Therefore, all of us, male and female, get our mitochondrial DNA from our mother's fertilized egg. Like the Y, mitochondrial DNA doesn't recombine. It is passed down unchanged from mother to offspring. Males can't pass it on to their offspring, so it goes strictly through the maternal line, just as the Y chromosome goes through the paternal line. We only know that their genes have met in us.
Mitochondria provide the energy that drives that cell.
Exactly what it is that the Y chromosome does is a long-standing mystery, only slowly being revealed by recent genetic discoveries. The main function of the Y is to switch the growing embryo from female, the default anatomy, to male. It does this by creating testes, which then set off a hormonal and physical chain reaction that creates a baby boy. Until recently, geneticists saw the Y as a DNA desert. It took 30 years of intensive searching before the testis-determining gene was finally located on the Y chromosome in 1990.