Biology 2483A Lecture Notes - Lecture 5: Bighorn Sheep, Allele Frequency, Natural Selection

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Natural selection acts as a sorting process. Individuals with favored traits have more offspring, and their alleles will increase in frequency in the population: population will evolve, but individuals do not, natural selection can result in differences between populations. Bighorn sheep populations have been reduced by 90% by hunting, habitat loss, and introduction of domestic cattle. Hu(cid:374)ti(cid:374)g is (cid:374)o(cid:449) restri(cid:272)ted i(cid:374) north a(cid:373)eri(cid:272)a; per(cid:373)its to take a large (cid:862)trophy ra(cid:373)(cid:863) (cid:272)ost o(cid:448)er. Case study: fish: fish that mature earlier can reproduce before they are caught; but small fish produce fewer eggs, not a steady decline, fluctuations. African elephants poached for ivory; tusks is decreasing: unintended effects of human harvesting of these animals illustrate how populations can change, evolve, over time. Increased amount of elephants that do not have tusks; because all the tusks are poached for ivory; non-tusks remain in population. Evolution: change in allele frequencies (proportions) in populations over time.

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