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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]
Some females abort or resorb their own young while they are still in development after a new male takes over; this is known as the Bruce effect. [31] This may prevent their young from being killed after birth, saving the mother wasted time and energy. However, this strategy also benefits the new male.
In animals, fertilization begins the process of embryonic development with the creation of a zygote, a single cell resulting from the fusion of gametes (e.g. egg and sperm). [5] The development of a zygote into a multicellular embryo proceeds through a series of recognizable stages, often divided into cleavage, blastula, gastrulation, and ...
Human babies are unique in the animal kingdom due to their large head size relative to their bodies. This has an effect on the birthing process for humans as the bipedal gait of a human causes the birthing canal to be relatively narrow and twisted in the middle.
Animals have life cycles with a single diploid multicellular phase that produces haploid gametes directly by meiosis. Male gametes are called sperm, and female gametes are called eggs or ova. In animals, fertilization of the ovum by a sperm results in the formation of a diploid zygote that develops by repeated mitotic divisions into a diploid ...
Parthenogenesis is the growth and development of embryo or seed without fertilization. Parthenogenesis occurs naturally in some species, including lower plants (where it is called apomixis ), invertebrates (e.g. water fleas , aphids , some bees and parasitic wasps ), and vertebrates (e.g. some reptiles, [ 3 ] some fish, [ 4 ] and very rarely ...
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The development of the reproductive system is the part of embryonic growth that results in the sex organs and contributes to sexual differentiation. Due to its large overlap with development of the urinary system , the two systems are typically described together as the genitourinary system .