Bisporic embryo sacs contain nuclei derived from two members of a megaspore tetrad whereas tetrasporic embryo sacs contain nuclei derived from all four members of a tetrad. Megaspores from the same tetrad are less genetically similar than are megaspores from different tetrads. Therefore, cells derived from different megaspores in bisporic and tetrasporic embryo sacs are expected to compete with each other rather than cooperate. The tacit assumption of the plant embryological literature that bisporic and tetrasporic embryo sacs function as integrated organisms is demonstrably false, both theoretically and empirically. This competition within embryo sacs can be expressed as the formation of eggs by descendants of more than one megaspore or by the suppression of the descendants of all but one megaspore. Both phenomena have evolved multiple times. In contrast, all nuclei of monosporic female gametophytes are genetically identical. Consequently, monosporic development is predicted to be more evolutionarily stable than bisporic or tetrasporic development. The triploid endosperm produced by most monosporic gametophytes was probably derived from an ancestrally diploid endosperm and has been considered a key adaptation of the most successful lineages of flowering plants. The greater weight given to the doubled maternal genome in triploid endosperm may have facilitated a more efficient distribution of resources among a mother’s seeds because it reduced the influence of competition for maternal resources among unrelated paternal genomes of endosperm.

中文翻译：

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两极分化：重新审视单孢子、双孢子和四孢子胚囊

双孢子胚囊包含源自大孢子四分体的两个成员的细胞核，而四孢子胚囊包含源自四分体所有四个成员的细胞核。与来自不同四分体的大孢子相比，来自同一四分体的大孢子在遗传上不太相似。因此，来自双孢子和四孢子胚囊中不同大孢子的细胞有望相互竞争而不是合作。植物胚胎学文献中关于双孢子和四孢子胚囊作为整合生物发挥作用的默认假设在理论上和经验上都是错误的。胚囊内的这种竞争可以表现为多个大孢子的后代形成卵或抑制除一个大孢子外的所有后代的后代。这两种现象都经历了多次演变。相比之下，单孢雌配子体的所有细胞核在遗传上都是相同的。因此，预计单孢子发育比双孢子或四孢子发育在进化上更稳定。大多数单孢子配子体产生的三倍体胚乳可能来自祖先的二倍体胚乳，并被认为是最成功的开花植物谱系的关键适应性。三倍体胚乳中双倍母本基因组的更大权重可能有助于更有效地在母本种子之间分配资源，因为它减少了不相关的胚乳父本基因组之间对母本资源竞争的影响。预计单孢子发育比双孢子或四孢子发育更稳定。大多数单孢子配子体产生的三倍体胚乳可能来自祖先的二倍体胚乳，并被认为是最成功的开花植物谱系的关键适应性。三倍体胚乳中双倍母本基因组的更大权重可能有助于更有效地在母本种子之间分配资源，因为它减少了不相关的胚乳父本基因组之间对母本资源竞争的影响。预计单孢子发育比双孢子或四孢子发育更稳定。大多数单孢子配子体产生的三倍体胚乳可能来自祖先的二倍体胚乳，并被认为是最成功的开花植物谱系的关键适应性。三倍体胚乳中双倍母本基因组的更大权重可能有助于更有效地在母本种子之间分配资源，因为它减少了不相关的胚乳父本基因组之间对母本资源竞争的影响。大多数单孢子配子体产生的三倍体胚乳可能来自祖先的二倍体胚乳，并被认为是最成功的开花植物谱系的关键适应性。三倍体胚乳中双倍母本基因组的更大权重可能有助于更有效地在母本种子之间分配资源，因为它减少了不相关的胚乳父本基因组之间对母本资源竞争的影响。大多数单孢子配子体产生的三倍体胚乳可能来自祖先的二倍体胚乳，并被认为是最成功的开花植物谱系的关键适应性。三倍体胚乳中双倍母本基因组的更大权重可能有助于更有效地在母本种子之间分配资源，因为它减少了不相关的胚乳父本基因组之间对母本资源竞争的影响。