No, alleles/genes are the blueprints for how the car is made, not the actual car parts, to use your analogy. And, much like cars or tractors, minor variations are built around the current design, while larger design changes incorporate much larger redesigns.
Originally Posted by DBM aka FDS
However, at a certain point, the analogy breaks down because motor-vehicles are not organisms.
Alleles change because there are mutations within the genetic code. Jesus, you've been arguing this for, what, like 4 years now? You should know better.
How do they explain that? Find anything? Nope… anything stating “Look, here we can see how the allele has changed the whole gene sequence (chromosome) into something else… now we have (Presto Chango’d) stems that will eventually turn into feathers (after a couple mutations through natural selection
) after the allele for hair color (Presto Chango’s) continues to change from brown to blonde… or mutates (Presto Chango’s into something completely different)
So, short version because I don't want to waste my time too much.
DNA has four bases: ATCG. A combination composed of three bases makes up a codon, which codes for a specific amino acid, which ribosomes use to construct proteins, which are chains of amino acids.
You change the codon, you change the amino acid (sometimes; the last position in a codon usually doesn't affect which amino acid is used to make a protein), which can change the function of a protein (in varying amounts; sometimes changing a terminal amino acid on a protein will result in no change, some amino acids are very similar to one another and don't produce changes in proteins, while others can cause enormous changes with a single amino acid substitution), which can produce macroscopic changes in development or biochemistry. Depends on which protein is affected and how.
This also makes some genes highly conserved, because if they change, the organism simply dies, while other genes code for proteins that don't do a whole lot and thus can be changed quite frequently and rapidly because they don't kill the organism. The former is something like a growth hormone gene, which can kill an organism during development if it is mutated. An example of the latter is the proteins that code for certain taste-bud receptors that have an intense reaction to certain chemicals.
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