Understanding Genetic Testing - why the lab and technology do matter
We are same but different when it comes to our basic genetic code written in 3.1GB of alphabet called DNA. Each humans DNA is approximately 6 feet long but it is only 2 nm in thickness. We are all humans and most of our DNA is very similar but each of us have differences in the DNA code called single nucleotide polymorphisms (SNPs). DNA code is written in 4 main letters: A, T, C, G. The letters are combined in words: “TATA”, “TAGTATATAG” along DNA. Some words mean nothing, some are responsible for regulation of other words, and some words code for proteins and other molecules like RNA which regulate life. During each of cell divisions the DNA from one cell is first replicated (doubled) and then split into two sister (or brother) cells; each with same amount of DNA as a mother (or father cell). DNA in each cell is arranged in chromosomes. Humans have 46 chromosomes: 44 of them are called autosomes as there are the same in men and women and 2 of them are called sex chromosomes X and Y. The 44 chromosomes are actually made of 22 pairs of similar chromosomes: for example we have two of chromosome no 1, two of chromosome no 2 etc. Scientists often write this as our cells having 2N where N represents half of all DNA material a single cell has. When it comes to sex chromosomes females have 2 X chromosomes, and men have one X and one Y chromosome. Presence of Y chromosome is necessary for normal sperm production and it plays role in fetus development into male or female. So each of our cells other then sperm and eggs have 44 autosomal chromosomes and 2 sex chromosomes: 46,XX (females) and 46,XY (males). Sperm and egg have half of chromosomes: 22,X or 22,Y so when they are combined together the child will have 46,XX or 46,XY. The process of splitting cells into sperm and egg is called meiosis and is a main area of my research.
To have adequate amount of DNA for cell divisions the mother cells have to double (duplicate) amount of DNA in process called replication hence during mitosis the cells have 4N amount of DNA before they split their DNA into 2N again. Although process of replication is well controlled the errors of replication can and do occur each day in our bodies. Most of such errors are corrected, the ones which are not corrected may either have no effect on the cell function, may result in cell death (apoptosis), or may lead to cancer, infertility, neurodegenerative disorders etc. Such changes in DNA code which lead to abnormal function of the cells are called mutations. Mutations are necessary for life to evolve and adapt to changes in environment, hence they are key element of human evolution but if they lead to disease we obviously want to know about them and find the ways to correct them or help our patients.
Mutations which happen in specific group of cells within our bodies are called somatic mutations. Mutations which are present in every cell in our body from time of conception are called germline mutations (indicating that we inherited them from our parents).
Genetic testing is group of advanced laboratory and mathematical methods which links changes in DNA sequence (genetic test), change in DNA letters, to the health or disease. We purposefully say “links” as genetic testing assumes probability that by detecting change in DNA sequence the particular individual will be affected by specific disease. This simply is a fact that no test in medicine or biology is 100 % accurate, as nature has ability to correct and modify a lot of genetic changes which we accumulate each day of our lives.
What tests are available for men with infertility, developmental problems, or sexual issues?