TAILIEUCHUNG - Lecture Biology: Chapter 46 - Niel Campbell, Jane Reece

After studying this chapter you will be able to: Distinguish between asexual and sexual reproduction; explain how hermaphroditism may be advantageous to animals that have difficulty encountering a member of the opposite sex; describe various ways in which animals may protect developing embryos; using diagrams, identify and state the function of each component of the male and female reproductive systems;. | Chapter 46 Animal Reproduction Overview: Pairing Up for Sexual Reproduction Each earthworm produces sperm and eggs; in a few weeks, new worms will hatch from fertilized eggs. Animal reproduction takes many forms. Aspects of animal form and function can be viewed broadly as adaptations contributing to reproductive success. How can each of these earthworms be both male and female? Figure How can each of these earthworms be both male and female? Both asexual and sexual reproduction occur in the animal kingdom Sexual reproduction is the creation of an offspring by fusion of a male gamete (sperm) and female gamete (egg) to form a zygote. Asexual reproduction is creation of offspring without the fusion of egg and sperm . One parent clones offspring. Many invertebrates reproduce asexually by fission = separation of a parent into two or more individuals of about the same size. Asexual reproduction of a sea anemone Figure elegantissima) Budding = new individuals arise from outgrowths of existing ones. Fragmentation = breaking of the body into pieces, some or all of which develop into adults. Fragmentation must be accompanied by regeneration = regrowth of lost body parts. Parthenogenesis is the development of a new individual from an unfertilized egg. Asexual Reproduction Sexual Reproduction: An Evolutionary Enigma Sexual females have half as many daughters as asexual females; this is the “twofold cost” of sexual reproduction. Despite this, almost all eukaryotic species reproduce sexually. The “reproductive handicap” of sex: Sexual females have half as many daughters as asexual females. Asexual reproduction Female Sexual reproduction Female Generation 1 Male Generation 2 Generation 3 Generation 4 Figure Sexual reproduction results in genetic recombination, which provides potential advantages: An increase in variation in offspring, providing an increase in the reproductive success of parents in changing environments An increase in the rate

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