An xxy or an xo person can occur when the female producing an egg with or chromosomes. the male produces the normal sperm of x or y.

An XXY or an XO person can occur when the female has nondisjunction, producing an egg with two X or no X chromosomes. 

When there is nondisjunction in meiosis division of the gamete, the X chromosome of the egg might fail to separate, resulting in an egg with XX chromosome and other egg without X chromosome. When XX egg fertilized, it will become XXY and when O egg fertilized it become XO.

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.