B chromosome

B chromosomes (also known as supernumerary or accessory chromosomes) are additional to the normal basic chromosome set (called A-chromosomes). B chromosomes are 'extra' dispensable segments of DNA that do not recombine with the A chromosomes of the regular complement. B-chromosomes occur widely in flowering plants occurring in over 1000 plants and also in at least 260 animal species. Supernumerary chromosomes lacks functional genes, and feature an irregular, non-Mendelian, mode of inheritance.