Although Selection Acts on Existing Traits, New Traits Can Evolve Selection itse

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Although Selection Acts on Existing Traits, New Traits Can Evolve Selection itself generates no new genetic variation, adaptive or otherwise. Dif- ferences in survival or reproduction occur only among variants that already exist The starvation of small-beaked individuals, for example, does not instantaneously create more variation in beak size among finches. In particular, it does not cre- ate finches with big beaks optimal for cracking Tribulus fruits. Starvation merely winnows the breeding population down to the largest-beaked birds already alive. Average . oil content of corn kernels (%) 20 This might seem to imply that under natural selection, new traits cannot evolve. But the evolution of new traits is, in fact, possible. There are two reasons: The first applies to all species, the second to species that reproduce sexually. Dur- ing reproduction in all species, random mutations produce new alleles. During reproduction in sexual species, meiosis and fertilization recombine existing alleles into new genotypes. Mutation and recombination yield new suites of traits that selection may subsequently sort among 10 Original population range O 0 20 40 60 80 10 Generation Consider, for example, an artificial selection study run at the University of Il- inois (Moose et al. 2004). Since the study began in 1896, with 163 ears of corn Figure 3.19 Persistent researchers have been sowing for next year's crop only seeds from the plants witlh the highest oil content in their kernels. In the starting population, oil content traits Data from the linois ranged from 4% to 6% by weight. After 100 generations of selection, the average Long-Term Selection Experiment oil content in the population was about 20% (Figure 3.19). That is, a typical plant document the increase in oil con- in the present population has over three times the oil content of the most oin corn kernels during 100 rich plant in the founding population. Mutation, recombination, and selectiorn together produced a new phenotype. long-term selection can re- sult in dramatic changes in generations of artificial selection The average for the 100th gener ation lies far outside the range of the founding generation. Modi- fied from Moose et al. (2004) Persistent natural selection can lead to the evolution of new functions for existing behaviors, structures, or genes. Carnivorous plants provide examples. The

Explanation / Answer

option A) is correct i.e only statements i and ii convey accurate information.

Because from the graph it can be seen that at starting generation, oil content was 5%, after 100 generations it has become more than 15% (three-fold increase).

The experiment was started in 1896, i.e nineteenth century.

The image does not depict natural selection, rather it shows artificial selection.

Oil content did not increase continuously over 100 generations, oil content sometimes increased and sometimes decreased.

Nothing can be determined about population size after 100th generation, the experiment started with 163 ears of corn.

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