The Y Chromosome
It's a guy thing!

Elementary genetics teaches that a human egg with an X chromosomes becomes a female embryo when a sperm gives it an X chromosome to make an XX pair and a male embryo when a sperm gives it a Y chromosome to make an XY pair. Thus the Y chromosome is passed down generations only through the male line. Recent research has followed the human Y chromosome back to Africa.

For a booklet describing using the Y-chromosome in genealogy see

You might want to read the following articles about the Y chromosome:

Mutations (polymorphnisms) on the Y-chromosome are used to determine many interesting facts about relationships among humans and about human migration. The mutation locations are called markers, the most important of which are Single Nucleotide Polymorphisms (SNP) and Single Tamden Repeats (STR) (also called microsattelite) or DNA Y-chromosome Segment (DYS).

Information about where some of the DYS markers are located on the Y-chromosome.

Information about the Y-chromosome markers (STRs).

Books about the Y-chromosome: