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Transcript
Factors Causing Evolution
Prairie dogs live in dense colonies consisting of a few dozen members. For much of the year
they prevent other prairie dogs from joining their colony. In late summer, however, mature
male pups are permitted to enter new colonies, thereby affecting both gene pools.
The remaining populations of the Blanchard's cricket frog, once found on Pelee Island in Lake
Erie, are endangered. A severe weather event leading to the random deaths of half the
population could lead to significant changes in allele frequencies.
A few seeds of a plant are carried by a bird or by winds to a distant volcanic island, where they
germinate and rapidly establish a large population, whose gene pool is different from the
population of plants where they originated.
A population of ground finches in the Galapagos Islands has a different genetic composition
than that of the original population from where the first few individuals came.
The northern elephant seal population was reduced by over-hunting to 20 individuals in the
1890's. Although the population had rebounded to over 30000 individuals by 1974, genetic
testing of 24 loci exhibited total homozygosity.
Members of the Amish community in Pennsylvania are all descendants of about 30 people who
emigrated from Switzerland in 1720. One of the 30 had a rare recessive allele that causes
unusually short limbs. The frequency this allele in the current Amish population is about 7%,
compared to a frequency of 0.1% in most populations.
gene flow (migration)
genetic drift (bottleneck effect)
genetic drift (founder effect)
genetic drift (founder effect)
genetic drift (bottleneck effect)
genetic drift (founder effect)