Genetics

 

Half of your DNA is determined by your mother's side, and half is by your father. So, say, if you seem to look exactly like your mother, and had gotten all phenotypes from her, perhaps some DNA that codes for your body and how your organs run was copied from your father's genetic makeup.

So close, yet so far. This quote, taken from a high school student's submission in a national essay contest, represents just one of countless misconceptions many people have about the basic nature of heredity and how our bodies read the instructions stored in our genetic material (Shaw et al. 2008). Although it is true that half of our genome is inherited from our mother and half from our father, it is certainly not the case that only some of our cells receive instructions from only some of our DNA. Rather, every diploid, nucleated cell in our body contains a full complement of chromosomes, and our specific cellular phenotypes are the result of complex patterns of gene expression and regulation.
In fact, it is through this dynamic regulation of gene expression that organismal complexity is determined. For example, when the first draft of the human genome was published in 2003, scientists were surprised to find that sequence analysis revealed only around 25,000 genes, instead of the 50,000 to 100,000 genes originally hypothesized. Clues from studies examining the genomic structure of a variety of organisms suggest that much of human uniqueness lies not in our number of genes, but instead in our regulatory control over when and where certain genes are expressed.

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