In maize what would be the minimum number of meiosis to produce 100 grains ?

Question

Accepted Answer

The correct option is 4: 125

The core of this question lies in understanding the difference in gamete formation between the male and female reproductive structures in angiosperms like maize. To produce 100 grains (seeds), we need 100 successful fertilizations, which consequently requires a minimum of 100 functional female gametes (ovules) and 100 functional male gametes (pollen). The minimum number of meiotic divisions is the sum of the meiotic divisions required for both sets of gametes. For the formation of the male gametes, each microspore mother cell undergoes one meiotic division to produce four haploid microspores, and each microspore develops into a functional pollen grain containing the male gametes. Therefore, to get 100 pollen grains, we require $100 \div 4 = 25$ meiotic divisions in the anther. For the formation of the female gamete, each megaspore mother cell undergoes one meiotic division to produce four megaspores, but in a typical development like the Polygonum type found in maize, only one of these four megaspores remains functional, while the other three degenerate. The single functional megaspore then undergoes mitotic divisions to form the embryo sac containing the egg cell (ovule). Consequently, one meiotic division yields only one functional ovule (and thus one grain). To produce 100 ovules, 100 meiotic divisions are required. The total minimum number of meiotic divisions is the sum of male meiosis and female meiosis: $25 + 100 = 125$.

The incorrect option is 1: 100

This option incorrectly accounts for only one critical part of the reproductive process. A calculation of 100 meiotic divisions is sufficient only to produce the 100 female gametes (ovules, which become grains). It fails to include the minimum number of meiotic divisions—25 in this case—that are necessary to generate the 100 male gametes (pollen) required to fertilize those 100 ovules. Since both male and female meiosis contribute to the total, and the male meiosis is more efficient (4 pollen per meiosis), ignoring the male side leads to an incomplete and underestimated answer. This value represents only the meiotic divisions of the megaspore mother cells and is therefore too low to produce 100 viable grains.

The incorrect option is 2: 200

This number would incorrectly assume an inefficient gamete formation process for one or both sexes. For the female gametes, only 100 meiotic divisions are needed (1 meiotic division per ovule). For the male gametes, one meiotic division produces four pollen grains, requiring only 25 divisions for 100 pollen grains. The value of 200 suggests that one might have incorrectly assumed 100 female meiosis plus 100 male meiosis (1 male meiotic division yielding only 1 pollen grain), which contradicts the fundamental biological principle that male meiosis yields four functional spores. This overestimation is a classic conceptual error resulting from misapplying the meiotic efficiency.

The incorrect option is 3: 50

This option is significantly too low and would suggest a severe misunderstanding of the actual yield from meiotic divisions in angiosperms. The correct process demands 100 meiotic divisions just for the female gametes alone, as each ovule requires one distinct meiotic event. The value of 50 is lower than the required number of divisions for the female side, let alone the male side. It might be derived from an erroneous assumption, such as thinking that one meiotic division produces two grains, or by dividing the total required number of grains by an arbitrary factor. Therefore, 50 divisions would only produce 50 ovules, making the formation of 100 grains biologically impossible under these minimum conditions.