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13.9 – 13.10. 3 causes of evolutionary change: 1. Natural selection 2. Genetic Drift 3. Gene Flow.

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Presentation on theme: "13.9 – 13.10. 3 causes of evolutionary change: 1. Natural selection 2. Genetic Drift 3. Gene Flow."— Presentation transcript:

1 13.9 – 13.10

2 3 causes of evolutionary change: 1. Natural selection 2. Genetic Drift 3. Gene Flow

3 Genetic Drift  Change in the gene pool of a population due to chance

4 Bottleneck EffectExample  Genetic drift resulting from a drastic reduction in population size  Northern elephant seal population reduced to about 20 individuals in the population due to human predation. Population allowed to recover. The DNA of 24 genes studied – found no variation / only one allele for each gene.

5 Founder Effect Example  Random change in the gene pool that occurs in a small colony of a population  1814 – 15 people founded a British Colony on Tristan da Cunha. One person carried a recessive allele for retinitis pigmentosa (progressive form of blindness). In the 1960’s the island descendants were samples – of 240 individuals, 4 had the disease. The frequency for the disease is much higher among islanders than the area from which the founders came.

6 Gene FlowExample  Gain or loss of alleles from a population by the movement of individuals or gametes into or out of the population  Human movement today promotes gene flow; no

7  Which type of event explains the high incidence of polydactylism found in the Amish population? Founder Effect

8  Flower population: ww = white flower; WW and Ww = purple flower; a mud slide wipes out most of the white flowered plants. What type of event occurred? Bottleneck

9  Genetic modifications from transgenic plants passed to neighboring populations of wild relatives. What type of event occurred? Gene Flow

10  Millions of greater prairie chickens once lived on the prairies of Illinois. As these prairies were converted to farmland and other uses during the 19 th and 20 th century, the number of greater prairie chickens plummeted to less than 50 individuals. The few survivors have low levels of genetic variation. What type of event occurred? Bottleneck

11  This event resulted in the world wide spread of several insecitcide-resistance alleles in the mosquito Cluex pipiens, a vector for West Nile virus and Malaria. What type of event occurred? Gene Flow

12  Reduction in geographic variation in the appearance of humans is caused by what type of event? Gene Flow

13  A few weeks after two major hurricanes swept through the Caribbean islands, fishermen on the island of Anguilla observed a large raft float to the shore. Green iguanas were seen on the raft. These iguanas are thought to have come from the islands of Guadeloupe. The allele frequencies for the founding population on Anguilla differed from those on Guadeloupe. What type of event occurred? Founder Effect

14  Humans on the island of Pingelap Atoll in the South Pacific suffered the effect of typhoon followed by a famine around Only about 20 people out a population of several thousand managed to survive. One of the survivors carried a color blindness allele. In today’s population on this island, over 1 in 20 people is afflicted with color blindness – well over 20%. In the original population about 2.5% of the people had this form of color blindness. What type of event occurred? Bottleneck


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