Sugar
Phloem transports sugar from a sugar source to a sugar sink.
The factor that is responsible for the phenomenon of the blood group B being almost absent in Native Americans whose ancestors arrived in very small numbers about 10,000 years ago would be called the 'founder effect'.
If you are filling out a punnet square it will look like the photo below but it will produce YySS yySS YYSs YYss YySs and yyss