What is the Chromosome Browser (Shared DNA segments)?

The human genome consists of 22 pairs of chromosomes (also called autosomes, numbered from 1 to 22) and 1 pair of sex chromosomes (also called heterosomes, identified by X and Y). Each pair of chromosomes contains a paternal copy and a maternal copy.

In the Chromosome Browser, each pair of chromosomes shows up as an horizontal bar which length depends on the total number of bases they contain. The Y chromosome does not show up in this chart because it is not used for the identification of shared DNA.

Each pair of chromosomes can contain up to 3 different pieces of information:

• The absence of shared DNA segment;

• The presence of a half-identical shared DNA segment, which means that the DNA you share with your relative is present on only one copy of the chromosome, thus inherited from only one of your parents;

• The presence of a full-identical shared DNA segment, which means that the DNA you share with your relative is present on both copies of the chromosome, thus inherited from both of your parents.

In which cases do you share full-identical DNA?

• Between siblings: identical twins share only full-identical DNA, and siblings share only a part of their DNA as full-identical;

• Within a family: first cousins whose parents belong only to two distinct siblings have a small part of their DNA as full-identical. Note that inbreeding within a family or population can also lead to the appearance of full-identical DNA segments.

The longer the shared DNA segment is, the closest the relationship is and the higher the chance to find a common ancestor is. The smallest the shared DNA segment is, the more distant the common ancestor is and the lower the chance to find it is.

You can download these data by clicking “Export data to CSV file”.