Transmission might seem to entail some tangible thing that is being passed from sender to receiver. For example, inheritance is some property or money that parents leave for–or transmit to–their offspring. However, people now also speak of heredity as a transmission of traits or characteristics, even though the egg and the sperm, which are transmitted, have none of traits in question, e.g., height, aggression, blue eyes, etc.
In my writing about nature-nurture science, I usually note something to the effect that
as a starting point, the potential for confusion in the varying uses of the term “genetic” diminishes if genetic is reserved as an adjective in reference to factors that are transmitted from parents to offspring and whose presence can, in principle, be observed. In a similar spirit, “environmental” can be taken to refer to measurable factors, which can range widely, say, from average energy intake to maltreatment as a child.
I use factor in a colloquial sense as a bland word with few connotations. Read: “thing” or “entity.” But I have often had readers ask why I don’t talk about “traits” or “characteristics.” They are quite comfortable with the idea that physical traits and personality traits can be transmitted. My guess is that the term became metaphorical — heredity is like transmission in that a germ cell is transmitted and it contains all the potential or instructions or information for the resulting organism that does show the traits. And then it became sufficient to think of the heredity being the transmission of the information and not to unpack just how information becomes, through development, the organism that does show the traits. (This has been the subject of Susan Oyama’s critiques such as the Ontogeny of Information.)