从我们认识到的“蕨类植物”(孢子体)开始,生命周期遵循以下步骤:二倍体孢子体通过减数分裂产生单倍体孢子,该过程在动物和开花植物中产生卵子和精子。每个孢子通过有丝分裂生长成光合原叶体(配子体)。由于有丝分裂维持染色体的数量,原叶中的每个细胞都是单倍体。这种苗比孢子体蕨小得多。每个原hall通过有丝分裂产生配子。减数分裂不需要,因为细胞已经是单倍体。通常,原叶体在同一植株上产生精子和卵子。虽然孢子体由叶状体和根状茎组成,但配子体具有小叶和根状茎。在配子体内,精子在一个叫做天蛾的结构内产生。这种鸡蛋是在一种类似的结构中产生的,称为一种颈椎。当水存在时,精子利用鞭毛游向卵子并使其受精。受精卵仍然附着于原叶。卵子是由卵子和精子DNA合成而成的二倍体合子。合子通过有丝分裂进入二倍体孢子体,完成生命周期。在科学家了解遗传学之前,蕨类植物的繁殖是神秘的。它看起来好像成年蕨类从孢子出现。从某种意义上说,这是事实,但从孢子中出现的小苗与成年蕨在遗传上是不同的。请注意,精子和卵子可能在同一配子体上产生,所以蕨类可能会自我施肥。自我受精的优势在于浪费的孢子更少,不需要外部配子载体,适合其环境的生物体可以保持其特征。交叉受精的优势在于它可能会引入新的特征。

新西兰奥克兰大学植物学代写:蕨类植物周期

Starting with the “fern” as we recognize it (the sporophyte), the life cycle follows these steps:The diploid sporophyte produces haploid spores by meiosis, the same process that produces eggs and sperm in animals and flowering plants.Each spore grows into a photosynthetic prothallus (gametophyte) via mitosis. Because mitosis maintains the number of chromosomes, each cell in the prothallus is haploid. This plantlet is much smaller than sporophyte fern.Each prothallus produces gametes via mitosis. Meiosis is not needed because the cells are already haploid. Often, a prothallus produces both sperm and eggs on the same plantlet. While the sporophyte consisted of fronds and rhizomes, the gametophyte has leaflets and rhizoids. Within the gametophyte, sperm is produced within a structure called an antheridium. The egg is produced within a similar structure called an archegonium.When water is present, sperm use their flagella to swim to an egg and ​fertilize it.The fertilized egg remains attached to the prothallus. The egg is a diploid zygote formed by the combination of DNA from the egg and sperm. The zygote grows via mitosis into the diploid sporophyte, completing the life cycle.Before scientists understood genetics, fern reproduction was mystifying. It appeared as though adult ferns arose from spores. In a sense, this is true, but the tiny plantlets that emerge from spores are genetically different from adult ferns.Note that sperm and egg may be produced on the same gametophyte, so a fern may self-fertilize. Advantages of self-fertilization are that fewer spores are wasted, no external gamete carrier is required, and organisms adapted to their environment can maintain their traits. The advantage of cross-fertilization, when it occurs, is that new traits may be introduced into the species.

发表评论

电子邮件地址不会被公开。 必填项已用*标注