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External fertilization is a mode of reproduction in which a male organism's sperm fertilizes a female organism's egg outside of the female's body. [1] It is contrasted with internal fertilization , in which sperm are introduced via insemination and then combine with an egg inside the body of a female organism.
The biologist Thierry Lodé proposed (2001, 2012) five modes of reproduction based on the relationship between the zygote (fertilised egg) and the parents: [1] [2] Ovuliparity: fertilisation is external, the oocytes being released into the environment and fertilised outside the body by the male. [1]
Human reproduction usually involves internal fertilization by sexual intercourse. In this process, the male inserts his penis into the female's vagina and ejaculates semen, which contains sperm. A small proportion of the sperm pass through the cervix into the uterus and then into the fallopian tubes for fertilization of the ovum. Only one sperm ...
Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization , brings more control to the female with reproduction. [ 1 ]
(True) oviparity, in which fertilization is internal, is taken to be the derived condition, whether the male injects the sperm into the female intromittently or whether she actively or passively picks it up — the female lays eggs containing zygotes with a substantial quantity of yolk to feed the embryo while it remains in the egg, and in many ...
Fertilization is the fusion of gametes to produce a new organism. In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external fertilization.
Internal self-fertilization may occur in some other species. [44] One fish species does not reproduce by sexual reproduction but uses sex to produce offspring; Poecilia formosa is a unisex species that uses a form of parthenogenesis called gynogenesis , where unfertilized eggs develop into embryos that produce female offspring.
Offspring inherit one allele for each trait from each parent. Thus, offspring have a combination of the parents' genes. It is believed that "the masking of deleterious alleles favors the evolution of a dominant diploid phase in organisms that alternate between haploid and diploid phases" where recombination occurs freely. [12] [13]