DNA Basics

What is DNA?
Deoxyribonucleic acid (DNA) is a molecule found in nearly all human cells and contains the information for the development and function of all living organisms. A human DNA molecule is a double helix shaped like a twisted ladder. The human genome is the complete set of human genetic information found within 23 pairs of chromosomes for each person. Half of the chromosomes come from the father and half from the mother. These 23 chromosomes reside within the nucleus of the cells and some DNA is also found in the mitochondria.

Nitrogenous Bases (ATCG)
DNA chromosomes look like long twisty ladders. The longest chromosome (1) has over 249 million rungs and the smallest (21) has over 48 million. In total there are over 3 billion of these rungs in human DNA. Each rung in the ladder will contain a pair of nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). A and T are always paired together and C and G are paired together. Although two SNPs will always be together at each spot, only one of the two values at each spot will do any coding, the other is just a backbone that holds the structure together. The side that does the coding is called the + strand and the side that is the backbone is the - strand. Sometimes in an A T pair, the A will be the coding gene and the T will be the backbone, other times it will be the reverse and the same is true for C and G pairs. For simplicity, DNA companies will therefore just record the value of a person's + strand at each spot they test.

Single-nucleotide polymorphisms (SNPs)
All human beings are 99.9% identical in their genetic makeup meaning that at out of the 3 billion genes we all have 99.9% are the same in all humans. The places where it is possible for a variance to occur are called, SNP's which stands for Single-nucleotide polymorphisms. SNP's are the main force behind DNA and what gives it it's genealogical value. When two individuals have enough matching SNP's in a row, this becomes a matching segment. The more matching SNP's there are, the bigger the segment is. If a segment is big enough (bigger than 15cm's), it is safe to assume the two individuals share that segment because they both descend from a common ancestor who passed on that segment of DNA to both testers. The more matching segments there and the bigger they are, the closer two test takers are probably related. By testing a sample of a person's SNP's and then comparing them to everyone else in the database, it is possible to identify a person's genetic relatives. Most major companies will test 500-600k SNP's.

Autosomal DNA


Autosomal DNA (atDNA): This makes up about 95% of human DNA. It consists of 22 pairs of chromosomes and in each pair, one is from mom and one is from dad. The pairs of chromosomes are simply names 1, 2, 3, etc... 21, 22. They are mostly named by their size with chromosome 1 being the largest, chromosome 2 being the second largest etc. They are not perfectly named by their size, for example chromosome 22 is actually bigger than chromosome 21, chromosome 20 is slightly bigger than chromosome 19 etc. This is because as our understanding of DNA grows and improves, some chromosomes turned out to be a little bigger or smaller than we initially thought.

Autosomal DNA is the most important and most commonly tested type of DNA. A child will have exactly half of their autosomal DNA from each parent. However, a child will usually not have exactly 25% from each grandparent. A child could have 20% from one grandparent and 30% from another grandparent for example. This is because each child is randomly given half of their parent's DNA. When a new sperm or egg is formed, the pairs chromosomes in the parent line and exchange information, meaning segments are randomly cut out and switch places with each other to form new chromosomes that are a mixture of the previous ones. The child is then given one chromosome from each pair and the other is discarded. This happens in both parents so that the child receives one full set of chromosomes from each parent.

Y-DNA
Y-DNA: The term Y-DNA refers to the Y-Chromosome. There are 22 pairs of autosomal DNA. The 23rd and final pair are the sex chromosomes which come in two variants, X, and Y. Females have two X chromosomes, and males have an X and a Y. This is the second most valuable type of DNA. Although females do not have Y-DNA, they can get the same information by testing a close male relative such as a father or brother.

Mitochondrial DNA

 * Mitochondrial DNA (mtDNA): Mitochondrial DNA is unique. The rest of human DNA is located in the nucleus of the cell and is divided into chromosomes. Mitochondrial DNA on the other hand resides in the cell's mitochondria (the part that provides most of the cell's energy) and it is connected in a circle just like bacterial DNA. It is also the smallest portion of human DNA being about only 16,000 base pairs long. In other words, it is about one third the size of the smallest chromosome. These unique properties cause mitochondrial DNA to be have a special place among genetic genealogists. One advantage of mtDNA are that because it resides outside the nucleus, it can only be inherited from the mother. Sperm only contains a cell's nucleus and anything outside of that only comes from the mother's egg. This means that it does not go through recombination and testing your mtDNA can reveal information about your ancestor's on your direct maternal line. The other major advantage to mtDNA is that it decomposes slower than the rest of your DNA so it is more likely to be used for solving cold cases when the person of interest is no longer alive to test. It was by using mtDNA that the remains of Richard III were conclusively identified, for example.

One major disadvantage to mtDNA is that it mutates at a slow rate. A person whose mtDNA perfectly matches yours could be related through a common ancestor that lived anytime within the past 500 years.

Why use it in family history research?
Some of the reasons you may want to use DNA in your family history research:


 * Break down a brick wall where paper records may not exist to solve the problem
 * Confirm the relationship between two people or families
 * Learn about deep ancestry and ethnicity
 * Locate the biological parents of adoptees or people who don't know their parentage
 * Verify ancestral lines found through paper records

DNA testing risks
May disclose information you weren’t expecting such as:


 * Adoptions
 * Illegitimacies
 * Non-paternal events (NPEs; where parentage may be unexpected)
 * Name changes

DNA companies
The companies listed below provide ethnicity results and match lists


 * FamilyTree DNA - began in 1999
 * Autosomal (called their Family Finder test)
 * Y-DNA (37 markers through 700 markers with paternal Haplogroup)
 * mt-DNA (with maternal Haplogroup)
 * 23 and Me - began in 2006
 * Autosomal (with paternal and maternal Haplogroups)
 * GedMatch - began in 2010
 * Autosomal. Unlike the other companies, GedMatch does not sell DNA kits. However, you can upload your DNA results from any other company
 * AncestryDNA - began DNA in 2012
 * Autosomal
 * MyHeritage - began 2016
 * Autosomal
 * Living DNA - began 2017
 * Autosomal (with paternal and maternal Haplogroups)
 * For more information, go to Hiring a DNA Testing Company Wiki article.

Online Classes

 * FamilyTree DNA courses
 * GeneTech at FamilySearch
 * ISOGG Courses (International Society of Genetic Genealogy)
 * ISOGG Courses (International Society of Genetic Genealogy)

Additional information

 * Hiring a DNA Testing Company Familysearch Wiki page


 * Wiki of the International Society of Genetic Genealogy (ISOGG)

Facebook Groups

 * 23andMe Newbies - This is a group for those who are beginning genetic testing with 23andMe and discussing genealogy and health.
 * Africana Genetic Genealogy Consortium - This is a group for advanced-level exploration and discussion of African DNA research.
 * Ancestry DNA for Dummies - This group is to help understand Family research using DNA.
 * Autosomal DNA - This group talks about geographical and historical origins of your genetic markers.
 * DNA Detectives - From their Facebook group "The DNA Detectives group is focused on bringing together volunteers with genetic genealogy and searching experience with those seeking biological family -- adoptees, foundlings, donor-conceived individuals, unknown paternity and all other types of unknown parentage cases, near or far. This group is for members helping members and self-education."
 * DNA Tools - This group is for those interested in genetic genealogy DNA tools. Main sites discussed are DNAGedcom, Gedmatch AncestryDNA Chrome Extension and 23++ as well as new ideas for tools.
 * International Society of Genetic Genealogy (ISOGG) - From their Facebook group The mission of the International Society of Genetic Genealogy is to advocate for and educate about the use of genetics as a tool for genealogical research, and promote a supportive network for genetic genealogists."

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