1. EVOLUTIONARY CHANGE WITHOUT SELECTION - created by Ms Mak

2. Overview Not all evolutionary changes are the result of natural selection. Some changes such as genetic drift, bottlenecks and the founder effect are not influenced by the traits of individuals. Each of these changes tends to reduce genetic diversity within a population

3. Genetic Drift Genetic Drift: is the random shifting of the genetic makeup of the next generation. is changes to allele frequency within populations and species as a result of chance; such changes are much more pronounced in small populations. allows for evolution to occur by helping to increase and change genes that are present in the gene pool.

4. Genetic Drift and Population Size The larger the size of a population, the smaller the effect of genetic drift. Genetic drift is much more pronounced in small populations than in larger ones. E.g., if you toss a coin 5 times there is a possibility that all 5 times heads may appear. However, if you toss the coin 50 times, it is more likely that heads will appear 50% of the time and tails will appear 50% of the time.

5. BOTTLENECKS Genetic bottlenecks: dramatic, often temporary, reductions in population size. result in a loss in genetic diversity. have adverse consequences for populations. eventually, the population may recover and grow to their original size again. However, the allele frequencies that were previously present may have been altered.

6. An example of this type of genetic drift is cheetahs; they have very little genetic variation because their population was subject to a genetic bottleneck. Figure 1 Severe bottleneck may decrease the chance of evolving because of a decrease in genetic variation. Figure 2

7. FOUNDER EFFECT occurs when a small number of individuals establish a new population. the allele frequencies of the new smaller population will be different from those of the original larger population. E.g., About 30 Amish people in Pennsylvania left a large population and one of the Amish had a recessive trait for shorter limbs and six fingers. The frequency of the short limbs and 6 fingers increased because of the founder effect.

8. SUMMARY Genetic drift produces evolutionary changes independently of natural selection. Bottlenecks and the founder effect enhance the influence of genetic drift. Genetic drift, bottlenecks and the founder effect increase genetic variation in species and populations.