Assuming that a girl slept with an invisible guy, what kind of child can she have, and what sperm will her father have (visible or not)?

Which one will be born will depend on which gene will appear in the first child. Let's call the gene responsible for invisibility d, and for visibility D, since, nevertheless, the gene of visibility will be dominant, because there are more visible ones (although who knows, invisible ones are not visible).

If you have no invisible people, then most likely you have two alleles D. And he has two ds, since if he had D, he would be visible.

Go ahead, your offspring will be DD: 2Dd: dd

Accordingly, if you give birth to 4 children, three of them will be visible, but they will be carriers of the recessive invisibility allele. And you won't see one child, since he will be invisible.

But the discharge will be invisible, otherwise drops of sweat, blood from the wound, sperm, urine - you won't see all this, as if it were visible , the dermis would have to be invisible and at the same time not transmitting the visibility of other fluids / tissues and other things (this is due to the reflection of light, I do not understand this, so I cannot answer in more detail).

Thanks for the answer. I decided to ask on this site, because after conducting a small social survey among my friends, I was able to identify several assumptions. The first is that the sperm will be visible due to the fact that it leaves the invisible zone of the guy's body, the second is that the sperm will be invisible, because all body secretions (including sweat, urine, etc.) are also invisible. About the birth of a child, we could not get a more or less clear answer

Ideally, the answer to this question can only be found out experimentally. Find several (preferably at least 20) guys (invisible). Have sexual intercourse with them - at least twice - the first time at any time using mechanical means of protection (condom). Send sperm from these funds to the laboratory to determine its transparency. This will answer the second question. To answer the first - you have to re-engage with each of these guys on ovulation day - you have to take significant breaks here, but science requires sacrifice. And each descendant from these links - also ask to check in the same laboratory for transparency. Unfortunately, I cannot imagine other ways to find out the answers to your questions ... ((