Lactose2 - More on Milk Two key questions: #1 Why make...

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1 More on Milk… Two key questions: #1 Why make lactose? Persistent lactase activity #2 Why this polymorphism? Normal mammalian phenotype
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2 Geographic Distribution of LM/LA (from Bloom & Sherman 2005) Our “food aid” makes people sick… Further problem of “hidden” lactose: • In 2005, US produced 300M kg of lactose • Uses: – Browning agent in bread & cake mixes – Added to processed meat (sausage, beef) – Added to soft drinks, lagers, slimming products – Injected into some chicken meat! • Hard to avoid lactose in daily diet
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3 Lactose Processing Techniques: 1. External pre-digestion by lactic acid bacteria or yeast (yogurt, sour milk, etc.) 2. Physical removal by separating curds and whey (many kinds of cheeses)
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4 How to Explain LA/LM? Note: Most explanations assume (in error) that LM is aberrant 1. The Disease Hypothesis 2. Dietary Inhibition 3. Induction (as in bacteria) 4. The Genetic Hypothesis Amoebic dysentery? Entamoeba histolytica (shown eating bacteria)
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5 How to Explain LA/LM? 1. The Disease Hypothesis 2 Dietary Inhibition 2. Dietary Inhibition 3. Induction (as in bacteria) 4. The Genetic Hypothesis Betel Nut
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6 How to Explain LA/LM? 1. The Disease Hypothesis 2 Dietary Inhibition 2. Dietary Inhibition 3. Induction (as in bacteria) 4. The Genetic Hypothesis Induction works in works in bacteria… BUT NOT in people!
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7 How to Explain LA/LM? 1. The Disease Hypothesis 2 Dietary Inhibition 2. Dietary Inhibition 3. Induction (as in bacteria) 4. The Genetic Hypothesis Good match to genetic model! From: Coevolution text The inference: LA is controlled by a single dominant allele! Today a lot is known about genetics of lactase persistence 1. Lactase itself is encoded by a gene called “LCT” on human chromosome 2.
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This note was uploaded on 11/08/2009 for the course HUMBIO 2A taught by Professor Boggs,c;durham,w during the Spring '08 term at Stanford.

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Lactose2 - More on Milk Two key questions: #1 Why make...

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