How are the instructions for the characteristics of an organism carried ?

Alright, this might get complicated. DNA has the original characteristics, but it cannot travel outside of the nucleus, so the DNA is unzipped, mRNA attaches a complementary strand of mRNA to the template strand of DNA and then that moves out of the nucleus to the ribosomes. There, the mRNA forms Amino Acids, which form alleles, which is called the 'genotype'. Alleles come in pairs. For example, Aa might code for a part of eye color. The capital A is called dominate and the lowercase is reccessive. In a 'heterozygous' pair, there is one dominate and one reccessive. In a 'homozygous' pair there is only one type, AA or aa. If a dominate allele is there, it will be expresses. There is a lot more, but that literally took me a month to learn so I will not go into incomplete dominance, codominance, or multiple alleles here.