If they have wings it could be that they all have wings. Or if they all have the same eye color it could be that. But that depends on their alleles.
Answer: a thrombus
A thrombus may also form in your heart
space radiation may place astronauts at significant risk for radiation sickness, and increased lifetime risk for cancer, central nervous system effects, and degenerative diseases. ... Astronauts are exposed to ionizing radiation with effective doses in the range from 50 to 2,000 mSv.