Parts Corn Plant

eios

Meiosis

Zygote

Zygote

Many mitoses

Many mitoses

2n Adult

2n Adult

Stage The Life Cycle Egg Zygote Sperm

Figure 3-33 The alternation of diploid and haploid stages in the life cycle of plants.

Figure 3-31 The diploid life cycle.

Figure 3-33 The alternation of diploid and haploid stages in the life cycle of plants.

all, meiosis requires the pairing of two homologous chromosome sets. The answer is that two haploid cells of two parental strains fuse to form a temporary diploid meiocyte. Meiosis takes place in the meiocyte, forming haploid spores. Organisms with alternating haploid-diploid generations: organisms that are haploid for part of the life cycle and diploid for part of the life cycle. Both haploid and diploid parts grow by mitosis, but meiosis occurs only in the diploid stage. Plants show such alternation of haploid and diploid generations: the organism during the haploid stage of the cycle is called the gametophyte and during the diploid part the sporophyte, as shown in Figure 3-33. Plants such

Parts Gametophyte

Figure 3-34 Alternation of generations of corn. The male gametophyte arises from a meiocyte in the tassel. The female gametophyte arises from a meiocyte in the ear shoot. One sperm cell from the male gametophyte fuses with an egg nucleus of the female gametophyte, and the diploid zygote thus formed develops into the embryo. The other sperm cell fuses with the two polar nuclei in the center of the female gametophyte, forming a triploid (3n) cell that generates the endosperm tissue surrounding the embryo. The endosperm provides nutrition to the embryo during seed germination. Which parts of the diagram represent the haploid stage? Which parts represent the diploid stage?

Figure 3-34 Alternation of generations of corn. The male gametophyte arises from a meiocyte in the tassel. The female gametophyte arises from a meiocyte in the ear shoot. One sperm cell from the male gametophyte fuses with an egg nucleus of the female gametophyte, and the diploid zygote thus formed develops into the embryo. The other sperm cell fuses with the two polar nuclei in the center of the female gametophyte, forming a triploid (3n) cell that generates the endosperm tissue surrounding the embryo. The endosperm provides nutrition to the embryo during seed germination. Which parts of the diagram represent the haploid stage? Which parts represent the diploid stage?

as ferns and mosses have separate free-living haploid and diploid stages. Flowering plants are predominantly diploid but do have a small haploid gameto-phytic stage parasitic on the diploid within the flower (see Figure 3-34, which shows the corn life cycle). However, for most genetic purposes plants can be treated simply as showing a diploid cycle.

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Responses

  • Paul
    What is an alternation of haploid and diploid phases?
    7 years ago
  • marcus
    Is the end of meiosis 1 diploid or haploid?
    7 years ago
  • Columbus
    How many cells are the female gametophyte of flowers?
    7 years ago
  • linda
    What are the steps of seed generation?
    7 years ago
  • nancy
    How a corn plant develops?
    6 years ago

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