double fertilization

Examples of double fertilization in the following topics:

• Double Fertilization in Plants

  • Angiosperms undergo two fertilization events where a zygote and endosperm are both formed.
  • Together, these two fertilization events in angiosperms are known as double fertilization .
  • After fertilization is complete, no other sperm can enter.
  • After fertilization, embryonic development begins.
  • This is called a double fertilization.

• The Life Cycle of an Angiosperm

  • Angiosperms are seed-producing plants that generate male and female gametophytes, which allow them to carry out double fertilization.
  • A double fertilization event then occurs.
  • After fertilization and some growth in the angiosperm, the ripened ovule is produced.
  • Double fertilization is a process unique to angiosperms.

• Development of the Seed

  • In angiosperms, the process of seed development begins with double fertilization and involves the fusion of the egg and sperm nuclei into a zygote.
  • In gymnosperms, the two sperm cells transferred from the pollen do not develop seed by double fertilization, but one sperm nucleus unites with the egg nucleus and the other sperm is not used.
  • Sometimes each sperm fertilizes an egg cell and one zygote is then aborted or absorbed during early development.
  • The ovules after fertilization develop into the seeds.
  • In non-endospermic dicots, the triploid endosperm develops normally following double fertilization, but the endosperm food reserves are quickly remobilized, moving into the developing cotyledon for storage.

• Sexual Reproduction in Gymnosperms

  • After fertilization of the egg, the diploid zygote is formed, which divides by mitosis to form the embryo.
  • Double fertilization is a key event in the life cycle of angiosperms, but is completely absent in gymnosperms.
  • Pollen from male cones blows up into upper branches, where it fertilizes female cones.

• Introduction to Meiosis

  • Sexual reproduction requires fertilization: the union of two cells from two individual organisms.
  • If the reproductive cycle is to continue, then the diploid cell must somehow reduce its number of chromosome sets before fertilization can occur again or there will be a continual doubling in the number of chromosome sets in every generation.
  • Sexual reproduction is the production of haploid cells (gametes) and the fusion (fertilization) of two gametes to form a single, unique diploid cell called a zygote.

• Sexual Reproduction in Angiosperms

  • Once fertilization is complete, the resulting diploid zygote develops into the embryo; the fertilized ovule forms the other tissues of the seed.
  • A double-layered integument protects the megasporangium and, later, the embryo sac.
  • The integument will develop into the seed coat after fertilization, protecting the entire seed.
  • The micropyle allows the pollen tube to enter the female gametophyte for fertilization.
  • The corn kernels are seeds that develop on the ear after fertilization.

• External and Internal Fertilization

  • After the sperm reaches the egg, fertilization can then take place.
  • External fertilization in an aquatic environment protects the eggs from drying out.
  • Internal fertilization has the advantage of protecting the fertilized egg from dehydration on land.
  • Internal fertilization also enhances the fertilization of eggs by a specific male.
  • The anemone fish utilizes a form of external fertilization.

• Fertilization

  • In fertilization, the sperm binds to the egg, allowing their membranes to fuse and the sperm to transfer its nucleus into the egg.
  • Fertilization is the process in which gametes (an egg and sperm) fuse to form a zygote.
  • The egg and sperm are haploid, which means they each contain one set of chromosomes; upon fertilization, they will combine their genetic material to form a zygote that is diploid, having two sets of chromosomes.
  • To ensure that no more than one sperm fertilizes the egg, once the acrosomal reactions take place at one location of the egg membrane, the egg releases proteins in other locations to prevent other sperm from fusing with the egg.
  • (a) Fertilization is the process in which sperm and egg fuse to form a zygote.

• Ferns and Other Seedless Vascular Plants

  • Water is required for fertilization of seedless vascular plants; most favor a moist environment.
  • Fronds fulfill a double role; they are photosynthetic organs that also carry reproductive organs.
  • Flagellated sperm are released and swim on a wet surface to where the egg is fertilized.

• Endosymbiotic Theory and the Evolution of Eukaryotes

  • The mitochondrial DNA degrades in sperm when the sperm degrades in the fertilized egg or, in other instances, when the mitochondria located in the flagellum of the sperm fails to enter the egg.
  • The double membrane would be a direct result of endosymbiosis, with the endosymbiont picking up the second membrane from the host as it was internalized.
  • This mechanism has also been used to explain the double membranes found in mitochondria and chloroplasts.