Question

16. Which mode of natural selection is demonstrated by the Ginkgo tree today remaining essentially similar morphology since the Mesozoic era? a. stabilizing b. directional c. diversifying d. sexual e. artificial 17. Which scenario will demonstrate disruptive (diversifying) selection? a. There is heterozygote advantage (heterozygous individuals have the highest fitness). b. Female flies collect sperm from different males in her sperm bag. c. Individuals with intermediate phenotype are inferior competitors against homozygous individuals d. Insects become resistant to the most popular brand of insecticide. 18. Mechanisms of evolution have to be accompanied by in order for allopatric speciation to occur a. mistakes in meiosis b. temporal isolation c. geographic barrier d. behavioral isolation 19. Long-distance dispersal of a small group of individuals to isolated islands will most likely result in a. allopatric speciation c. high incidence of inbreeding e. neither a, b nor c is unlikely to occur b. evolution by genetic drift d. a, b & c 20. Which reproductive isolating mechanism confirms that horses and donkeys are different species? Note the mules are the offspring of horse & donkey parents. a. hybrid sterility b. behavioral isolation c. habitat isolation d. sperm/egg incompatibility

Answer 1

16. Correct option: (a)

Explanation: If the tree has remained essentially similar in morphology over time, it means that all variations in morphology were selected against and only the existing variation was selected for again and again. This is known as stabilizing selection.

Why not option b, c, d, e:

• In directional, the morphological trait will shift and change over time.
• In diversifying, two or more morphological phenotypes would exist which would be on extreme ends in trait value from each other.
• In sexual selection, trait value evolves based on the preference of the opposite sex, which is not happening here.
• In artificial selection, humans select for certain traits and breed organisms to perpetuate these traits, which is not happening here.

17. Correct option: (c)

Explanation: Heterozygotes occupy the intermediate population while the homozygotes have traits that are extremely far away or opposite to each other. If homozygotes are selected, it represents a disruptive selection.

Why not option a, b, d:

• a--Stabilizing selection
• b--Sexual selection
• d--artificial or directional selection

18.  Correct option: (c)

Allopatric speciation occurs when two species similar in traits and behavior are separated by a geographical barrier.

19. Correct option: (e)

Explanation: Small populations with lesser chances of dispersal will have higher chances of allopatric speciation, inbreeding, and genetic drift.

20. Correct option: (a)

Explanation: Hybrid sterility is the post-zygotic fertilization barrier that is a reproductive isolation barrier between horses and donkeys.