Chromosome Number

We have seen that the nucleus of each cell of the plant, with the exception of the sex cells, carries two sets of chromosomes; one inherited from the father and one from the mother. The basic chromosome number of the sex cells in which each chromosome is different and carries a different set of genes is the haploid number. The cells of the body of the plant (somatic cells) usually carry double this number and are diploid . However, plants with more than two sets of the haploid number are not uncommon and are said to be triploid (3×), tetraploid (4×), pentaploid (5×), hexaploid (6×), heptaploid (7×), octaploid (8×), decaploid (10×), dodecaploid (12×), or referred to collectively as polyploids . For example ( Table 2.1 ) several cultivars of apple and pear are triploid, leek tetraploid, plum hexaploid, strawberry octaploid and black mulberry highly polyploid. Sometimes the somatic cells may not contain an exact multiple of the haploid number so then there are a few extra or fewer chromosomes; these are aneuploids .