Human DNA is composed of 23 pairs of chromosomes. Half of your DNA comes from each of your parents. Chromosome pairs 1 – 22 are called autosomal DNA. These genetic pairings do not differ for males and females.
The 23rd chromosome differs according to gender. Men receive a Y-chromosome from the father and an X-chromosome from the mother. Women receive one X-chromosome from both father and mother.
This color coded chart shows possible combinations for a male. The male will inherit ONE of these X-Y pairs.
In a family with only male children, the X-chromosome from the paternal grandmother is essentially lost. Her genetic contribution continues to be expressed through autosomal and mitochondrial DNA (see explanation below).
Females inherit one X-chromosome from each parent. The diagram shows possible combinations from each parent but only one X-X pair is inherited by female offspring.
In addition to the X-chromosome, mitochondrial DNA is passed on from mother to both male and female children. Mitochondrial DNA resides outside of the cell nucleus within the mitochondria. mtDNA is NOT part of the 23rd chromosome.