Parasitism is an association in which one organism, lives on another, the host, deriving benefit from it and causing harm to it.
The tapeworm here is a parasite and it lives inside the cat's(host) body where the tapeworm is specialized for its mode of life. It survive and reproduces very well without needing another specie because it is a hermaphrodite. It causes loss or poor development of unwanted organs such as the digestive, sense organs and muscles. Its long flattened body also provides a large surface area for absorption of nutrients too.
As the offspring inherits one allele from each parent, it will obtain only the B allele from the female mouse and either the B or b allele from the male mouse. Hence possible offspring genotypes are BB or Bb with 0.50 probability each (each probability of either genotypes being present in the offspring).
