The Onion Test -- Answered, Part 2
The onion test is a simple reality check for anyone who thinks they have come up with a universal function for non-coding DNA. Whatever your proposed function, ask yourself the question: Can I explain why an onion needs five more times DNA for this function than a human?
As I have mentioned in an early blog entry, the test is kind of silly -- why would non-coding DNA have just one function? But let's put that aside and consider another thought. What if humans, and onions for that matter, do not contain all the information in their DNA needed for their construction? You may think this idea is preposterous but I will explain below why it is obviously true. And since it is true, DNA size doesn't matter that much.
Think of the human body as being made of parts which are in turn made from smaller parts; and those smaller parts are in turn made by assembling even smaller parts, and on and on. The information for specifying how to make many of these parts is in the coding sections of DNA which specify which amino acids to string together to make proteins. These protein parts are in turn assembled to make more complex parts or tools for making other types of parts.
The information for making some parts (or tools for making parts) is not contained in human DNA. One example of such a part (or tool) is Vitamin K. Vitamin K1 is used to help fold some proteins used to make blood into the proper shape and is synthesized by plants. Vitamin K2 is involved in bone metabolism and is its various forms are synthesized by bacteria that live in our intestines. A short list of parts made by other organisms (and not humans) which are essential for making humans would be the essential amino acids, the essential fatty acids, and many vitamins. I suspect someone T. Ryan Gregory could list hundreds of such parts and there are likely thousands more which have yet to be discovered.
Some of the parts made by onions which are required by humans include all but one of the essential amino acids, some essential fatty acids, and vitamins A, B1, B2, B3, B5, B6, C, E and K. Onions also absorb from the environment raw materials such as calcium, copper, iodine, iron, magnesium, manganese, molybdenum, phosphorus, potassium, selenium, sodium and zinc; and we can acquire those minerals by eating them.
So what's for dinner tonight? A variety of raw or lightly cooked fruits and vegetables I hope.