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Chapter 2

BIO220H1 Chapter Notes - Chapter 2: Amylase, Starch, Hydrolysis

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John Stinchcombe

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Reading Article 2 – Demeter’s legacy: rapid changes to our genome imposed by
Farmers had to adapt to benefit from energy-rich food from farming
Natural selection increased copy number of gene that codes for starch-digesting enzyme
in farming population
Genetic adaptation to new diet since agricultural revolution
Agriculture: a poisoned chalice
In general farming = source of abundance
But in archaeological records find farmer’s bones anaemic
When initially transition from hunter-gathering to farming:
oLots of disease b/c farmers not adapted to new diet
oCaused deleterious digestive disorders
How did they adapt to new food supplies?
oCultural adaptation
Could process foods (cook/ferment) to increase digestibility
oGenetic changes
Change in regulation of food metabolism
Gene encoding enzyme for starch hydrolysis adapted to increases in
starchy food
Adjusting the spit to the pot
Consumption of starch exert selective pressure in genome
oNumber of copies of amylase-encoding AMY1 gene varies between individuals
oCorrelation between AMY1 genotype and phenotype (amylase concentration in
oPopulation w/ traditional starch-dense diet have higher AMY1 copy number than
population with lo-starch diet
oFind lower AMY1 copy number in chimpanzees than humans
Suggest that low AMY1 copy number = ancestral state in humans
Amylase concentration was probably initially low in saliva of hunter-
Then increased w/ high-starch diets (farmers)
Facilitate digestion of new food supply
A vita daily amount of cereals and milk
Human groups independently acquired extra copies by positive selection, not shared
oA lot of high AMY1 copy number in unrelated populations
Also see convergent evolution to favour lactase persistence in humans
Why lactase + starch tolerance beneficial to farmers?
o(1) Starch + lactose usually detrimental effects on human health unless have
enough amylase + lactase
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