![]() When the size of each group is plotted against its usage, the distribution can be approximated to a power-law function that is, the number of words (N) with a given occurrence (F) decays according to the equation N = aF - b. On grouping words that occur in similar numbers, it was noted that a small selection of words such as 'the' and 'of', are used many times, while most other words are used infrequently. Also known as Zipf's law, one of the most famous examples is the usage of words in text documents. ![]() ![]() Power-law behaviors have been observed in many different population distributions. We present this behavior in a unified framework and propose that all these observations are connected to an underlying DNA duplication process as genomes evolved to their current state. Power-law behavior provides a concise mathematical description of an important biological feature: the sheer dominance of a few members over the overall population. We show comprehensively that this behavior applies across many different genomes, for many different types of parts (DNA words, InterPro families, protein superfamilies and folds, pseudogene families and pseudomotifs), and for the many disparate attributes associated with these parts (their functions, interactions and expression levels). Here, we find many further cases of power-law behavior, for example in the occurrence of pseudogenes and in levels of gene expression. Earlier studies found power laws in a few specific cases, such as the occurrence of protein families. This observation is true in a wide variety of genomic contexts. Resultsĭespite these differences, we find that the genomic occurrence of generalized parts follows a well-known mathematical framework called the power law, with a few parts occurring many times and most occurring only a few times. Through the analysis of such inventories, it has been shown that different genomes have very different usage of parts for example, the common folds in the worm are very different from those in Escherichia coli. §Note: Sometimes alleles result from epigenetic changes (heritable changes that don't alter the sequence) - these can be referred to as epialleles and appear to be less common than alleles based on sequence polymorphisms.The sequencing of genomes provides us with an inventory of the 'molecular parts' in nature, such as protein families and folds, and their functions in living organisms. A good example of this is the ABO blood groups - traditionally we have identified three alleles Iᴬ, Iᴮ, and i, but it turns out that are multiple sequences that correspond to each of those alleles! Furthermore, two alleles that appear to the same at a phenotypic level may have different sequences. sequence differences) that separate them. However, any two alleles are likely to have multiple polymorphisms (i.e. ![]() ![]() genetic polymorphisms) being present in a population. Having multiple alleles is (usually§) a consequence of multiple different sequence variants for a gene (i.e. Polymorphism (literally "many forms") means different things in different contexts, but in a genetic context it really just means that there are differences in the sequences.įor example SNPs (pronounced "snips" - stands for single nucleotide polymorphisms) are a very common type of sequence polymorphism. Not exactly - what is true is that genetic polymorphisms are responsible for the existence of (most) alleles. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |