Question

You know the meaning of the word "diploid." Bananas are triploid. What do you suppose that means? Wheat is a hexaploid. What does that mean?

Triploid bananas are sterile — they reproduce only asexually. What problems do you suppose a triploid has in meiosis that might explain this? NOTE: Yes, I know it's easy to discover that nuclei must have an even number of chromosome sets to do meiosis. The question here is why?

Answer 1

Diploid means the cells have 2n number of chromosome, for examples in human 23 pairs of 2n chromosomes which means 2(23)= 46 numbers of chromosomes. Banana has triploid, 3n numbers of chromosomes hence for examples it has 11 triploid number of chromosome (11 (3) = 33). Similarly, Hexaploid means 6n number of chromosomes in organism.

   In general process of meiosis, diploid cell produces two haploid daughter cells. However in banana meiosis is not possible because the plant is triploid. Pairing of chromosomes occurred only between two homologous chromosomes to form a bivalent. Bivalent formation in metaphase of meiosis is an important step for production of haploid germ cells. However in triploid the chromosomes are not equally disturbed, one become bivalent and other become univalent or trivalent. Hence at the stage of the anaphase uneven numbers of chromosomes are distributed in each daughter cells (some are haploid and some are diploids etc). Additionally, one extra chromosomes has deleterious effect on cell division, as one extra chromosome contains extra copy of gene which altered the gene expression and affect the process of cell division at meiosis. So banana triploid plants remain sterile and reproduced only asexually.