How is it that my aunt was born with one vertebrae missing then 5 yrs later, my mom was born w/ an extra one?

Question

Can anyone explain this? I know that their mother wouldn't have the missing vertebrae hanging around in her womb for 5 years, because that's impossible, but this seems more than just a coincidence...

(In case you're curious; my aunt, 5 years older than my mom, with her one missing vertebrae, is short and always has neck & spine problems. My mom, with her extra vertebrae, is tall, and deals with scoliosis...)

Answer 1

This is purely hypothetical..I believe its a case of chromosomal translocation, which is an error caused during meiosis (gamete formation). This would caused one of the resulting cells to have a bigger chromosome than another cell from the same division. What could have happened is that the portion of the chromosome with the gene encoding for the last vertebrae, could have been translocated to its homologous counterpart. By coincidence, your grandmother got pregnant from both of these eggs (i would say that this occurs in all her gametes). This caused your mother to have two copies of the same gene, therefore, two last vertebrae, while your aunt has a missing copy of the gene, hence a missing vertebra.

Answer 2

It doesn't have to be coincidence. It is quite possible that your grandmother or grandfather had some kind of genetic or chemical irregularity which had a tendency to modify vertebrae count in their children. I'm not a medical expert so I wouldn't know if there exists any kind of genetic setup in particular that can do this. On the other hand, it's also possible that it IS in fact just coincidence. The one thing we can be sure of is that the extra vertebrae did not somehow go from one baby to the other through time; this is about as likely as your dreams being supernatural omens, or as the Moon being made of green cheese, which is to say not very likely.

Answer 3

It is one of those examples of meristic variations in humans.
Nothing very unusual.