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Hatching rates for North American salamander species have ranged from 19.5% [10] to 30.5%. [11] It is speculated that intergenomic exchanges, like crossing over during meiosis , may play a role. Intergenomic exchanges are often lethal due to the fact that chromosomes in unisexual species are homeologous (similar, but less so than homologous ...
[9] [10] [11] This type of reproduction has been induced artificially in a number of animal species that naturally reproduce through sex, including fish, amphibians, and mice. [ 12 ] [ 13 ] Some species reproduce exclusively by parthenogenesis (such as the bdelloid rotifers ), while others can switch between sexual reproduction and parthenogenesis.
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. The fertilized egg cell is known as the zygote. [2] [5]
After internal fertilization and the habit of laying eggs in terrestrial environments became a reproduction strategy amongst the amniote ancestors, the next major breakthrough appears to have involved a gradual replacement of the gelatinous coating covering the amphibian egg with a fibrous shell membrane. This allowed the egg to increase both ...
Parthenogenesis is a mode of asexual reproduction in which offspring are produced by females without the genetic contribution of a male. Among all the sexual vertebrates, the only examples of true parthenogenesis, in which all-female populations reproduce without the involvement of males, are found in squamate reptiles (snakes and lizards). [1]
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 ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), the schistosome family of flatworms, and some reptiles, e.g. majority of snakes, lacertid lizards and monitors, including Komodo dragons.
The extraembryonic membranes are four membranes which assist in the development of an animal's embryo.Such membranes occur in a range of animals from humans to insects.They originate from the zygote, but are not considered part of the embryo.