What factors other than natural selection influence...?
Interactive Study Guide
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Guiding Question 10.2
What factors other than natural selection influence the evolution of a population?
Why You Should Care
Genetic drift and its variations, the bottleneck and founder effects, are all ways that the proportion of genes in a population may randomly change. You should care about this because the genetic diseases that typify different ethnic groups came to be prominent in those communities through random accumulation of genes in the population. Many ethnic groups have accumulated genetic disorders that are rare in the general population but common enough within their populations that couples are encouraged to get genetic counseling before starting a family.
Test Your Vocabulary
Choose the correct term for each of the following definitions:
Term
Definition
When a small group with only a subset of the larger population’s genetic diversity becomes isolated and it evolves into a different population, missing some of the traits of the original.
The change in gene frequencies of a population over time due to random mating that results in the loss of some gene variants.
When population size is drastically reduced, leading to the loss of some genetic variants, and resulting in a less diverse population.
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Correct.
Incorrect.
1.
All of the following scenarios depict populations that have lost genetic variation. Determine whether the following scenarios are depicting genetic drift, the bottleneck effect, or the founder effect.
1) Northern elephant seals were hunted until there were only around 30 individuals living in 1890. Restrictions have allowed their numbers to climb back up to the thousands now. The seals have a patriarchal breeding season: One dominant male will command breeding rights for up to 10 females and prevent other males from breeding.
A.
B.
C.
2) Afrikaners are members of an ethnic group in South Africa that are mostly descendents of a single shipload of European immigrants that landed there in the mid-1600s. One of the men on that ship had the gene for Huntington’s disease, which is a terminal illness that doesn’t exhibit symptoms until sufferers are middle-aged (hence, reproductively mature). Cases of Huntington’s disease among Afrikaners are significantly higher than the frequency among humans in general.
A.
B.
C.
3) Suppose there is a small hypothetical population of a species of daisy that is isolated by mountains. The daisy has two variations in flower color: red and white. Red was never very common, and one year, only one red-flowered plant was able to reproduce, but that plant had a chromosomal defect that prevented its seeds from germinating. The following year, only white-flowered plants were found in the population.
A.
B.
C.
4) Cheetahs, a species of large felines that are the fastest land animals on Earth, live in highest densities in southern Africa, but small populations can be found in the Middle East and even India. Regardless of where a cheetah comes from, it has been found that skin grafts are never rejected between individuals. Normally, organ transplants and skin grafts fail when individuals are too genetically distinct from one another, and an allergic reaction causes rejection of the foreign tissue. There is evidence that this low genetic variability has existed since the last ice age.
A.
B.
C.
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Because the seals’ numbers were greatly reduced but they weren’t randomly accumulating changes or moving to a new territories, this is an example of the bottleneck effect.
