Y- Chromosome DNA or Y-DNA

Human sex is determined by the X and Y chromosomes. A female has 2 X-Chromosomes and a male has an X and a Y-Chromosome. When a child is conceived it gets one chromosome from its mother and one chromosome from its father. The chromosome from the mother will always be an X, but the chromosome from the father may be either X or Y. If the child gets the X she will a girl, if the child gets the Y he will be a boy.

This Y-Chromosome has certain unique features:

The presence of a Y-Chromosome causes maleness. This little chromosome, about 2% of a father's genetic contribution to his sons, programs the early embryo to develop as a male.

It is transmitted from fathers only to their sons.

Most of the Y-Chromosome is inherited as an integral unit passed without alteration from father to sons, and to their sons, and so on, unaffected by exchange or any other influence of the X-Chromosome that came from the mother. It is the only nuclear chromosome that escapes the continual reshuffling of parental genes during the process of sex cell production.

It is these unique features that make the Y-Chromosome useful to genealogists.

Y-DNA markers can be used to test relatedness to other males with the same surname. These Y-chromosome DNA markers are called DYS, short for DNA Y-chromosome Segment.

A string of DYS markers is called a haplotype. A haplotype (set of DYS markers) represents the genetic “signature” for a specific male line’s Y chromosome.

A haplotype can be used to predict a haplogroup, which is a major branch in the human family tree.

An example of a Y-DNA surname project is located at:


An example of a Y-DNA testing company is at:


Related items;

DNA, Y-DNA, Surname project, DYS