If you’ve just entered the world of genetic genealogy, you may have heard many terms tossed around and haven’t been quite sure what everything meant.
In this post, we’ll set the record straight by defining the most important terms in DNA.
DNA is an acronym for deoxyribonucleic acid: a substance that exists in almost all organisms and constitutes an “instruction manual” for all the cells in the body on how to form that organism. This substance is inherited from our biological parents: around 50% each from the mother and the father.
Studying our DNA can unlock many secrets about us, our traits and tendencies, our health, and our ancestors, as well.
Nucleotides are the building blocks of DNA. Each nucleotide consists of a base, a sugar molecule, and a phosphoric acid molecule. There are four chemicals that constitute bases: adenine (A), thymine (T), guanine (G), and cytosine (C). The bases pair with each other — A with T and G with C — to constitute a string of DNA.
Most human cells contain 6 billion nucleotide pairs — 12 billion nucleotides altogether. That’s a very long string of DNA! To keep all of it orderly and ensure that the cell division process occurs with minimal error, the DNA is organized into a number of thread-like “packages.” These packages are called chromosomes.
The human genome contains 23 pairs of chromosomes (46 chromosomes altogether). There are two types of chromosomes in humans: allosomes, also known as sex chromosomes or X and Y chromosomes, which are connected to the individual’s biological sex, and autosomes (body chromosomes), which are not.
Autosomal DNA is the DNA found in the autosomes mentioned above. An autosomal DNA test, such as the MyHeritage DNA test, examines only the information on those 22 chromosomes.
Y-DNA is the DNA found only on the Y chromosome, which only appears in biological males. Women’s allosomes consist of two X chromosomes, while men’s consist of one X and one Y chromosome. Examining the Y-DNA can give us unique information about a biological male’s paternal line.
mtDNA stands for mitochondrial DNA: DNA located in a part of the cell called the mitochondrion. Most of our DNA is located in the nucleus, or center, of a cell, but there is a certain amount that can be found in the mitochondrion. Mitochondria are almost exclusively passed from mother to child, so examining your mitochondrial DNA can give you unique information about your maternal line.
A genetic mutation is an alteration in the DNA sequence that occurs during the process of DNA replication: when the DNA copies itself to turn a single cell into two. Mutations can be a “fluke” that occurs in a specified group of cells within a single individual, or a permanent change that is passed down to the next generation through that individual’s reproductive cells (sperm or eggs).
Sometimes these hereditary variations result in changes to observable traits, such as eye or hair color, but most of the time they don’t. However, it is through analyzing these variations, even the ones that don’t cause observable changes, that scientists can determine things like your ethnic background and your susceptibility to various health conditions.
Genes vs. Alleles
A gene, as defined above, is a unit of inheritance in our DNA, while an allele is a variant of a given gene. Variations in our DNA occur through a natural process of mutation, as described above.
In plain English, a haplogroup is a genetic sequence found in multiple individuals who have a single common ancestor. More specifically, it’s a group of haplotypes, which are groups of alleles inherited from a single parent. Haplogroups are most relevant when discussing Y-DNA and mtDNA, since these sections of DNA are inherited only from the father or the mother and never mix, so variations inherited within these sections generally remain intact.
A genetic marker is a gene or sequence of DNA that has a known location on a chromosome, and can be used to identify individuals or species.
A centimorgan is a unit of distance between chromosome positions, used to measure sections of DNA that are identical in two individuals. The longer a section of identical DNA — the more centimorgans of DNA they share — the more closely related those individuals are likely to be.
DNA Match Clusters
“Clusters,” in the context of DNA Matching, are groups of a given individual’s DNA Matches who also match one another. Looking at your DNA Match clusters can help give you clues as to how you are related to unidentified DNA Matches. For example, if you don’t know how you’re related to a certain match, but you locate him or her in a cluster together with your mother’s first cousin, you know you are probably related to that mystery match through your mother’s side. MyHeritage’s AutoClusters makes it very easy to view and analyze your DNA Match clusters.