Why codon in the sickle cell DNA is altered ?

A missense mutation changes a codon so that different protien is created, a non-synonymous change

Explanation:

Sickle-cell disease is caused by a single point mutation in the beta hemoglobin gene that converts a GAG codon into GUG

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explanation:

plate tectonics and volcanic euptions

over time, plate tectonic processes cause continents to move to different positions on the globe.

for example, britain was near to the equator 300 million years ago, and therefore was hotter than it is today. for further details look at our climate through time poster or online map.

the movement of the plates also causes volcanoes and mountains to form and these too can contribute to a change in climate.

mountain ranges formed by plate tectonics. large mountain chains can influence the circulation of air around the globe, and consequently influence the climate.   warm air might be deflected somewhere cooler by the mountains.