How can we apply this to real life? Use the Hardy-Weinberg formula to calculate the percentage of a human population that carries the allele for a particular inherited disease: Ex: PKU. PKU occurs in about 1/10,000 babies born in U.S. If untreated, causes severe mental retardation; need a strict diet. It is a recessive genetic disease. Newborn babies are now routinely tested for PKU. A PKU baby is q2 = 1/10,000 = q = square root of.0001 or.01. p = 1 - q, or = 0.99 Carriers are 2pq or 2 x 0.99 x 0.01, or Thus,1.98% (around 2%) of the U.S. population carries the PKU allele. This is essential information for any public health program dealing with genetic diseases. (Note: Also do Punnett Square method on left.) Now-You try some problems in your UP. Remember: If they ask for frequency of an allele, that is p or q. If they ask for the % of individuals, that is pp or qq or 2pq. (The “individuals” are in the box.) Do the Punnett Square here: pq p q

We just discussed a “non-evolving” population. How can we tell if a population is evolving? Ex: What if an insect is attracted to the white flowers instead of the red, and the white get pollinated more? This could cause the population to change over the generations. This is called microevolution, evolution on a small scale. 4 examples of microevolution: 1. Genetic Drift:

1. Genetic Drift - chance causes the frequencies of the alleles to change over the generations in a small gene pool, not natural selection. (The smaller the sample, the greater the chance of deviation from an idealized result.) See example above.

2 examples of Genetic Drift: A. Bottleneck Effect - disasters (earthquakes, floods, droughts, fires) may drastically reduce the size of a population. Small surviving population may not be representative of the original population’s gene pool. Some alleles may be lost from the gene pool - reducing the overall genetic variability in a population. Ex: Cheetahs have been overhunted. Only 3 small populations are left in wild; have low genetic variability. May be less adaptable to diseases, or environmental changes.

B. The Founder Effect- a few individuals colonize an isolated island, lake, or other new habitat The smaller the colony, the less its genetic makeup represents the gene pool of the original population from which they emigrated. Ex: In 1814, 15 people founded a British colony on small islands in Atlantic Ocean. One colonist carried a recessive allele for retinitis pigmentosa; causes blindness. In 1960’s, 4/120 descendants had it and 9 were carriers - much higher frequency than in Great Britain. Tristan da Cunha. 1900’s