HL 1 Biology

5.4c Examples of Evolution

<<Evolution in Action- Galápagos finches>>

  • Darwin observed 14 different species of finches
    • noticed they vary in sizes, shapes of beaks (as well as diet)
    • Darwin’s hypothesis: “one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”
  • Darwin’s finches – relationship between beak shape + diet
    • variation in shape & size of beaks mostly due to genes (environment too)
    • heritability: proportion of the variation due to genes
    • objection: significant changes caused by natural selection not been observed
    • yet G. fortis showed significant changes have occurred that are clearly linked to natural selection

<<Antibiotic resistance in bacteria – Evolution in action>>

  • Have been increasing problems of antibiotic resistance in pathogenic bacteria
  • Trends:
    • bacteria showing resistance appeared within few years after antibiotics were introduced/used on patients
    • resistance to antibiotic spreads to more species of pathogenic bacteria
    • in each species the proportion of infections that are caused by a resistant sprain increases
    • multiple resistance: strains of bacteria appear that are resistant to more and more different antibiotics
  • cumulative changes in the antibiotic resistance properties of populations of bacteria, during time antibiotics have been used to treat bacterial diseases
  • antibiotic resistance due to genes in the bacteria
  • Rapid evolution due to:
    • widespread use of antibiotics
    • rapid reproduction of bacteria (less than an hour in average)
    • population of bacteria are huge, increase chance of genes forming mutation
    • bacteria can pass genes to other bacteria by: using plasmids (allow one species of bacteria to gain antibiotic resistance genes from another species)
  • Tuberculosis: a main example
    • prison: good place for the bacteria to spread
    • many white areas in the lung: blood..
    • need to give more than one medication in order to kill all the bacteria
    • if patient doesn’t take all the antibiotics, the antibiotic resistant bacteria can multiply and patient remains sick
    • that’s why in Japan we are given medication for several days, to continue getting rid of the bacteria + avoid the evolving antibiotic resistant bacteria
  • Globalization is also the spread of diseases

<<Experimental Investigation of Evolution>>

  • “Darwin’s theory of evolution by natural selection tells us that species only change gradually as one generation succeeds another”
  • evolution experiments take a long time because significant changes occur after many generations
  • To help speed up evolution experiments:
    • computer simulations can be used
    • speed up natural process of evolution (by increasing amount of variation within a population)


Evolution in Rice Plants (p.203)

1) The investigation was done using hybrids rather than a single pure-bred variety because natural selection cannot be examined in pure bred variety because there is no variation in this pure bred population.

2) Changes present between the F3 and the F6 generations of rice plants grown at Miyazaki include the following: the  mean days of the flowering has become later in the year and the decrease in variation of the plants. We can see that in F3 the mean flowering was apparent through 72~90 days, and yet in F6 the mean flowering days is on the 110~125 days.

3) (a) It is visible that the lower the latitudes in the F6 generation, the later flowering times.

(b) The flowering is earlier when the latitudes are higher, thus causing the growing season to be shorter.

4 (a) If the investigation had been carried on until the F10 generation, the variation would have decreased due to natural selection.

(b) The collected seeds from F10 from Sapporo and Miyazaki may go through the process of natural selection again, in order to adapt to the surrounding new environment. Yet, because the seeds have already undergone natural selection for 1o generations, the seeds would be more adapted to their original environment (high latitude in Sapporo, low latitude in Miyazaki) that crop failure may occur as they are limited with the intermediate alleles to survive in the new environment (Hiratsuka).

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