Contrast the fertility of an allotetraploid with an autotriploid and an autotetraploid.

First, let's define the three types of plants we're dealing with: 1. Allotetraploid: A plant that has four sets (tetraploid) of chromosomes, two from each parent species. It results from hybridization between two different species. 2. Autotriploid: A plant that has three sets (triploid) of chromosomes, all from the same species. It occurs due to a spontaneous chromosomal duplication during cell division in the parent plant. 3. Autotetraploid: A plant that has four sets (tetraploid) of chromosomes, all from the same species. It also occurs due to a spontaneous chromosomal duplication during cell division in the parent plant.

During meiosis, homologous chromosomes must pair to form bivalents. Successful pairing of chromosomes is essential for the correct segregation of genetic material into gametes and the subsequent fertility of the organism: 1. In an allotetraploid, homologous chromosomes from different species can pair and form bivalents correctly because there are 4 sets of chromosomes, with each set having a complementary pair from the other parent species. This allows for regular meiosis and normal gamete formation, resulting in high fertility. 2. In an autotriploid, the plant has three homologous chromosomes, which complicates pairing during meiosis. Either two chromosomes pair and leave the third unpaired (resulting in unbalanced gametes, leading to aborted or nonviable offspring), or three homologous chromosomes try to form a trivalent (which often leads to misaligned chromosomes and chaotic segregation of genetic material during meiosis). Consequently, autotriploids face significant fertility issues. 3. In an autotetraploid, the presence of four homologous chromosomes allows them to pair up during meiosis. However, the pairing is not as simple as that of an allotetraploid sometimes, resulting in quadrivalents (when all four homologous chromosomes pair together) or other irregularities. Although autotetraploids typically have higher fertility rates than autotriploids due to regular meiosis, their fertility rates may still be lower than allotetraploids because of abnormalities that can occur in the paired chromosomes.

Now that we've outlined how chromosome pairing during meiosis affects the fertility of each type of plant, we can compare and contrast: 1. Allotetraploids exhibit high fertility rates because their hybrid nature allows for proper chromosome pairing during meiosis and normal gamete formation. 2. Autotriploids face significant fertility issues due to having an odd number of chromosome sets, causing complications in pairing during meiosis, leading to nonviable or aborted offspring. 3. Autotetraploids generally have higher fertility rates than autotriploids because they have four homologous chromosomes that allow pairing during meiosis. However, their fertility rates may still be lower than allotetraploids because irregularities in chromosome pairing can lead to abnormalities during meiosis. In conclusion, the fertility of these plants can be ranked as follows: allotetraploids have the highest fertility, autotetraploids have intermediate fertility (although somewhat lower than allotetraploids), and autotriploids have the lowest fertility among the three types.