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Animal Reproduction

Animal Reproduction - Animal Reproduction Both asexual and...

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Animal Reproduction Both asexual and sexual reproduction occur in the animal kingdom o In sexual reproduction, 2 meiotically formed haploid gametes fuse to form a diploid zygote, which develops into an offspring. o Games are usually relatively large, nonmotile egg, and a small, motile sperm. o In asexual reproduction, a single individual produces offspring, usually using only mitotic cell division. o Mechanisms of Asexual Reproduction Many invertebrates can reproduce asexually by fission, in which a parent is separated into 2 or more individuals of equal size Or by budding, in which a new individual grows out from the parent’s body Or by fragmentation, in which the body is broken into several pieces, each of which develops into a complete animal. Regeneration is the regrowth of body parts, and is necessary for a fragment to develop into a new organism. In parthenogenesis, eggs develop without being fertilized o Sexual Reproduction: An Evolutionary Enigma Asexual reproduction potentially produces many more offspring, yet most eukaryotic species reproduce sexually. The shuffling of genes in sexual reproduction may allow more rapid adaptation to changing conditions or allow harmful genes to be eliminated more easily. o Reproductive Cycles and Patterns Periodic reproductive cycles may be linked to favorable conditions or energy supplies. Ovulation is controlled by a combination of environmental and hormonal cues. Animals may reproduce sexually, asexually, or both. Freshwater crustacean Daphnia, like aphids and rotifers, produces eggs that develop by parthenogenesis, as well as eggs that are fertilized. Parthenogensis works in that chromosomes double after meiosis, creating diploid offspring. In hermaphroditism, each individual has functioning male and female reproductive systems. Mating results in fertilization of both individuals. Fertilization depends on mechanisms that bring together sperm and eggs of the same species o Fertilization is the union of sperm and egg o In External Fertilization, eggs and sperm are shed, and fertilization occurs in the environment.
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External fertilization occurs almost exclusively in moist habitats, where gametes and developing zygote are not in danger of desiccation. o Internal fertilization involves the placement of sperm in or near the female reproductive trac so that the egg and sperm unite internally. Behavioral cooperation, as well as copulatory organs and sperm receptacles, are required for internal fertilization. o Pheromones are small, volatile chemical signals that may function as mate attractants. o Ensuring the Survival of Offspring Species with external fertilization usually produce huge numbers of gametes; only a fraction of zygotes survive.
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