When a cell makes a protein the instructions are copied from part of the DNA strand and transcribed to new molecule, called RNA. RNA molecules carry the instruction from the nucleus to ribosomes.
I believe it's A. Premature Birth (though they all seem pretty believable)
I'm not sure if I will answer the question you asked, as I many have interpreted it incorrectly. In natural selection, there must be variance in the gene pool, the total frequency of alleles in a population. Now, one of the organisms may have a gene that somehow helps them survive from the selective force much better compared to the others. If this does happen, over time the gene pool will narrow down to become just the genes of that organism that survived better in the first place because the rest would be taken care of by the selective force. So, the alleles and trait come from the first organisms that had the advantage over the others of its species.
frequency of the dominant allele in the population ... 2pq = frequency of heterozygous individuals. A population of rabbits may be brown (the dominant phenotype) or white (the recessive phenotype). Brown rabbits have the genotype BB or Bb. White rabbits have the genotype bb.