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In this topic of IBDP Biology, we will learn about the two main problems with selective breeding / artificial selection.
Genetic Bottlenecks
In IBDP Biology, a genetic bottleneck is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing.
- Population bottlenecks increase genetic drift - the process of change in allele frequencies.
- They also increase inbreeding due to the reduced pool of possible mates.
- Reduced genetic variation means that the population may not be able to adapt to new selection pressures, such as climatic change or a shift in available resources.
In IBDP Biology, Example: Northern elephant seals
- Hunting reduced their population size to as few as 20 individuals at the end of the 19th century.
- Their population has since rebounded to over 30,000.
- However, they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.
Example: cheetahs
- About 10,000 years ago - because of climate changes - all but one species of the cheetah became extinct.
- With the drastic reduction in their numbers, close relatives were forced to breed.
- Therefore, all cheetahs became closely related.
- Cheetahs exhibit much lower levels of variation than other mammals.
- In most species, related individuals share about 80 percent of the same genes.
- With cheetahs, this figure rises to approximately 99 percent.
- The genetic inbreeding in cheetahs has led to low survivorship (a large number of animals dying), poor sperm quality, and greater susceptibility to disease.
- Cheetahs lack the ability to adjust to sudden changes in the environment, such as disease epidemics, and have unusually high susceptibility to certain viruses.
Founder effect
- A founder effect occurs when a new colony is started by a few members of the original population.
- This small population size means that the colony may have:
- reduced genetic variation from the original population.
- a non-random sample of the genes in the original population.
- The new population may be distinctively different, genetically and phenotypically, from the parent population.
- In addition, there is a raised probability of inbreeding, resulting in an unusual number of defects due to recessive genes.
- For example, the Amish populations in the United States, which have grown from a very few founders but have not recruited newcomers.
- They tend to marry within the community
- They and exhibit founder effects phenomena:
- Eg Polydactyly extra fingers and toes are more common in Amish communities than in the US population.
- Founders are likely to be birds and rodents - since they have the best migration abilities.
- In the common case of island speciation, founders may:
- Have better swimming capabilities
- Have more fuel reserves and better thermal insulation.
- Founders may tend to be extremely physically fit - and possess more stamina and strength than most members of the population.
This is the end of this topic
