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我们一般食用的普通西瓜是二倍体（2n=22）,用秋水仙素处理普通西瓜的幼苗,染色体加倍,就可以得到四倍体（4n=44）。再用四倍体植株作为母本,用二倍体植株作为父本,进行杂交,就能在四倍体植株上结出三倍体的种子（3n=33）。三倍体的种子长成的三倍体植株,由于在减数分裂时,染色体联会、组合和分离很不平衡,也很不完备,因而不能形成正常可育性的生殖细胞。所以胚珠不能发育成为种子。但其子房在受到普通西瓜成熟花粉的刺激后,能正常发育成果实。无籽西瓜就是这样产生的。 无籽西瓜真的不结籽吗?吃过无籽西瓜的人都知道:无籽西瓜的果实里面有大量未发育不带硬壳白色的瘪子,但偶尔也有少量带硬壳的真正的种子。也就是说,无籽西瓜并非绝对无籽！这是为什么呢? 无籽西瓜属同源三倍体植株（3n=33）,其性母细胞在减数分裂时,同源的每三个染色体在第一次分裂前期联会时或组成三价体（三个染色体连在一起）或组成二价体（两个染色体连和单价体（一个染色体单独存在）。在后期时,二价体分离正常,单价体一般随机进入细胞两极的一极,而三价体一般是两条进入细胞的一极,另一条则进入细胞的另一极。据观察,对于同源
We generally eat ordinary watermelon is diploid (2n = 22), with colchicine treatment of ordinary watermelon seedlings, chromosome doubling, you can get tetraploid (4n = 44). By using tetraploid plants as the female parent and diploid plants as the male parent, crosses were made and triploid seeds (3n = 33) were produced on tetraploid plants. Triploid plant-grown triploid plants, because of meiosis, chromosome association, combination and separation is very unbalanced, is not perfect, and therefore can not form a normal fertile germ cells. Therefore, ovules can not develop into seeds. However, its ovary by the normal watermelon mature pollen stimulation, the normal development of fruit. Seedless watermelon is produced like this. Seedless watermelon does not really seed it? People who eat seedless watermelon know: seedless watermelon fruit there are a large number of undeveloped without hard shell white deflated, but occasionally a small amount of real seed with hard shell . In other words, seedless watermelon is not absolutely seedless! This is why? Seedless watermelon is a homeologous triploid plant (3n = 33), the sex cells in meiosis, homologous to each of the three chromosomes at the time of the first division of the early association or composition of three The voxels (the three chromosomes are linked together) or make up the bivalent body (the two chromosomes are linked to the monovalent body (one chromosome is present alone).) In the latter stage, the bivalent body is normal and the monovalent body generally randomly enters one pole of the cell’s bipolar , While the trivalent body is generally two into the cell pole, the other into the other cell pole.It is observed that for homologous