Maletskiĭ S I, Shkutnik T, Prusinskaia E, Chervchak U
Institute of Cytology and Genetics, Russian Academy of Sciences, Novosibirsk, 630090 Russia.
Genetika. 2001 Mar;37(3):344-9.
Expression of Mdh1 alleles has been studied in 60 apozygotic (agamospermic) sugar beet progenies. Seed progenies were obtained by uniparental (pollen less) mode of seed reproduction: selfing of pollen-sterile plants isolated with paper bags. The apozygotic seed progenies demonstrate a disomic gamete autosegregation, i.e., the ratio between genotypes in the progenies correspond to the gamete segregation in a duplex heterozygote of an autotetraploid. It was shown that the ratio between the Mdh1 phenotypes in apozygotic progenies is strongly affected by spontaneous inactivation of one of the alleles. In most progenies, the excess of FF phenotypes and the deficit of SS phenotypes were observed. In our opinion, such deviations in genotype and phenotype frequencies result from conversion of the active Mdh1-S into the inactive Mdh1-S0 allele (epigenetic gene inactivation). The spontaneous inactivation of one allele results in extremely variable frequencies of heterozygous Mdh1-F/Mdh1-S genotypes and phenotypes in the apozygotic seed progenies. The empirical distribution of the frequencies of heterozygous genotypes in the apozygotic seed progenies is given by a negative binomial distribution describing the expected time of occurrence of random events.
已在60个无融合生殖（无配子生殖）的甜菜后代中研究了Mdh1等位基因的表达。种子后代通过单亲（无花粉）种子繁殖方式获得：用纸袋隔离的花粉不育植物进行自交。无融合生殖的种子后代表现出二体配子自分离，即后代中基因型之间的比例与同源四倍体双杂合子中的配子分离相对应。结果表明，无融合生殖后代中Mdh1表型之间的比例受到其中一个等位基因自发失活的强烈影响。在大多数后代中，观察到FF表型过多而SS表型不足。我们认为，基因型和表型频率的这种偏差是由于活性Mdh1-S转化为无活性的Mdh1-S0等位基因（表观遗传基因失活）所致。一个等位基因的自发失活导致无融合生殖种子后代中杂合Mdh1-F/Mdh1-S基因型和表型的频率极具变异性。无融合生殖种子后代中杂合基因型频率的经验分布由描述随机事件预期发生时间的负二项分布给出。
