What is the difference between autosomes and sex chromosomes?

When you’re conducting genetic research of any kind, knowing how to properly understand DNA reference terminology is key. While some genealogical terms may seem confusing, don’t worry, this stuff is not as complex as you might think. Below we will clear up the difference between sex chromosomes and autosomes to better help you understand how DNA works how these terms apply to genetic testing.

Autosomes vs Sex Chromosomes

Every living organism has cells and chromosomes. Chromosomes are found in the nucleus of a cell and are mostly classified as autosomes. The number of chromosomes in each organism varies, though human beings all generally have 46 chromosomes which are split into 23 pairs. You receive half of those from your mother, and the other half from your father. Out of all of these chromosomes, 2 are sex chromosomes (XY or XX) and the other 44 are autosomes.

• Sex Chromosomes
Sex chromosomes are the chromosome in a cell that determine gender. Humans have two sex chromosomes. These are called the X chromosome and the Y chromosome. If you’re a woman, you will have two X chromosomes (XX). If you’re a man, you’ll have an X and a Y chromosome (XY). All of the egg cells of a mother contain an X chromosome, and all sperm cells of a father contain either an X or a Y chromosome. This means that the sperm from the male determines what gender will manifest at an egg’s fertilization. Put simply, your gender determination comes from your father’s sperm and is not determined by your mother’s mitochondrial cells in any way.

• Autosomes
An autosome is defined as any chromosome that isn’t a sex chromosome. So, apart from the two sex chromosomes which determine your gender, all other of the other chromosomes you have are autosomes. You have 44 autosomes in 22 pairs which are numbered 1-22.

How does this apply to DNA testing?

When it comes to DNA testing, whether you have a Y sex chromosome or two X sex chromosomes will determine the types of DNA testing that you’ll have access to. Y-Chromosome testing (Y-DNA testing) is only available to individuals with a Y chromosome, otherwise known as men. Mitochondrial DNA testing (mtDNA testing) is available to those with an X chromosome, so it works for both men and women. Autosomal DNA testing is also available and works for both men and women.

Y-DNA testing traces DNA through the father’s line, or, patrilineality. Women who wish to have their paternal line traced can ask their father, brother, or a male cousin to complete a DNA test on their behalf. Mitochondrial DNA testing traces the mother’s lineage, or, matrilineality. Autosomal DNA testing identifies common DNA related genetic markers and patterns.

You have 44 autosomes and 2 sex chromosomes making up a total of 46 chromosomes in 23 pairs. Autosomes are used in autosomal DNA testing while sex chromosomes are used for mtDNA testing and Y-DNA testing. As you can see, while these terms may initially seem confusing, things clear up once you understand their meanings and applications to the DNA testing process.