Question

1. Colchicine (a chemical) inhibits separation of sister chromatids in mitosis. Cultured plant cells can be treated with colchicine during one cell cycle, then exposed to the right hormones and induced to develop into small tetraploid plants. The fruit of plants is larger and seeds smaller and softer as chromosome numbers increase, so this method is used to produce more desirable fruit in some cultivated crops. A certain crop plant is made tetraploid this way.

   1. If the original haploid number was ? = 13, how many chromosomes are present in somatic cells of the tetraploid crop plant?

   2. Will the tetraploid crop plant be fertile? Why, or why not?

Answer 1

the haploid number of chromosomes= 13

number of chromosomes in the tetraploid=413= 52

( haploid cells have only one set of chromosomes, tetraploid cells have 4 sets of chromosomes, so the number of chromosomes in the tetraploid is =413= 52 )

polyploid plants odd number of chromosomes sets are not fertile example triploid, pentaploid plants are not fertile.

gametes are produced by meiosis, during meiosis I the homologous chromosomes pair up, if the ploidy is 3n or 5n there will be one set of chromosomes that cannot pair with the homologous chromosome, so the meiosis cannot occur in cells with the odd number of chromosome sets.

if the plant is tetraploid, the number of sets of chromosomes is 4n, that is the cells have even number of sets of chromosomes, so these cells can undergo meiosis, (during meiosis I the homologous chromosomes can pair up) and produce diploid gametes so the tetraploid plants are fertile.