Name: ______

Chapter 17 Worksheet Packet

  1. Define stabilizing selection
    Push towards an intermediate phenotype
  2. Define Directional selection
    Push towards one extreme phenotype
  3. Define Disruptive selection
    Pushes toward either extreme phenotype
  4. Starlings ( a type of bird) produce an average of 5 eggs in each clutch. If there are more than five, then the parents cannot adequately feed the young. If there are fewer than five, predators may destroy the entire clutch. This is an example of?
    Stabilizing selection
  5. The occurrence of large or small beak sizes among seed crackers in the absence of medium-sized beaks is an example of?
    Disruptive selection
  6. A scientist measures the circumference of acorns in a population of oak trees and discovers that the most common circumference is 2 cm. What would you expect the most common circumferences(s) to be after 10 generations of stabilizing selection?
    VERY VERYVERYVERY close to 2 cm
  7. Refer to question 6, but this time answer what you would expect after 10 generations of disruptive selection?
    Something far from 2 cm
  8. Refer to question 6, but this time answer what you would expect after 10 generations of directional selection that promotes small size?
    Something definitely smaller than 2cm
  9. What types of individuals in a population are represented by the two ends of a bell curve?
    The extremes of the phenotypes in continuous variation
  10. If a cow develops a preference for eating white flowers and ignoring pink and red ones, what type of selection is being demonstrated?
    Directional (away from the white phenotype)
  11. Label each type of selection below (solid is original, dashed is after)

For each of the nine examples below, give the (a) name of the isolating mechanism, and (b) tell whether it affects mating or fertilization.

  1. Fireflies have a unique lighting pattern. The frequency of lighting is species-specific. Fireflies in the same area will not mate with those having a different lighting frequency
  2. Behavioralb. Mating
  3. A group of bears was separated when the landmass they were living on split up. One group eventually became black bears and brown bears, the other, polar bears
  4. Geographical / Ecologicalb. Mating
  5. Horse and donkeys produce males, but the mules are sterile
  6. Hybrid sterilityb. Fertilization
  7. Two species of butterflies are found in Michigan, but one species is found only near rviers and streams, the other near lakes
  8. Geographical / Ecologicalb. Mating
  9. In some bee populations, only large bees are big enough to unfold flower petals and obtain nectar and pollen
  10. Mechanicalb. Mating
  11. Two parents produce a hybrid offspring that lives only a short time and dies
  12. Hybrid inviabilityb. Fertilization
  13. Two closely related species live in the same area and are capable of interbreeding but one releases pollen in February and the other in March
  14. Temporalb. Mating
  15. A cross between two fish species occurs, but development only occurs up to the 16-cell stage (at which the embryo dies)
  16. Hybrid inviabilityb. Fertilization
  17. In Drosophila, when sperm from one species enters the other species, the sperm is immobilized and unable to fertilize the egg
  18. Gamete incompatibilityb. Fertilization