How does DNA give an organism its characteristics?

Is DNA the only thing passed from generation to generation?



My understanding is that DNA is the genetic material which contains everything needed to form an organism.



But a while ago in biology, I learnt that all DNA does is code for proteins. So one combination of bases means that a cell produces a particular protein.



But what does this have to do with the organism as a whole? How does producing different proteins mean that a cow has 4 legs and a human 2?



Am I missing something?How does DNA give an organism its characteristics?
Whoa, it seems your teachers gave a lot for granted. I'll try to keep this simple - forgive me if I state the obvious but I want to make sure we're on the same page.



What passes from one generation to the other can be described as one of the maternal cells, with a nucleus rearranged so that it contains both maternal and paternal DNA. The mitochondria and chloroplasts are special cellular organelles containing their own DNA: in animals, only the maternal mitochondrial DNA is passed on.



DNA codes for proteins; more exactly, DNA codes for mRNA which codes for proteins. A piece of DNA coding for a protein is called a gene. When the protein is produced, we say that the gene is expressed.



Now a brain cell and a white cell have the same DNA, but they are very different because during and after their development, they express different genes. How is the process regulated? Let's start with a model organism:



http://en.wikipedia.org/wiki/Drosophila_鈥?/a>



In the fruit fly, four initial genes are responsible for determining where the head and the tail of the future fly will be. This is possible because the mRNAs for the 'head end' gene are present in one end of the egg and those for the 'tail end' gene in the other end. So a first rough draft of the body plan is laid. What's important is that the proteins coded by these mRNAs are capable of interacting with the DNA, promoting the expression of other genes in a cascade of activations. For example, protein E might be produced in the region of the embryo where the relative concentrations of A and B are 75 to 25, and protein E might be the placeholder for the thorax of the future insect; you can bet that all the genes coding for 'head' structures such as brain, eyes and antennae will be switched off by the presence of E, whereas the expression of genes for 'thorax' structures such as legs and wings will be encouraged. All the process is finely timed, like a circus number, and proceeds from basic shapes to finer structures; eyes and hairs do not form until the boundaries of the head and legs have been determined.



You're wrong in stating that a cow has 4 legs and a human 2: both have 4 limbs, it's only their shape that is different - a minor thing compared to their number.



One striking characteristic of animals is metamery - we're made of repetitive segments. You see this well in a fish bone, or in our spine. There are genes determining how many repetitive segments will the animal have, and genes determining what structures will be present in a given segment. These genes, called homeotic, are responsible for the most striking alterations in body plan during development. Even a single mutation in one of these genes can give rise to a fly with legs sprouting out of its head, or with an extra pair of wings. A characteristic of these genes is that they're very similar to each other and aligned on the chromosome - which makes their duplication very likely. Each subsequent duplication is nature's occasion for more bizarre experimentation. But I'm raving at this point, and you already get the picture...



Hope this helped.How does DNA give an organism its characteristics?
DNA is made up of chromosomes and proteins. These chromosomes contain specific codes from your parents genes that come together and determine your characteristics. The genes in DNA that you receive are determined by if there are recessive or dominant. So for example, if your mother has blue eyes and your father has brown eyes, you will have a 50% chance of blue eyes. This is because blue eyes are recessive, their code is b b, and brown eyes contain a dominate allele, their code is B b.How does DNA give an organism its characteristics?
Those proteins either are the structure or direct the formation of the structure.