Genetic Genealogy For Beginners – Chapter 2


 Basic Concepts

There are two basic concepts that form the foundation of Genetic Genealogy. (

We humans inherit several “forms” of DNA, each of which can help genealogists research and confirm or reject different portions of a family tree. The DNA types are:

  • Mitochondrial DNA (mtDNA) found outside of the cell nucleus in tiny organelles called mitochondrial: (mitochondrion being the singular form);
  • Autosomal DNA (atDNA), which is composed of chromosomes 1-22 found in the cell nucleus, and

The sex-determining chromosomes, Y-DNA and X-DNA, also found in the cell nucleus.

The twenty-two autosomes and the X and Y chromsomes collectively are called nuclear DNA, as they are contained within the nucleus. 

Diagram of a human cell

The cell, the basic unit of life, uses genetic material called DNA to control the vast majority of its functions. DNA (short for Deoxyribonucleic-acid) is a component of the cell that carries a set of instructions development and operation of all living things. When two or more humans share segments of DNA, there is or was a shared common ancestor that lived in the past that connect those humans. Note: For African-American’s, DNA matches may not be readily identifiable, showing the real ancestor by surname; as migration occurred; name’ changes after the Civil War, forced name changes by slave owners, post traumatic stress disorder from slavery, adoptions by families of  children, lost of parents by hanging, jail and diseases from working in the fields and many other health related illnesses such as high blood pressure and cholesterol.

A very small percentage of DNA comprises genes, short segments of DNA that are used as the blueprint (map) to create a protein or an RNA (ribonucleic acid) molecule. A molecule of DNA is composed of a string of millions of smaller units called nucleotide. Together, two intertwined DNA molecules interact to form a single double-helix structure called a chromosome in the nucleus, or control center of the cell. A normal human cell has ninety-two long molecules of DNA that pair up to form forty-six double-stranded chromosomes. Each of these, in turn, forms a chromosome pair with another similar but not identical chromosome, to create twenty-three different chromosome pairs.

  • Nucleotide – The building block of DNA, it comes in four types that pair up in specific ways: Adenine (A), Cytosine (C), Guanine (G) and Thymine (T)
  • DNA (Deoxyribonnucleic acid) – A double-stranded molecule comprising two entwained strings of millions of different nucleotides
  • Gene – A region of DNA along a chromosome that encodes for a functional product such as a protein
  • Chromosome – A highly organized double helix of two DNA molecules
  • Chromosome Pair – Two complimentary chromosomes, one inherited from each parent

Double Helix courtesy of Danny Lela of the National Human Genome Research Institute access Dec. 2016

Chromosome chart courtesy of Darryl Lela of the National Human Genome Research Institute access Nov. 2016. This is called a Karyogram, which is all of the chromosomes of the human cell arranged in pairs in a numbered sequence from longer to shortest.

Note: Remember that the Mitochondria is outside of the nucleus. mtDNA and is not shown in this graphic.

The more DNA you share with someone, the more closer you are to that person. 

More on this and other topics in Chapter 3

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