Dictionary: December 2008 Archives

What's all this DNA stuff? Here are some useful terms you may hear when you are having a DNA test performed to determine a family or biological relationship.

DNA - Deoxyribonucleic Acid - this is the biologic substance found in the nucleus of cells of all human beings.  DNA, inherited from a biological parent, is the basis of our heredity or ancestry.  DNA contains the code from which all our physical characteristics are determined as well as the instructions for making living organisms.  A single strand of DNA is composed of four different chemicals - Adenine (A), Thymine (T), Cytosine (C) and Guanine (G). 

Chromosome - these are groups of the DNA molecules found in a cell that are held together by the above four proteins.(ATCG)  Different kinds of organisms have different numbers of chromosomes but all are created at conception, arranged in pairs and consist of one set of  chromosomes inherited from the mother (mtDNA) and the other from the father (Y-DNA).  Humans have 23 sets of chromosomes - one pair will decide the sex of the child (XX)Female and (XY)Male.  These are the thread-like symbols you see in your Biology books. 

Y-Chromosome - the genetic material passed from father to son at conception.  The Y-chromosome is passed unchanged except for the rare defining mutations. 

Buccal Swab - the method by which a majority of DNA collections are performed today.  A large cotton tipped swab is swabbed against the inside of the cheek using gentle pressure in order to collect enough cells (not saliva) to amplify under the PCR method. 

Haplogroups - anthropologists study of population genetics and the mutations that occurred during migration and geographic manifestations.  The use of Short Tandem Repeat markers predicts or estimates one's Haplogroup to be within18 categories and 80 additional sub-groups and clades.  The STR marker is only an estimate. 

Mitochondrial DNA - the genetic material passed from mother to all of her offspring, save for a rare mutation that may occur in some instances. 

Mutation - a genetic inconsistency occurring naturally in all living organisms.  This is a permanent structural alteration in our DNA.  Mutations, may or may not, improve an organism's chance of survival.   In speaking of genetic mutations, the reference is no way relates to abnormal medical conditions or gene functions. 

Genetic Marker - a segment of DNA with an identifiable physical location on a chromosome and whose inheritance can be followed.  A marker can be a gene, or it can be some section of DNA with no known function.  Because DNA segments that lie near each other on a  chromosome tend to be inherited together, markers are often used as indirect ways of tracking the inheritance pattern of a gene that has not yet been identified, but whose approximate location is known. 

Allele - one of the forms of a gene at a particular location on a chromosome.  Different alleles produce various inherited characteristics, such as eye color, hair color or blood type.  Individuals have dominant and recessive forms of alleles.  Do not use the on-line eye color charts as proof of biological relationships - these are absolutely not reliable as they do not take into consideration naturally occurring mutations that have been passed on.
 

Polymerase Chain Reaction (PCR) - this is the process by which copies of our specific DNA segments are made from a DNA sample.  In a DNA Paternity test, DNA are amplified so they can be analyzed to determine whether the alleged father and tested child have common loci (position of a gene on a chromosome), supporting the existence of a biological relationship.  This process has been extensively used for paternity testing.  Large databases have been accumulated for accurate DNA analysis.  This large database enables paternity testing via PCR to have the highest power of exclusion. 

Restriction Fragment Length Polymorphism (RFLP) - this is process that relies on the genetic uniqueness of an individuals to determine a biological relationship to another individual.  No two persons (except for identical twins) have the same DNA.  A DNA sample is treated with specific enzymes to create fragments.  The size of the fragments are then measured and statistically analyzed.  If too many fragments do not have a match, the a biological relationship is considered excluded or not possible.  This technique increased the power of the exclusion of biological relationships to 99.99 % and greater. 

History of DNA Testing for Paternity
1920s Blood Type - identifying one blood type only and ability to exclude only 30% of the population - not useful or conclusive in proving paternity.
1930s Blood Groups - measured inherited proteins in the blood and ability to exclude 40% of the population - not useful or conclusive in proving paternity.
1970s HLA Typing - cannot differentiate between related alleged fathers (brothers, uncles, grandfathers) and but had the ability to exclude 80% of the population.  The test required a large amount of blood from all participants and was therefore not used on infants younger than 6 months.
1980s RFLP  - ability to exclude 99.99% of the populations
1990s PCR - ability to exclude 99.99% of the population and oral swab method preferred.  This is the method by which we perform our DNA Tests in New Jersey *732-632-8830*