The Complete Idiot's Guide to a Smart Vocabulary
From Darwin to DNA: Evolution, Genetics, and Biotechnology
In This Chapter
When people talk about progress and how quickly the world is changing, they usually have some aspect of the computer or Internet revolution in mind. That's not surprising because these aspects of technology get lots of ink, and there's no shortage of high tech boosters out there who are eager and unashamed to compare the latest techno-gizmo to the invention of sliced bread. Besides the hyperbole (hye·PUR·buh·lee, noun; "speech that uses exaggeration for emphasis"), most of us use computers in our everyday lives, so it's natural to focus on them.
But there's another revolution happening as you read this, a revolution that may in the end be more profound and far-reaching than anything a mere computer can do. I'm talking about the revolution in genetics and in its close cousin, biotechnology. From cures for diseases that kill thousands of people a year to foods that have been genetically altered to increase vitamins or production (and hopefully nothing else!), these two sciences have the potential to fundamentally change our lives. To help you understand what these fields are all about, this chapter takes you through some of the most common terms. I begin, however, with not a revolution, but an evolution.
Evolution (ev·uh·loo·shun or ee·vuh·loo·shun, noun) is the theory that species change genetically over time as a result of natural selection. Small-scale changesfor example, those that effect only the appearance of a speciesare called microevolution, and large-scale changesthose that involve the origin and extinction of speciesare called macroevolution.
The driving force of evolution is natural selection (noun), the process by which organisms with inborn characteristics that make them best suited to compete and survive in their environment are therefore the ones most likely to reproduce and thus pass along those characteristics to their offspring. A characteristic that helps an organism survive is called an adaptation (ad·ap·TAY·shun, noun). The passing of characteristics from one generation to the next is called heredity (huh·RED·i·tee, noun).
An adaptation arises because of a mutation (myoo·TAY·shun, noun), a sudden and random change in the structure of an offspring's gene or chromosome that results in a new characteristic or trait not found in the parents.
Darwinism (DAR·wi·niz·um, noun) is the theory of evolution by natural selection as developed by Charles Darwin. The theory states that species develop over time because of beneficial mutations that increase the survivability of organisms, which then reproduce and pass along those mutations. Eventually (over many, many generations), these adapted organisms dominate while the unadapted organisms die off. The result is an evolved species that fully incorporates the adaptation.
Darwinism is also called survival of the fittest (where "fittest" in this case means "most adapted to the environment").
Darwin didn't have a clue how mutations arose and how they were passed along to successive generations. In other words, he didn't know about genetics (juh·net·iks, noun), the study of heredity, especially how traits are transmitted from parents to offspring and how those inherited traits vary between similar or related organism. Darwinism combined with genetics is sometimes called neo-darwinism.
DNA (dee·en·AY, noun) short for deoxyribonucleic (dee·ok·see·rye·boh·noo·KLAY·ik) acid, is a molecule that carries an organism's genetic information. (A molecule [MOL·uh·KYOOL, noun] is a group of atoms held together by chemical bonds.) Each molecule consists of two long sequences of chemical compounds called nucleotides (NOO·klee·oh·tydz, noun; see also base). In each sequence, the nucleotides are linked together in a chain, and the two chains are intertwined to form a double helix (HEE·liks).
You find DNA in a chromosome (KRO·muh·some, noun), a rod-like structure housed in the nucleus ("central part") of most cells. In human cells, there are 46 chromosomes arranged in 23 pairs. One of those pairs consists of the sex chromosomeslabeled X and Yso-called because they determine the sex of the person. Males have both an X- and a Y-chromosome, while females have two X-chromosomes.
It's the specific sequence of the dna nucleotides that determines an individual organism's inherited characteristics. More specifically, an organism's inherited traits are determined by its genes. Each gene (jeen, noun) is a segment (or sometimes several segments) of dna that determines ("codes for," in the lingo) a specific physical characteristic of an organism. Humans have roughly 30,000 to 40,000 genes.
Most organisms have special cells called germ cells (noun) that are used in the reproductive process. (This is why germ cells are also often called reproductive cells.) In a process called meiosis (mye·OH·sis, noun), reproduction begins when the germ cells split in two, with the resulting gamete (GAM·eet, noun) containing 23 chromosomes. In the female, the gamete is called an ovum (or egg); in the male, it's called a sperm cell.
When a sperm cell fertilizes an ovum, the combination has the usual 46 chromosomes. However, during this recombining of chromosomes, the genes can cross over from one chromosome to another, which shuffles the offspring's genetic makeup. It's during this crossing-over period (as well as during the initial stages of meiosis) that genes can mutate (MYOO·tate, verb), which means one or more nucleotides are moved, added, or deleted. Remember that it's these mutations that are at the heart of evolutionary theory.
A gene's purpose in life is to build a protein (PRO·teen, noun), which is a macromolecule (a large, complex molecule) that consists of a sequence of amino (uh·MEEN·oh) acids (organic compounds that consist of specific combinations of nitrogen, hydrogen, carbon, and oxygen). There are thousands of different proteins, and almost everything in the body is made of one or more proteins, including the hair, nails, muscles, organs, and hormones.
Each amino acid is created from a codon (COH·don, noun), a specific sequence of three nucleotides. (Some amino acids can be made from more than one codon.) The genetic code (noun) consists of the set of codons that make the body's full complement of 20 amino acids.
So when the body needs to make a protein, it first finds the chromosome containing the corresponding gene. It then unwinds the DNA double helix and uses one strand to create a copy of the gene's nucleotide sequence, a process called transcription (noun). After editing out some bits of the sequence that aren't required, the cell then enlists the help of a structure called a ribosome (RYE·buh·some, noun) to read the gene copy one codon at a time, producing an amino acid with each pass. This process is called translation (noun), and when it's complete, the new protein is ready for use within the body. This entire process is called protein synthesis (noun).
The genome (JEE·nome, noun) is the complete set of DNA within an organism. Note that this is not the same as saying the complete set of an organism's genes, which is called the genotype (JEEN·uh·type, noun). The difference is that there are portions of the DNA that aren't part of any genes. Some bits of DNA serve to mark the beginning and end points of genes, while other sequences don't seem to do much of anything. (The latter is called junk DNA or non-coding DNA.)
The Human Genome Project is a massive, international undertaking with the goal of understanding the entire human genome. This involves essentially two things: pinpointing where each gene is located on each chromosomethis is called mapping (noun) the genomeand determining the type and order of all the nucleotides that comprise the genome's DNAthis is called sequencing (noun) the genome. The ultimate goal is to be able to associate all hereditary human physical traits and all hereditary human diseases with specific genes. This may enable doctors to cure a disease by "repairing" one or more genes. (See also gene therapy.)
Here are some quick definitions of some other genetics terms you should know:
Industry Meets Biology: Terms from Biotechnology
Biotechnology (bye·oh·tek·NOL·uh·jee, noun) is the use of biological processes, organisms, or substances to perform specific industrial or manufacturing tasks. The "manufacture" of recombinant DNA is an example of a biotechnological process.
One of the most common applications of biotechnology is to change the structure of one or more of an organism's genes to achieve a particular result. Such an organism is described as genetically modified (adj.) or GM. Here are some GM-related words that have been in the news over the past year or two:
Questions and Exercises to Help Everything Sink In
Here's a list of the main words you learned in this chapter:
In the following questions, hover your mouse pointer over the word Answer to see the answer in your browser's status bar:
Match the word on the left with the short definition on the right:
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