Inheritance of Baldness
A: Not necessarily. The old myth that male-pattern baldness is inherited from the maternal grandfather simplifies things way too much. A bald maternal grandfather may be one piece of the genetic puzzle, but your risk of male-pattern baldness depends on a much broader combination of genetic variants inherited from both sides of your family.
One key gene that researchers know a lot about is the androgen receptor (AR) gene, which is located on the X chromosome. Variations in and around this gene are associated with increased susceptibility to androgenetic alopecia. Because a man normally receives his X chromosome from his mother, this explains why researchers have historically focused on the mother's side of the family.
But this does not mean that the tendency toward baldness necessarily comes from the maternal grandfather. A man's mother has two X chromosomes: one from her mother and one from her father. She can pass either X chromosome to her son. So, a maternal grandfather can be relevant to a man's risk, but he is not the sole or necessarily the primary source of the genetic predisposition.
On top of that, the genetic contribution to male-pattern baldness is not restricted to the X chromosome. Researchers have identified susceptibility regions on other chromosomes, such as chromosome 20, and subsequent research has identified many additional genetic spots across the genome.
Because of this, the tendency toward male-pattern baldness can be inherited from either side of the family. Having a bald maternal grandfather may be associated with an increased risk, but having a non-bald maternal grandfather doesn't guarantee you're safe. By the same logic, having a bald father or other relatives with male-pattern baldness can provide relevant information about your family history.
To wrap it up, male-pattern baldness is hereditary, but it does not simply pass from the mother's father to her son. It is a complex genetic mix driven by multiple genes on the X chromosome as well as your other chromosomes. Together, these combined genetic factors control how your body responds to male hormones and how sensitive your individual hair follicles are to thinning out over time.
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See also:
Hair loss
Testing and treatments for genetic hair loss
Hereditary hair color and how parents determine a baby's hair.