Third Letter in .NET framework

Maker QR Code JIS X 0510 in .NET framework Third Letter

In addition to the protein-coding transcripts, an organism s DNA produces other RNA transcripts that assist with the production of proteins These other RNAs fall into several categories For purposes of this book, I won t bore you by listing them All you need to remember is that the most important category for evolution is ribosomal RNA Ribosomal RNA (abbreviated rRNA) is the class of RNA molecules that makes up the ribosomes, the cellular factories that produce proteins Ribosomal RNA is of special interest to evolutionary biologists because all organisms need ribosomes for protein production; therefore, ribosomal RNA can be used for a couple key evolutionary tasks: Understanding relationships between different organisms: Ribosomes provide a character that can be compared across all branches of life Most characteristics aren t shared across all branches of life Take eyes, for example Few things have eyes As a result, comparing a human with, say, a stalk of broccoli and a mushroom based on similarities and differences in the structure of the eye is impossible But humans, mushrooms, and stalks of broccoli do all have ribosomal RNA (In case you re curious, you and the mushroom are a fair bit more similar to each other at the ribosomal level than either of you is to the broccoli!) Determining historical relationships between species: Beyond explaining the level at which people and fungi share similarities, the really fascinating thing about ribosomal RNA is that evolutionists can use nucleotide sequences to determine the historical relationships among species In other words, it can help clarify which branch of the tree of life an organism belongs to You can read more about the tree of life in 9 Ribosomal RNA isn t important just as a tool for evolutionary biology It s also important to the proper functioning of the cell so much so that 80 percent of the RNA in a given cell can be ribosomal RNA The other categories of noncoding RNA are transfer RNA (abbreviated tRNA), which is involved in assembling the amino acids that make a protein, and a growing collection of small RNA molecules (we keep discovering new ones) that seem to be involved with the regulation of gene expression a fancy way of referring to the process of deciding which genes get turned on and off in any given cell (Think about it: All your cells have all your genes, but the genes needed to make your eyes aren t expressed in your fingers, or vice versa)

Oh, the poor gene It has fallen mightily from its halcyon days of being defined as the fundamental unit of heredity Back then, it was clear that somehow, some way, specific bits of information were passed from parent to offspring No one had any idea exactly what these bits were, but it was clear that they existed, and we called them genes Now that we understand genetic information is contained in an organism s DNA, we ve booted er, defined what we mean by gene more precisely

When most people think about heritable traits, they think about genes Unfortunately, the term gene is a little too general for a discussion of evolution Instead, you need to know a little more about how the DNA strand is put together As I state earlier in this chapter, DNA is simply long strings of nucleotides, abbreviated A, C, T, and G That s good for starters, but you need to know a bit more The word gene is commonly used in a couple of different but related ways: To refer to a specific place in an organism s genome: An organism s DNA contains a lot of information, including all the instructions for building and maintaining that particular life form The different instructions for different genes are located in different places along the DNA sequence A specific location of a gene in an organism s DNA is called a locus (plural loci, pronounced low-sigh) To refer to the exact sequence of the DNA at a specific place (or locus) in the genome: The sequence of nucleotides at a specific locus can differ among organisms These different sequences are called alleles Take the locus that stores the information to make the blood type protein When scientists examine this locus in several individuals, they find variations; some alleles code for type O blood, some for type A blood, and so on The exact sequence of the ACTG alphabet is different, and this is why people have different blood types Using the first, you might refer to a gene for blood type, but using the second, you d refer to a gene for type O blood the specific DNA sequence that results in a particular blood type Both definitions are workable as long as you keep track of which one you re using In this book, when I talk about genes, I m referring in most instances to the loci And when I m referring to alleles, I let you know