founder mutation a special class of genetic mutations that often cause human disease can be used as...

Founder Mutation •A special class of genetic mutations that often cause human disease •Can be used as a tool to trace the migration and growth of specific human populations over thousands of years

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Founder Mutation

•A special class of genetic mutations that often cause human disease

•Can be used as a tool to trace the migration and growth of specific human populations over thousands of years

In everyone with a founder mutation

• The damaged DNA is embedded in larger stretch of DNA identical to that of the founder

• Phenomenon known as “identical by descent”• The entire shared region of DNA is known as

the haplotype• The age of the founder mutation can be

estimated by determining the length of the haplotype – they get shorter over time.

Page 3: Founder Mutation A special class of genetic mutations that often cause human disease Can be used as a tool to trace the migration and growth of specific

Examples of Founder Mutations

HFE iron overload far NW Europe S & E across Europe protection against anemia

CFTR cystic fibrosis SE Europe/Middle East W & N. across Eur. Protection form diarrhea

HbS Sickle cell disease Africa/Middle East To New World protection from malaria

FV Leiden Blood clots Western Europe worldwide protection from sepsis

ALDH2 alcohol toxicity Far East Asia N & W across Asia Protection from alcoholism hepatitis B

LCT Lactose intolerance Asia W & N across Eurasia consumption of milk from domesticated animals

Page 4: Founder Mutation A special class of genetic mutations that often cause human disease Can be used as a tool to trace the migration and growth of specific

PTC: GENES AND BITTER TASTE

• In 1931, a chemist named Arthur Fox was pouring some powdered PTC into a bottle. When some of the powder accidentally blew into the air, a colleague standing nearby complained that the dust tasted bitter. Fox tasted nothing at all. Curious how they could be tasting the chemical differently, they tasted it again. The results were the same. Fox had his friends and family try the chemical then describe how it tasted. Some people tasted nothing. Some found it intensely bitter, and still others thought it tasted only slightly bitter.

Page 5: Founder Mutation A special class of genetic mutations that often cause human disease Can be used as a tool to trace the migration and growth of specific

Virtually all non-tasters worldwideare descended from a founder individual who had specific alterations in this gene

The founder mutation is extremely ancient- probably more than 100,000 years old.

Page 6: Founder Mutation A special class of genetic mutations that often cause human disease Can be used as a tool to trace the migration and growth of specific

Seven different forms of the PTC gene exist in sub-Saharan Africa

But only the major taster and the major non-taster forms have been found at significant frequency outside of African populations.

Page 7: Founder Mutation A special class of genetic mutations that often cause human disease Can be used as a tool to trace the migration and growth of specific

PTC

• PTC stands for phenylthiocarbamide. Also known as phenylthiourea, the chemical structure of PTC resembles toxic alkaloids found in some poisonous plants.

Page 8: Founder Mutation A special class of genetic mutations that often cause human disease Can be used as a tool to trace the migration and growth of specific

“I’ll have the salad”• Plants are much more likely

than animals to contain toxins. Because avoiding bitter plants would severely limit their food sources, strict herbivores have fewer bitter taste genes than omnivores or carnivores. Instead, animals that graze on plants have a high tolerance to toxins. Grazers have large livers that are able to break down toxic compound

Page 9: Founder Mutation A special class of genetic mutations that often cause human disease Can be used as a tool to trace the migration and growth of specific

Curiously, there are also tasting and non-tasting chimpanzees. Unlike non-tasting humans, chimps that cannot taste PTC appear to lack functional PTC receptors

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