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How is DNA Related to genes?


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August 02, 2010 12:54PM

DNA is the substance which exists in the form of long strands of 'bases' (4 different types) which combine to form 'codes' to enable cells to grow and function as appropriate for each species, and the body part within each organism. 'Genes' are chunks of code, each of which forms part of a strand of DNA. Each strand of DNA is called a Chromosome, and the number of strands/chromosomes is fixed in each species, but varies from one species to another. Each organism has 2 sets of chromosomes, one from each parent. Where an organism has different genes from each parent (say brown eyes from one parent, blue eyes from the other parent), one or the other gen will be dominant, although it does get more complicated than that - you need to read some genetics books). In this example, brown is dominant to blue because the brown eye gene actively makes pigment, wheras the blue gene simply doesn't, or at least, not much. Therefore in a person with one brown gene and one blue gene, the brown gene will make enough pigment to give brown eyes, although they might be a lighter shade of brown that a person with 2 genes actively producing pigment. (Before anyone says, yeah, yeah, grossly simplified I know, just trying to get the basic concept across.)

Every cell in a body has the whole set of DNA for the species, but there are mechanisms, governed by HOX genes, which normally regulate things so that each cell only activates those genes relevent for where it is in the body. For example, all heart muscle cells carry the genes for (say) eye colour, but they only actually use the genes relevent for being a heart muscle cell.

You may have seen those breeds of fancy chickens & pigeons (at an agricultural show or petting zoo perhaps?) with feathery feet. This is an example of how selective breeding has managed to over-ride normal HOX gene controls, by bringing feather growth genes which would normally only be active on wing cells on legs as well.