Y-Chromosome Testing

The Y- Chromosome is found only in males and is always found paired with an X-chromosome.  The Y-Chromosome is the chromosome which determines sex and is always found with an X chromosome.   In issues relating to paternity, paternal lineage and relationship testing it is the sex determining region Y (SRY gene) that is analysed.  You may find more information about this on DNA Relationship Testing.  The Y chromosome constitutes around 2% of the total DNA found in cells.  The Y-chromosome contains information about sperm cell development, and thus missing parts of the chromosome means that fertility is affected.

The Y chromosome along with the X is the sex-determining chromosome that defines the sexual development of a fetus. The difference between a male and a female is the Y chromosome, whereby females are XX and males are XY. As the second X in women is responsible for having children and the development of the female genetalia, the Y chromosome in males is also responsible for procreation. It encourages testicular development and male fertility.

The Y chromosome is passed on from father to son and is accountable for approximately 2% of the total DNA, spanning across around 58 million base pairs of chromosomes. Males usually have 23 pairs of XY chromosomes. There are certain conditions which directly affect Y chromosome expression and these include:

  • XYY syndrome males who inherit an extra Y chromosome
  • Jacobs syndrome
  • Klinefelter syndrome
  • Intersex conditions

A male’s sperm cells are heterogametic. ‘Gametic’ comes from the word gamete which is another word for sperm cells. ‘Hetero’, meaning different, in this case refers to the X and Y chromosomes that are produced by males. Males produce two types sperm (gametes), a Y chromosome and an X chromosome.

When testing male relatives within a family, a Y-STR test may be performed in order to determine whether there is a biological relation. There are several reasons for wanting to test the Y chromosome including: immigration, adoption, sibling matches among others.