dna molecules
Copying and passing on genes genetics In which we consider the dynamics of genes and gene expression, and how genome dynamics leads to families of genes and facilitates evolutionary change. We consider how DNA is organized within a cell and how its organization influences gene expression. Finally we consider the behavior of regulatory networks at the molecular level and the role of molecular level noise in producing interesting behaviors. At this point we have introduced genes, DNA, and proteins, but we have left unresolved a number of important questions. These include how genomes are organized, how they evolve, how new genes and alleles are generated, and how they work together to produce the various behaviors that organisms display.327 We will touch on such trendy topics such as epigenetics which is probably less interesting than most suppose and the rather complex molecular and cellular level processes behind even the simplest biological behaviors. The details, where knownand often they are notare beyond the scope of this course, but the basic themes are relatively straightforward, although it does takes some practice to master this type of thinking. The key is to keep calm and analyze on! Genomes and their organization Genomes are characterized by two complementary metrics, the number of base pairs of DNA and the number of genes present within this DNA. The number of base pairs is easier to measure, we can count them. This can, however, lead to a mistaken conclusion, namely that the number of base pairs of DNA within the genome of a particular species, organism, or even tissue within an organism is fixed and constant. In fact genomes are dynamic, something that we will return to shortly. The genome of an organism and generally the cells of which it is composed consists of one or more DNA molecules. When we talk about genome size we are talking about the total number of base pairs present in all of these DNA molecules added together. The organism with one of the largest known genomes is the plant Paris japonica; its genome is estimated to be ~150,000 x 106 millions of base pairs.328 In contrast the haploid human genome consists of ~3,200 x 106 base pairs of DNA. The relatively small genome size of birds ~1,450 x 106 base pairs is thought to be due to the smaller genome size of their dinosaurian ancestors.329 That said there are interesting organisms that suggest that in some cases, natural selection can act to dramatically increase or decrease genome size without changing gene number. For example, the carnivorous bladderwort Utricularia gibba, has a genome of 327.