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Zorluk: ZorEvolution and Adaptation

A marine biologist observes an isolated population of marine iguanas over multiple decades. During repeated El Niño events, high ocean temperatures cause a dramatic decline in the preferred green algae found in deeper waters, forcing the reptiles to graze on tough, low-growing red algae clinging to shallow rocks. Biologists note that iguanas with naturally shorter snouts graze more efficiently in these conditions, resulting in higher survival and reproductive rates. After several generations, the average snout length across the entire population is significantly shorter. Which of the following best explains why this evolutionary change occurred in the population?

  1. A
    Shorter snout length is a dominant genetic trait, which causes it to automatically become the most widespread characteristic in any population over time.
  2. Natural selection favored individuals with pre-existing advantageous variations, leading to higher reproductive success and a gradual shift in the population's allele frequencies.Cevap
  3. C
    Individual iguanas gradually reshaped and shortened their snouts through continuous scraping against rock surfaces during their lifetimes and passed those modified structures to their offspring.
  4. D
    The physiological stress of severe starvation triggered adult iguanas to deliberately mutate their genetic code to develop shorter snouts before reproducing.

Cevap

Natural selection favored individuals with pre-existing advantageous variations, leading to higher reproductive success and a gradual shift in the population's allele frequencies.
Natural selection operates on heritable genetic variation already present in a population. When environmental conditions change, individuals possessing traits that improve foraging efficiency are more likely to survive, reproduce, and pass those favorable genes to their offspring, progressively shifting the population's phenotypic average over generations.

Adım Adım Çözüm

1
Identify the environmental pressure and phenotypic variation in the scenario.
The environmental pressure is food scarcity caused by ocean warming, and the existing variation is differences in snout length among iguanas.
Natural selection requires pre-existing heritable variation within a population upon which environmental selective pressures act.
2
Evaluate differential survival and reproductive success.
Iguanas with shorter snouts graze more effectively on shallow algae, surviving at higher rates and producing more offspring.
Fitter individuals contribute a greater proportion of genes to the next generation's gene pool.
3
Differentiate between population-level evolution and individual Lamarckian or directed change.
The population's overall genetic makeup changes across generations as favorable alleles increase in frequency, rather than individuals acquiring physical changes during their lifespan.
Biological evolution is defined as a change in allele frequencies within a population over time, not individual physiological adaptation.

Anahtar Kavram

Mechanism of Natural Selection and Adaptation in Populations
Tahmini Süre:1m 30s
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Evolution and Adaptation

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