Polydactyly Polydactyly (extra fingers/toes) is a symptom of Ellis-van Creveld syndrome. The syndrome is commonly found among Amish populations in Pennsylvania. Why?

Polydactyly Genetically inherited diseases like Ellis-van Creveld are more concentrated among the Amish, because they marry within their own community. This prevents new genetic variation from entering the population. Children are therefore more likely to inherit 2 copies of the particular recessive genes that lead to genetic disease.

Polydactyly in Amish Populations This means that there is a HIGH frequency of recessive alleles for Ellis-van Creveld syndrome in the Amish population compared to the rest of the world.

Genetic Drift

The change in a population’s allele frequencies due to chance Remember – a change in allele frequencies is evolution!

Genetic Drift There are 2 ways genetic drift can occur: – The Founder Effect – The Bottleneck Effect

The Bottleneck Effect Disasters can greatly reduce the size of a population. Those that survive may not be representative of the original gene pool. – Earthquakes, floods, drought, fires, etc.

The Bottleneck Effect Does the new gene pool represent the original gene pool? Has evolution occurred?

The Founder Effect Takes place when a few individuals from a larger population colonize an isolated habitat – All of the genes from the original gene pool may not be represented in the new population.

A. Bottleneck Effect B. Founder Effect Cheetahs were once widespread in Africa & Asia. Their numbers fell drastically during the last ice age about 10,000 years ago. Those few that survived reproduced & made up the population that exists today. Bottleneck Effect

A. Bottleneck Effect B. Founder Effect The Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. Founder Effect

Genetic Drift Most common in small populations Genetic drift has negative effects on populations: – Causes a loss of genetic diversity – Less likely to have individuals that can adapt – Harmful alleles can become more common due to chance.

The potato, Solanum tuberosum, originated in South America. It was carried to Europe in the 1500s, & by the 1800s it was a staple food in Ireland. Because the potatoes in Ireland originated from the small number that were introduced, there was little genetic diversity. In 1845, a disease called potato blight swept through Ireland. None of the potatoes were resistant to the disease, so nearly every potato was killed. Since the Irish heavily depended on the potato as a food source, this led to a mass starvation & decimated 25% of the Irish population. A. Founder EffectB. Bottleneck Effect

A population of mice is 50% black fur & 50% brown fur. Owls can catch the mice with brown fur more easily, because they stand out more. After several generations, only 25% of the mice have brown fur. Is this genetic drift? A.Yes B.Nope NO! Genetic drift is RANDOM! The change in the mouse population was NOT random. Owls ate the brown mice, because they were easier to catch. Evolution occurred, but this was not genetic drift; it was natural selection!

Genetic Drift Activity On your tables, there is a beaker of 3 different types of beans. The phenotypes are in a ratio of 15:20:15. For 3 trials, RANDOMLY choose about beans. Recalculate the ratios for the new bean population.

Genetic Drift Original Population Trial #1Trial #2Trial #3 Phenotype # BeansRatio(% ) # BeansRatio(% ) # BeansRatio(% ) # BeansRatio(% ) Pinto 15 30% 7 35% 4 14 Kidney 20 40% 4 20% 10 7 Black Eye Peas 1530% 945% 4 0 Bead Totals =