seanfhear writes:
Would it be appropriate to assume a trait for an allele as an example and to speculate what could be a possible change in the function or structure of an organism if information was lost? Can you think of a simple example?
One good example is vitamin C synthesis in humans. A single point mutation, in this case a deletion, caused a frame shift in the GULO gene responsible for the synthesis of vitamin C. A frame shift is what happens when a single nucleotide is inserted or deleted.
A frame shift works like this. Say you have this simple nucleotide sequence that I've divided into triplets:
Now let's perform a single nucleotide deletion, let's say the 2nd nucleotide gets deleted. We're now left with this:
The loss of a single nucleotide has caused the framing of codons to shift, hence the name frame shift mutation. TAG has become TAC, CAT has become ATG, and GCC has become an incomplete codon CC. As you can see, a single nucleotide deletion has the potential to completely change the codon sequences and thereby the protein it is responsible for.
This is in essence what happened somewhere in the distant evolutionary ancestry of apes. A frame shift mutation in the GULO gene responsible for the synthesis of vitamin C experienced the deletion of a single nucleotide that resulted in a premature stop codon. In humans vitamin C synthesis never completes because of the premature stop codon. We have to get all our vitamin C from what we eat.
Here's a comparison of the same subsequence of the rat and human GULO gene. To make it easier to interpret I've included the human sequence twice, once with a dash where the cytosine nucleotide was, and then again with the frame shift:
[face=Lucida Console]Rat: GTA / GAG / GTG / CGC / TTC / ACC / CGA / GGC / GAT / GAC / ATT / CTG / CTG / AGC / CCC
Human: GTG / GGG / GTA / CGC / TTC / ACC / TGG / AG- / GAT / GAC / ATC / CTA / CTG / AGC / CCC (without frame shift)
Human: GTG / GGG / GTA / CGC / TTC / ACC / TGG / AGG / ATG / ACA / TCC / TAC / TGA / GCC / CC (with frame shift)
Single cytosine nucleotide deletion------------^[/face]
Sorry it's so wide.
--Percy
Edited by Percy, : Reduce width by using less of the nucleotide sequence.
Edited by Percy, : Typo.