What is DNA?
DNA, or deoxyribonucleic acid, is the basis of a person’s genetic material. It can be thought of as the blueprint or instruction manual that tells the body how to grow and develop properly. The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Base pairs link together and are arranged in two long strands that form a spiral called a double helix. DNA base A always pairs with T and C always pairs with G. Human DNA consists of about 3 billion base pairs, collectively referred to as the human genome. The order, or sequence, of these bases determines the specific instructions in the manual, similar to the way that letters of the alphabet appear in a certain order to form words and sentences.
What are chromosomes?
DNA is organized into packages called chromosomes. Everyone has 23 pairs of chromosomes, or 46 total chromosomes, in each of their cells. Chromosomes are organized into pairs because everyone receives one copy of each pair from their mother and one from their father. The first 22 pairs of chromosomes are labeled 1 – 22 from longest to shortest. The last pair is called the sex chromosomes and determines if a person will be a girl or boy. Girls have two “X” chromosomes while boys have one “X” and one “Y” chromosome. Each chromosome has a constriction point called a centromere, which divides the chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the “p arm.” The long arm of the chromosome is labeled the “q arm.” When a special staining technique is applied to chromosomes in a laboratory, a specific pattern of dark and light bands is present. This banding pattern is used to describe the location of specific genes.
What is a gene?
A gene is a specific region of DNA, located on a specific chromosome that holds the instructions to make a molecule called a protein. Different proteins have different functions in the body, and can determine things like hair color, eye color, or how a person breaks down medication. Humans are estimated to have between 20,000 and 25,000 genes in total. Just as every person has two copies of each chromosome, every person has two copies of each gene. One copy of each gene was inherited, or passed down, from each parent.
What are alleles?
Alleles are different versions of the same gene. Different alleles can cause the body to produce slightly different versions of the same protein in different people. This is one reason why there may be differences in hair color, eye color or how fast medication is broken down between different people. There may be many different alleles for a single gene present among individuals in the general population.
What are genotypes?
Genotype is a word used to describe the combination of alleles a person has for a specific gene. A person can have two copies of the same allele or one copy of two different alleles. Genotype may also be used to describe the combination of alleles a person has for a collection of genes. As a verb, genotype may be used to refer to the process of determining a person’s gene sequence through genetic testing.
What are phenotypes?
Phenotype is a word used to describe the physical effect that a person’s genotype has on their body. A person’s genotype determines their phenotype for many different characteristics. Examples of this are a person’s hair color, eye color, or how fast they break down medication.
What are SNPs?
SNPs (pronounced “snips”) are single nucleotide polymorphisms, the most common type of genetic variation among people. Each SNP represents a change at a specific DNA base pair. For example, a SNP may replace a cytosine (C) with a guanine (G) in the DNA sequence of a gene. SNPs occur normally throughout a person’s DNA, with an average of 1 in every 300 base pairs. This is equal to approximately 10 million SNPs in the human genome. Many SNPs are located in the DNA between genes and have no effect on a person’s health. However, if a SNP occurs within a gene or a region near a gene, they may play a more direct role in disease by affecting the gene’s function. If a specific SNP allele has been associated with a change in a gene’s function, genetic testing can be done to determine which allele a person has. This information can then be used to predict a person’s phenotype, such as how fast they break down medication.
What is pharmacogenomics?
Pharmacogenomics is the study of how genes affect a person’s response to drugs. This relatively new field combines pharmacology (the study of medication) and genomics (the study of genes and their functions) to predict what medications at what doses will be most effective for individuals based on their genotypes.
Many drugs that are currently available are prescribed as “one size fits all,” but they don’t work the same way for everyone. It can be difficult to predict who will benefit from a medication, who will not respond at all, and who will experience unwanted side effects.
A variety of SNPs have been identified that are associated with how fast a person will break down certain medications or how well they will respond to a medication. The goal of pharmacogenomics is to combine a person’s genetic information with information about how specific medications are broken down in the body to make more personalized medication choices. Physicians may use this information to choose what medications to prescribe to different individuals and what doses will have the best effects.
Human Genome Resources. (n.d.). NCBI. Retrieved May 27, 2014, from http://www.ncbi.nlm.nih.gov/genome/guide/human/resources.shtml
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