over time as the trees became darker from pollutants. DIRECTIONAL
  2. Poison dart frogs appear as either bright orange or bright blue.DISRUPTIVE
  3. Most small anole lizards are between 3 and 6 inches long.STABILIZING
  1. Why are zebras and horses considered to be members of two different species if they can interbreed and produce a zorse? In other words, why is the zorse considered to be a hybrid organism?

The zorse offspring although possible, is not able to reproduce (the zorse is sterile). Because the zorse cannot pass on its own genetic information it cannot form a new population and will not evolve.

  1. Explain the difference between genetic drift associated with the bottleneck effect and the founder effect. How does each type of drift affect variation and allele frequencies within the resulting populations, when compared to the original populations?

Both bottleneck and the founder effect are types of genetic drift (random and small populations). The bottleneck results from a sweeping change that eliminates the majority of individuals in the original population (forest fire, flood, earthquake, landslide etc). The founder effect involves a few members of a population leaving a population and traveling to a new territory where it starts a new population that may evolve into a separate species (finches that left south America and inhabited the Galapagos – became Darwin’s 13 species).

Genetic drift would decrease variation (new populations are now smaller) and the allele frequency could go up or down depending on the alleles of the founding/surviving individuals that start the new population.

  1. A new bee species, which pollinates a particular flower, arises from a larger bee population that pollinates a different type of flower. Explain why natural selection would favor the evolution of isolating mechanisms between the two species?

If bees from the two species mated, their offspring might not be able to pollinate either flower type very well. Isolation mechanisms prevent bees of both species from producing offspring that are less able to survive in their environment. These mechanisms ensure that offspring have the adaptions of their parents and help the parents’ alleles to be passed on to future generations.