What is DNA?
DNA is like our own personal blueprint filled with all the instructions needed to make a functioning body. DNA is contained in the "brain" of the cell, called the nucleus, and is made up nucleotides, which are chemical compounds consisting of a base, sugar, and phosphate. Bases are similar to letters of the English alphabet. Only instead of 26 letters, there are only four: adenine(A), guanine(G), cytosine(C), and thymine(T). These four "letters" when combined in different sequences make up our genetic code.
What is a Gene?
Each gene carries a complete set of instructions for a unique (or multiple) protein(s) that will perform a specific function(s) in our body. Genes can interact with other genes to produce new proteins and proteins can interact with other proteins to facilitate different functions in our body.
What is a Genome?
All together, our entire genetic make-up (called our genome), contains about 25,000 genes, which are present in the 100 trillion cells of the body. All these genes work together to make us.
What are Chromosomes?
Genes are packaged together on bigger structures called chromosomes. There are 46 chromosomes in total, which are grouped into 23 pairs. The first 22 pairs are numbered largest to smallest (1 - 22) and are called autosomes. The last pair determines gender, and is either XX (female) or XY (male).
In each pair of chromosomes, we inherit one from our mother and the other from our father. As such, we have two copies of most genes, one from each chromosome (or parent).
Each chromosome has two arms, labeled p (the shorter of the two) and q (the longer), which are connected by the centromere (a pinched in site of constriction). The centromere is very important in the division process that chromosomes undergo during cell replication and division. The ends of the chromosomes are called telomeres, which help protect the genes within the chromosomes.
In humans, the arms can be connected in either metacentric (both arms are equal in size), submetacentric (both arms are unequal in size), or acrocentric (when the p arm is very short) manners. Of note, there are five acrocentric chromosomes in the human genome: 13, 14, 15, 21 and 22.
What is a Mutation?
We all have differences in our DNA - just look around. Mutations are changes in our DNA that are considered abnormal. The majority of mutations don't cause problems and some are even beneficial.
For example, the word "color" in British English is spelled "colour." This is a benign change as the meaning of word did not change. However, other mutations may cause problems by altering the instructions of the gene, like changing the spelling from "color" to "colon." Now the words mean completely different things. In the DNA world, these changes may cause the gene to not produce a protein, produce little or too much protein, or change the protein altogether.
All of us also have normal differences (or variations) in our DNA, which are called polymorphisms. We now know that some of these polymorphisms may make us more susceptible to developing common diseases such as diabetes and heart disease. In some cases, polymorphisms may cause our body's to metabolize certain drugs differently such as ibuprofen, herceptin, codein, tamoxifen and warfarin. Click here for more information about polymorphisms.
What is a somatic mutation?
While some DNA changes are inherited from our parents, others may occur sporadically in our body in a single cell or tissue. These types of DNA changes are called focal (or somatic) mutations.
Most cells in our body divide to make new cells. The DNA in those cells needs to be replicated for each new cell. Sporadic DNA changes can occur during cell division or DNA replication as well as with environment damage, like smoking or sun exposure. Luckily, our body has mechanisms that repair DNA damage. As our body ages, however, it becomes less able to repair DNA damage and the damage may become irreparable and cause tumors.
What is an inherited mutation?
Changes in our DNA, which are inherited from our parents, are called constitutional (or inherited) mutations. These changes are typically present in every cell of our body. In autosomal dominant conditions, a single damaged gene is sufficient to cause the disorder. In autosomal recessive conditions, both genes (one from each parent) need to be damaged to cause the disease. Other additional modes of genetic inheritance include sex-linked inheritance and mitochondrial inheritance. Click here for more information about different Modes of Inheritance.