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77 Beneficial Mutations
Key Idea: Beneficial mutations increase the fitness of the organisms that possess them, but they are relatively rare. A beneficial mutation is one that provides a selective advantage by increasing an individual's fitness. Beneficial mutations are rare relative to harmful mutations, but if they are heritable, they can spread through the population. Some beneficial mutations are not very common in the human population. This is because the mutations have only been in existence for a relatively short time, so the mutations have not yet had time to become widespread.
it:Utente:Cits The village of Limone, Italy
` Mutation: Apolipoprotein A1-Milano (a mutation to the apolipoprotein A1 protein). ` Effect: Helps remove cholesterol from the blood by transporting it to the liver. The mutation causes a change to one amino acid and increases the protein's effectiveness at transporting cholesterol by ten times. ` Benefit: Reduces incidence of heart disease by reducing plaque build up in the arteries (atherosclerosis). ` Origin: The mutation can be traced back to Limone, Italy, in 1644. ` Mutation: Lactose tolerance/lactose persistence. ` Effect: Continued production of lactase enzyme in adults allows the milk sugar lactose (found in dairy products) to be digested. ` Benefit: Adults can digest lactose and gain the nutritional benefits from consuming dairy products. The ability to digest lactose is lost as the young mammal is weaned and lactase production declines. ` Origin: Lactose tolerance first evolved in cattle or camel-raising populations in Northern Europe, East Africa, and the Middle
East around 10,000 years ago.
Italy
Until 1932, the only way to reach the town was over steep mountains or across the lake by boat.
Limone
Brescia Lake Garda
Verona Lactose free milk allows lactose intolerant adults to consume milk without experiencing unpleasant side effects
10% 90%
The ability to digest lactose remains highest in populations with a long history of consuming natural milk products. For example, 95% of people of Northern European descent are lactose tolerant. In contrast only 5-10% of people from East Asia can digest lactose. Adults without lactose tolerance have adverse reactions to dairy products including abdominal cramps, diarrhoea, and vomiting.
1. Explain why many beneficial mutations have not spread through the entire human population?
2. (a) Why would the ability to digest lactose in adults have first developed in cattle-raising populations?
(b) What is the advantage of being able to digest lactose as an adult?
