First, a common way to find out what protein-coding genes do is to mutate them in animals such as mice and zebrafish to see what happens. Second, funders are turning down applications to study these unknown proteins because of the risk of people spending years working on them without any results. That might be a mistake. That means these proteins have been conserved over the billion or so years since our ancestors split from those of yeast.
We corrected where a quarter of the mystery proteins are found. Most variations are harmless or have no effect at all. However, other variations can have harmful effects leading to disease. Still others can be beneficial in the long run, helping a species adapt to change. It is estimated that the human genome contains more than 10 million different SNPs. Some SNPs, however, are responsible for giving us unique traits, such as our hair and eye color.
Other SNPs may have subtle effects on our risk of developing common diseases, such as heart disease, diabetes, or stroke. Copy Number Variation CNV At least 10 percent of the human genome is made up of CNVs, which are large chunks of DNA that are deleted, copied, flipped or otherwise rearranged in combinations that can be unique for each individual. These chunks of DNA often involve protein-coding genes.
This means that CNVs are likely to change how a gene makes its protein. Since genes usually occur in two copies, one inherited from each parent, a CNV that involves a single missing gene could lower the production of a protein below the amount needed. Having too many copies of a gene can be harmful, too. Single Gene Mutation Some genetic variations are small and affect only a single gene.
Single gene mutations are responsible for many rare inherited neurological diseases. Normal genes often have triplet repeats, in which the same triplet amino acid code occurs multiple times like a stutter. These repeats are usually harmless. In the huntingtin gene, triplet repeats of 20 to 30 times are normal. The mutation creates an abnormally shaped protein that is toxic to neurons.
A few things are clear. First, for most people, a complex interplay between genes and environment influences the risk of developing these diseases. Second, where specific genetic variations such as SNPs are known to affect disease risk, the impact of any single variation is usually very small.
Finally, beyond changes in the DNA sequence, changes in gene regulation — for example, by sRNAs and epigenetic factors — can play a key role in disease.
Scientists search for connections between genes and disease risk by performing two kinds of studies. In a genome-wide association GWA study, scientists search for SNPs or other changes in the DNA sequence, comparing the genomes of subjects people, laboratory animals or cells that have a disease and subjects that do not have the disease.
In another type of study called gene expression profiling, scientists look for changes in gene expression and regulation that are associated with a disease.
Both kinds of studies often use a device called a DNA microarray, which is a small chip, sometimes called a gene chip, coated with row upon row of DNA fragments. Increasingly, scientists are conducting these studies by direct sequencing, which involves reading DNA or RNA sequences nucleotide by nucleotide. Sequencing was once a time-consuming and expensive procedure, but a new set of techniques called next-generation sequencing has emerged as an efficient, cost-effective way to get a detailed readout of the genome.
Genetic tests are often used to confirm the diagnosis of disease in people who already have symptoms, but they can also be used to establish the presence of a mutation in individuals who are at risk for the disease but who have not yet developed any symptoms. In the laboratory, GWA studies and gene expression profiling studies are leading to insights into new possibilities for disease prevention, diagnosis and treatment. When scientists identify a gene or gene regulatory pathway associated with a disease, they uncover potential new targets for therapy.
Genes tell a cell how to make proteins. Roughly speaking, each gene is a set of instructions for making one specific protein. Proteins are a diverse group of large, complex molecules that are crucial to every aspect of the body's structure and function. Collagen, which forms the structural scaffolding of skin and many other tissues, is a protein. Insulin, a hormone that regulates blood sugar, is a protein. Trypsin, an enzyme involved in digestion, is a protein.
So is the pigment melanin, which gives hair and skin its color. Still other proteins regulate the body's production of proteins. Genes sometimes affect characteristics in indirect ways. For example, genes affect the size and shape of your nose, even though there's no such thing as a "nose size" protein. But directly or indirectly, the way genes influence your traits is by telling your cells which proteins to make, how much, when, and where.
A gene has several parts. In most genes, the protein-making instructions are broken up into relatively short sections called exons.
These are interspersed with introns, longer sections of "extra" or "nonsense" DNA.
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