A form of polyploidy that results from the multiplication of chromosome sets from a single species. Autopolyploids may arise either through a failure in the mitotic process (see syndiploidy), or in the meiotic process, resulting in the formation of diploid rather than haploid gametes. Autopolyploids often resemble their diploid parents, except that they may grow more slowly and flower later. Their cells are usually larger and the epidermis thicker. Autopolyploids with an uneven number of chromosome sets (autotriploids, autopentaploids) are often sterile because their gametes contain unbalanced numbers of chromosomes. Autotetra-ploids also show reduced fertility, the degree depending on whether any trivalents or univalents are formed at meiosis and also on the orientations taken up by the multivalents at meta-nhase. The patterns of inheritance, although they follow Mendelian laws, are very complex in autopolyploids because of the increased number of genotypes that may exist for any given locus with two alternative alleles. Thus for the two alleles A and a, a diploid can have three possible genotypes, AA, Aa, and aa, while an autotetraploid can have five, AAAA, AAAa, AAaa, Aaaa, and aaaa. In addition, while the frequencies of the gametes A and a can usually be predicted in diploids, the frequencies of the gametes AA, Aa, and aa of an autotetraploid are hard to predict because segregation can occur at either the first or second meiotic division. Compare allopolyploidy. |
