Size isn t everything: Sizing up the genome in VS .NET

Creator QR Code 2d barcode in VS .NET Size isn t everything: Sizing up the genome

Different organisms have radically different genome sizes, but not necessarily in the way you might expect You have a much bigger genome than a bacterium or a mushroom does, and at first, that seems to make a lot of sense After all, humans certainly appear to be more complex than bacteria or mushrooms We have a lot more parts arms, eyes, complicated nervous systems, and so on so it seems reasonable that our genome would be bigger Right Well maybe, and maybe not The range of genome sizes varies among several major groups of organisms Your genome is much bigger than the genome of yeast or Escherichia coli (E coli) bacteria, for example, yet many plants have more DNA that people do And just in case your ego hasn t taken enough of a hit, you should be aware that some plants don t just have more DNA than we do, but more genes as well Poplars, for example, have twice as many genes as people do For details about genome size and coding and non-coding DNA, head to 15

The unit of genome size is the number of base pairs (abbreviated bp) Why base pairs It s simple math, really and understanding how the DNA sequence works Think about the size of the human genome, which contains

about 12 billion nucleotides Because of the paired structure of DNA (A always pairs with T, C always pairs with G, and so on), when you know the 6 billion on one strand, you automatically know the 6 billion on the other strand From an information standpoint, only 6 billion independent bits of information exist As a result, scientists refer to the size of the human genome as 6 billion bp

Some DNA doesn t seem to contain much information; it s what scientists call junk DNA Some junk DNA consists of long sections in which short sequences of nucleotides repeat over and over and over Both plants and mammals have lots of junk DNA, but plants seem to have more (which explains why the fern hanging in your kitchen has more DNA than you do) That s quite a feat, considering that we humans have a lot of junk ourselves And just how much junk do we have As a matter of fact, it appears that more than 95 percent of human DNA doesn t contain any information about how to make a person! Researchers are still trying to figure out why so much of human DNA is junk a problem that I discuss in 15

Scientists have determined the DNA sequence of the entire human genome (a fact you may already know from the various news stories that accompanied the completion of the Human Genome Project) So it may come as a surprise that scientists still don t know exactly how many genes humans have Are they lazy or just unmotivated As it turns out, neither It s sometimes tricky to tell exactly when a sequence at some particular locus in human genome contains instructions used for making a person and when it contains junk And because the human genome is more than 95 percent junk, small variations in how scientists go about deciding what is a gene and what isn t can make a big difference in the total number of genes they think humans have As researchers keep refining their techniques for identifying genes in this big sea of DNA, they end up revising their numbers progressively downward Currently, they think they have a good handle on the situation and are reasonably certain that the human genome contains about 25,000 genes Is that a lot A lot is a relative thing Common intestinal bacteria have about 5,000 genes; yeast has about 6,000; the common laboratory roundworm has around 18,000; and the fruit fly Drosophila has 14,000 And many plants seem to have as many genes as human do, and some have far more