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chapter48%20Animal%20Reproduction[1]

chapter48%20Animal%20Reproduction[1] - BLY 122 Chapter 48...

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BLY 122 A. Hunter from C. S. Major Chapter 48 Animal Reproduction I. Asexual and Sexual Reproduction A. The offspring of asexual reproduction are genetically identical to their parent; asexual reproduction occurs in a variety of ways. 1. Budding is when offspring forms on or in a parent and eventually breaks free. 2. A new individual forms from a fragment of another in regeneration. 3. Fission is the process by which two new individuals are formed when an animal splits apart. 4. Parthenogenesis is the production of offspring from unfertilized eggs. a. Many species reproduce via parthogenesis. b. These include fish, rotifers, and insects. B. Daphnia switch to sexual reproduction when environmental cues indicate that conditions are becoming adverse. 1. Daphnia are crustaceans that live in freshwater habitats. 2. They reproduce asexually, but produce only diploid females in the spring and summer via parthogenesis. 3. In late summer, diploid females produce males via parthogenesis. 4. This is when sexual reproduction begins. 5. Why does this switch occur? a. Researchers found a strong correlation between population density and the number of females reproducing sexually. b. Further studies showed high population density, low food availability, and short day length were all needed for the switch to occur. c. This likely happens because offspring produced by sexual reproduction have greater genetic diversity and more fitness to survive in a resource-limited environment. C. Mechanisms of Sexual Reproduction: Gametogenesis 1. Gametogenesis is the formation of gametes, better known as egg and sperm. a. Spermatogenesis takes place in the male gonads, the testes. b. Oogenesis takes place in the female gonads, the ovaries. 2. Gametogenesis is very different in males and females. a. In males, a diploid spermatogonia divides via mitosis to generate primary spermatocytes. b. In females, a diploid oogonium divides mitotically to generate a primary oocyte. c. Egg cells are much larger than sperm cells due to the unequal distribution of cytoplasm during meiotic divisions. II. Fertilization and Egg Development A. Fertilization can occur externally in the environment or internally in the female reproductive tract. 1. Species that use external fertilization produce large numbers of gametes and require cues to synchronize the release of sperm and eggs. 2. Internal fertilization involves the male directly depositing sperm into the female reproductive tract. a. This act, called copulation, is often enabled by the male organ, the penis.
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