In an attempt to answer this question honestly, I would say that breast and penis size have variable heritability, meaning that the “amount” of the phenotype offspring will have will vary, even with the same parents. The amount of heritability is very high for some things, and very low for others.
Now that I’ve just found my genetics textbook:
Heritability is the porportion of a population’s phenotypic variance that is attributable to genetic differences.
(Snustad, Simmons, Principles of Genetics 2nd ed.)
Envirnmental factors and genetic factors are both reflected in the heritability values. The value of heritability may also differ among populations, due to different genes and different environmental effects.
So back to what I was saying, its high for some traits, low for others.To give a couple of examples:
Stature in humans: 0.65
Milk yeild in dairy cattle: 0.35
Litter size in pigs: 0.05
Egg production in poultry: 0.10
Tail length in mice: 0.40
Body size in Drosophila: 0.40
There are a couple types of calculations one can do to predict the phenotype of the offspring, which I don’t feel like going into, but just by looking at the above values, one can see that if you’re a human, your stature will resemble that of (both)your parents quite a bit (ie., somewhere in between). If you’re a pig, the number of babies you’ll have at one time has not much at all to do with that of you mother or grandmother, etc.
So, back to the OP, assuming that penis and breast size are not x/y linked and that that doesnt come into play (I’m thinking there are probably many genes involved), then variable haritability kicks in, and doesn’t necessarily mean that small-breasted women will have small-breasted daughters, and large-penised men will have large-penised sons, and vice versa.
Does that make any sense?
Now back to the jokes…