Education - Chromosomes - Characteristics

Chromosome Characteristics

Identification

Rice chromosomes are extremely small. Compared with the chromosomes of barley which belongs to the same Family Gramineae, rice chromosomes are approximately one-fifth to one-tenth of barley chromosomes (Fig. 2). Recent studies revealed that the rice genome consisted of 430 Mb while the amount of DNA of barley genome was as eight times large as the rice genome, making clear the correlation between the amount of DNA and the size of chromosomes.

Figure 2. Barley (left) and rice (right) chromosomes at the metaphase of somatic division. (at the same magnification)

Just before the somatic division, the chromosomes are the most shrinked. They are only 1 - 5 microns long and difficult to be identified. Therefore, the nuclei at the prometaphase and the end of prophase in which the chromosomes are from 3- 10 microns to 7 - 15 microns long are used for the karyotype analysis and the identification of chromosomes (Figures 3a and 3b).

Figure 3. The nuclei at the prometaphase (a) and the late prophase of somatic division. Figure 3b is the nucleus used for the construction of Figure 1b (2n=24+1).

For the detailed analysis, chromosomes at the pachytene of prophase in the first division are used (Figures 4a, b, and c). Not much difference in the pattern of chromomere configuration was found at this period among O. sative (AA genome), O. punctata (BB genome) and O. brachyantha (FF genome).

Figure 4. (a) Pachytene nuclei and (b) the late pachytene bivalents during the prophase at the first division of meiosis.