What are the possible genotypes of the off spring from the cross above (bb, bb, bb, bb)?

Bb, BB, bb
I hope I have helped you. The way I figured this out is by drawing a Punnet Square and working out the cross.

BB - homologous
Bb - heterozygous
bb - recessive

answer: - b cells

explanation: -

there are many types of white blood cells present in our body. one such class of white blood cells are the lymphocytes. the b cells belong to the lymphocyte class of wbcs. the b cells perform their action against the pathogen by producing specialised proteins called as antibodies. these antibodies are produced as and when the b cells encounter pathogens in response to the antigens present on the surface of the pathogen. these antibodies bind to the antigens present on the pathogen and then, target them for destruction by other cells of the immune system.

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.