Information at a Glance – Chromosome Number of Onion
|
Species |
Onion (Allium cepa L.) |
|
Ploidy |
Diploid, 16 (2n = 16) chromosomes |
|
Chromosome number |
16 or 8 pairs Diploid meiocyte = 16 chromosomes Reproductive cells = 8 chromosomes |
Ploidy of Onion
Onions are long day plants when it comes to bulbing; the short day and low-temperature conditions are needed for vegetative growth. Most frequently, onion is a perennial or biennial plant; however, typically, it is treated as an annual one that is harvested in their first growing season. A normal and healthy cell of onion has 16 (2n = 16) chromosomes.
Onion cells comprise 8 chromosomes. The cells of onions are meiocytes that are diploid (having two sets of chromosomes). Diploid cells or meiocytes have 16 chromosomes. When the meiocytes divide, forming gametes, the chromosomes become half (8). As a result, the number of chromosomes in the gametes of onions are 8 in number while the chromosome number in diploid cells of the onion is 16.
Chromosome Number of Onion
Onion is a flowering plant, an angiosperm. The plant body of angiosperms mainly is sporophytic. Hence, in their plant body, all cells are diploid in nature; that is to say, there are two sets of chromosomes. The chromosome number is 2n = 16.
Meiocytes, on the other side, are a type of cell occurring at the time of reproduction. In the organisms which take up the sexual mode of reproduction, fertilization forms the main and primary event. Hence, both the male and female gametes are to fuse through the process of syngamy or fertilization. Thus, the zygote is obtained, which goes on to form the embryo giving rise to the new offspring.
Gametes are formed as part of the pre-fertilization process through the process of gametogenesis. In sexual reproduction, meiocytes or gamete mother cells are seen in the primary sex organs (gametogenesis occurs here). One of these cells in the primary sex organ takes up the role of the gamete mother cell; in these cells, meiosis or reduction division occurs to produce haploid gametes from the diploid cells.
To summarise, in meiocytes, the process of reductional division or meiosis has still not occurred and is about to occur. Hence the chromosome number is the same as the other cells of the body. Consequently, the gamete mother cell stage has the normal diploid chromosome number.
As a result, the normal chromosome number in onions is 16. In gametes, the content is halved, and hence it would be 8.
This was a brief on chromosome number of onions. Explore related articles at NEET BYJU’S.
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