Human DNA is composed of 23 pairs of chromosomes. Chromosomes 1 – 22 are autosomes. These chromosomes are not differentiated by sex. Half of your DNA is inherited from your father and half from your mother. The autosomal DNA which comes from your father has the same number of genes as the DNA half which is inherited from your mother. This diagram does not distinguish between paternal-maternal pairs in chromosomes 1-22 because they contain same types of genetic markers.
Courtesy: National Human Genome Research Institute
Sex chromosomes reside in position 23. Genetic males have X-Y pair. Females have X-X.
Notice how the X chromosome is much longer in the diagram? The X-chromosome contains approx 900 genes while the Y-chromosome only contains 55. There is much more information encoded in the X-chromosome. Some genetic diseases such as hemophilia are passed via the X-chromosome.
This simple diagram illustrates how the Y-chromosome is passed from father to son. Only one of these X-Y pairs will be inherited by male offspring. A male possesses the same Y-chromosome as his father, his grandfather, and so forth. Using statistical analysis, researchers estimate that a common male ancestor lived about 150,000 years ago. Of course, the Y-chromosome in modern men is not exactly like the Y-chromosome of that ancient ancestor. Chromosomes mutate over time.
X-inheritance is a bit more complicated. Females have two X chromosomes. (In the diagram above, the female inherits ONE XX pair). The father contributes one X-chromosome to his daughter. That chromosome came from his mother. But from where did that X-chromosome originate? It could have come from either his maternal grandmother or maternal grandfather.
In addition to the 23 pairs of chromosomes in the nucleus of every cell, DNA also exists in cell mitochondria. This is called mitochondrial DNA or mtDNA. mtDNA is inherited from your mother. Just as Y-DNA is mostly unchanged from father to son, mtDNA is passed directly from mother to child (both male and female).
Analysis of Y-DNA and mtDNA provide insights into ancient people groups or haplogroups. Shared genetic patterns (or mutations) allow genetic researchers to trace ancestry to various ethnic groups and their geographic locations. Paternal (Y-DNA) and maternal (mtDNA) have separate haplogroups which are defined using letters of the alphabet.
My maternal haplogroup is K. It is found in approximately 6% of the population world wide but has a higher rate in Ashkenazi Jews as well as some areas of France and Belgium.