![physical exam stories boys gay nifty physical exam stories boys gay nifty](https://i.ytimg.com/vi/06VV4oGwr4M/hqdefault.jpg)
If size was entirely from the Y chromosome, men with the same father would all have essentially the same size penis. Considering genetic brothers can have vastly disparate penis sizes, some experts suspect that there’s more influence from a mother’s two X chromosomes. If you have a strong memory of seventh grade health class, you’ll remember that those given a Y chromosome start to grow a penis.īut when it comes to penis size, scientists aren’t sure which parent has more of an influence. At eight weeks, genitalia starts to develop and differentiate.
![physical exam stories boys gay nifty physical exam stories boys gay nifty](https://64.media.tumblr.com/690f504d748a13ff3762fcbe962c3809/tumblr_ndtov7vVae1toa9dro4_400.jpg)
The fetus doesn’t have a penis for its first seven weeks in the womb. “So you can’t entirely blame your mom for your small penis.” What Determines Penis Size? Although most of the genes responsible for penis size live along the X chromosome, “there are some genes in the Y chromosome that have links to penile lengths and size,” urologist Jamin Brahmbhatt, MD, tells Fatherly. Studies suggest that penis size is a joint genetic effort between both parents. But what determines penis size? Is penis size genetic? And how does a person end up with a micropenis? As it turns out, these questions - as well as questions of where penis genes come from and how much the environment plays a role in who is well-endowed and who isn’t - aren’t exactly straightforward.