Selection and evolution：練習題

• a.0.21
• b.0.30
• c.0.70
• d.0.42

• a.

  A significant reduction in genetic diversity due to random sampling of alleles (genetic drift via the bottleneck effect).

• b.

  Directional selection completely eliminating all recessive alleles within a single generation.

• c.

  A rapid increase in mutation rates driven directly by the stress of the environmental disaster.

• d.

  An increase in the rate of gene flow between geographically isolated sub-populations.

• a.

  The standard deviation of the phenotypic distribution decreases while the mean remains constant.

• b.

  The mean value of the phenotype shifts in one particular direction over generations.

• c.

  All phenotypes have an equal probability of survival regardless of environmental pressures.

• d.

  Extremes of the phenotypic range are favoured, while intermediate phenotypes are selected against.

• a.

  Bacteria absorb antibiotic molecules and incorporate them into their cell walls to acquire immunity.

• b.

  Antibiotics kill non-resistant bacteria, leaving naturally resistant mutants to survive, reproduce, and pass on resistance alleles.

• c.

  Antibiotics induce specific targeted mutations in bacterial DNA to help them survive hostile conditions.

• d.

  Antibiotics decrease the overall mutation rate of bacteria, stabilizing advantageous metabolic traits.

• a.

  The population must experience a regular population bottleneck to eliminate deleterious recessive mutations.

• b.

  There must be high rates of gene flow between distinct populations and active directional selection.

• c.

  Mating must be strictly non-random with a preference for heterozygous genotypes.

• d.

  The population must be large with random mating, and there must be no net mutation, migration, or selection.

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