Someone stated that the communication speed is currently about 160 bits per second, so 20 bytes per second.
Voyager is now 1 light day away, so the signal is 86400 seconds long, since radio waves travel at the speed of light. The signal can then fit a backup of 1.7 megabytes.
20 bytes x 86400 seconds = 1.7 Mb (SI units)
This is enough to fit the entire memory bank of 26 Commodore 64s in a one way trip from the Earth to Voyager. If Voyager then returns the signal, you can simply double this.
So about 2 floppy discs. 💾 💾
I don't think Downs works like that.
It's already being removed, since people choose abortion over downs and since people with Downs don't have children (normally).
It is not hereditary. It's an error or mutation that can occur for anyone. The chances are higher the older the parents are.