Learning about genetics is like learning a foreign language! Here you will find various tips and explanations of concepts that I initially found confusing.
Humans have 23 pairs of chromosomes (46 in all!) with one copy coming from Mom and one copy from Dad. These chromosomes are made up of DNA, which contains a code made of nucleotide bases (A, C, G, and T). There are about 3 billion pairs of nucleotide bases in our DNA.
A gene is a segment of a chromosome that codes for a protein, and we have about 20,000 genes in the human genome. Genes can contain anywhere from hundreds to thousands of nucleotide base pairs, and the proteins that they code for are what makes us, well, humans. The proteins can be part of the structure of our cells, signaling molecules, or enzymes that help our cells to function.
SNPs (Single Nucleotide Polymorphism):
So the A’s, C’s, G’s, and T’s that make up our DNA code are important! Three nucleotides together make up a codon that codes for a specific amino acid. We have 20 different amino acids that are strung together in different arrangements to make up proteins in our bodies.
A SNP, or single nucleotide polymorphism, is a change in one of the nucleotide bases. So where most people may have an adenine (A), some people may have cytosine (C). It is a mutation, or change, in the DNA. If the mutation is found in more than 1% of the population, it is referred to as a SNP.
So these variations in our genes are what makes us all different! A change in the genes that code for the protein that gives our hair its color can change the amount of protein (and color) of our hair.
Some SNPs change the amino acid sequence in a gene, and some SNPs have no effect on the gene. Some changes to the amino acid sequence have a big effect on the function of the gene, and some have very little effect. That is why we need to look at research studies to see what actually happens in people when they have a certain SNP.
So how do you know if what a research study shows is important? In research studies, you will often see p-values listed to show the statistical significance their finding. A p-value is just part of the statistical calculations to see if the result is different than what could be due to random chance. P-values less than 0.05 are usually considered to be statistically significant. Dummies Guide to Genetics explanation of p-Value
Odds Ratio (OR): Often in research studies, you will also see the term OR value. In the simplest terms, this should indicate the odds of (whatever the researcher studied) happening compared with a control group. If the OR =1, then the outcome of the study is the same as the control. Here is a good explanation: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2938757/ and another http://en.wikipedia.org/wiki/Odds_ratio
Here is a quick video that sums genetic testing up: