Re: Do genes determine your penis size?

Dear Joseph,

Like all features of our anatomy, the size of the penis is ultimately 
judged by genes that were inherited from both our father, and mother. An 
example of such a genetic component can be found in cases of micropenis 
syndrome, in which slight changes in the sequence of a gene encoding the 
protein 5Alpha-Reductase Type 2 have been linked to abnormally small 
penis size, or even genital ambiguity. This protein is an enzyme which 
metabolises testosterone in the peripheral tissues, and would therefore 
be expected to play a more general role in growth and development. As 
such, it is unclear whether the role of the 5Alpha-Reductase Type 2 gene 
(or any other penis-size gene for that matter) is exclusively linked to 
the size of the penis. Moreover, specific dimensions, such as length or 
width are likely characterised by a complex interaction of genes rather 
that by one single gene.
Although environmental factors may also play a significant role in the 
final size of a developing penis, these effects are hard to study because 
of their subtlety, ontop of the invasive nature of studying a developing 
fetus. However, the size of a flaccid, relaxed human penis is 
considerably sensitive to cold temperatures. A drop in temperature can 
lead to the diversion of blood flow from appendages in an effort to 
conserve body heat, resulting in decreased flaccid size of the highly 
vascularised penis.

Hope that helps!