Reproduction and Embryonic Development Chapter 27 Sec 1-2 Reproduction and Embryonic Development

Introduction Fertility drugs Fertility drugs increase the number of eggs that are ovulated and have allowed thousands of infertile couples to have babies. Ten percent of women taking fertility drugs become pregnant with more than one embryo. © 2012 Pearson Education, Inc. 2

Introduction Newborns from multiple births are Newborns from multiple births are more likely to be premature, more likely to have lower birth weights, and less likely to survive. © 2012 Pearson Education, Inc. 3

Asexual and Sexual Reproduction Principles of Embryonic Development Figure 27.0_1 Chapter 27: Big Ideas Asexual and Sexual Reproduction Human Reproduction Figure 27.0_1 Chapter 27: Big Ideas Principles of Embryonic Development Human Development 4

Figure 27.0_2 Figure 27.0_2 The rate of twin births has increased due to the use of fertility drugs. 5

ASEXUAL AND SEXUAL REPRODUCTION ASEXUAL AND SEXUAL REPRODUCTION © 2012 Pearson Education, Inc. 6

27.1 Asexual reproduction results in the generation of genetically identical offspring Asexual reproduction is the creation of genetically identical offspring by one parent, is a very rapid form of reproduction, and can proceed via budding, fission, or fragmentation/regeneration. Student Misconceptions and Concerns Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. © 2012 Pearson Education, Inc. 7

Video: Hydra Budding Student Misconceptions and Concerns Student Misconceptions and Concerns Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. Teaching Tips Aphid life cycles usually alternate between asexual and sexual reproductive strategies during a single year. Consider challenging your class to explain why aphids (and other animals) do this. In general, sexual reproduction is most common in times of stress, and may be related to overpopulation or environmental change in which diversity may be favored. Video: Hydra Budding Use window controls to play © 2012 Pearson Education, Inc. 8

Figure 27.1A Figure 27.1A Asexual reproduction via budding in a hydra 9

Figure 27.1B Figure 27.1B Asexual reproduction of a sea anemone (Anthopleura elegantissima) by fission 10

27.2 Sexual reproduction results in the generation of genetically unique offspring Sexual reproduction is the creation of offspring by fertilization and joins two haploid sex cells or gametes to form a diploid (2n) zygote. Student Misconceptions and Concerns 1. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. 2. Many students expect that hermaphroditic animals simply fertilize themselves. Although this may be common in some animals, the exchange of gametes between hermaphrodites also occurs, as noted in the text. Teaching Tips Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base attached to the substrate. The female moves over the spermatophore, removes some or all of the sperm from the cap, and stores the sperm in her reproductive tract (a spermatheca) until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. © 2012 Pearson Education, Inc. 11

27.2 Sexual reproduction results in the generation of genetically unique offspring The male gamete, the sperm, is relatively small and moves by means of a flagellum. The female gamete, the egg, is a much larger cell and is not self-propelled. Student Misconceptions and Concerns 1. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. 2. Many students expect that hermaphroditic animals simply fertilize themselves. Although this may be common in some animals, the exchange of gametes between hermaphrodites also occurs, as noted in the text. Teaching Tips 1. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base attached to the substrate. The female moves over the spermatophore, removes some or all of the sperm from the cap, and stores the sperm in her reproductive tract (a spermatheca) until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. © 2012 Pearson Education, Inc. 12

27.2 Sexual reproduction results in the generation of genetically unique offspring Some organisms, such as sea anemones, can reproduce both asexually and sexually. Student Misconceptions and Concerns 1. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. 2. Many students expect that hermaphroditic animals simply fertilize themselves. Although this may be common in some animals, the exchange of gametes between hermaphrodites also occurs, as noted in the text. Teaching Tips 1. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base attached to the substrate. The female moves over the spermatophore, removes some or all of the sperm from the cap, and stores the sperm in her reproductive tract (a spermatheca) until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. © 2012 Pearson Education, Inc. 13

Video: Hydra Releasing Sperm Student Misconceptions and Concerns 1. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. 2. Many students expect that hermaphroditic animals simply fertilize themselves. Although this may be common in some animals, the exchange of gametes between hermaphrodites also occurs, as noted in the text. Teaching Tips 1. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base attached to the substrate. The female moves over the spermatophore, removes some or all of the sperm from the cap, and stores the sperm in her reproductive tract (a spermatheca) until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. Video: Hydra Releasing Sperm Use window controls to play © 2012 Pearson Education, Inc. 14

Two offspring arising by fission Figure 27.2A Eggs Two offspring arising by fission Figure 27.2A Asexual (left) and sexual (right) reproduction in the starlet sea anemone (Nematostella vectensis) 15

27.2 Sexual reproduction results in the generation of genetically unique offspring Some animals exhibit hermaphroditism in which an individual has both female and male reproductive systems. Hermaphroditism makes it easier to find a mate for animals that are solitary or less mobile. Hermaphrodites may exchange gametes with other individuals or fertilize their own eggs. Student Misconceptions and Concerns 1. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. 2. Many students expect that hermaphroditic animals simply fertilize themselves. Although this may be common in some animals, the exchange of gametes between hermaphrodites also occurs, as noted in the text. Teaching Tips 1. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base attached to the substrate. The female moves over the spermatophore, removes some or all of the sperm from the cap, and stores the sperm in her reproductive tract (a spermatheca) until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. © 2012 Pearson Education, Inc. 16

Figure 27.2B Figure 27.2B Hermaphroditic earthworms mating 17

27.2 Sexual reproduction results in the generation of genetically unique offspring External fertilization occurs when eggs and sperm are discharged near each other and is used by many fish and amphibian species. Internal fertilization occurs when sperm is deposited in or near the female reproductive tract and is used by some fish and amphibian species and nearly all terrestrial animals. Student Misconceptions and Concerns 1. Students do not often understand the costs and benefits of asexual and sexual reproduction. Consider discussing the advantages and disadvantages of each of these forms of reproduction. Encourage students to focus on the compromises involved in any adaptation. There is simply no one “best” way for all animals to reproduce. 2. Many students expect that hermaphroditic animals simply fertilize themselves. Although this may be common in some animals, the exchange of gametes between hermaphrodites also occurs, as noted in the text. Teaching Tips 1. Many salamander species use spermatophores to transfer sperm from the male to the female. Spermatophores are reproductive structures produced by males during courtship. Sperm is deposited atop a gelatinous base attached to the substrate. The female moves over the spermatophore, removes some or all of the sperm from the cap, and stores the sperm in her reproductive tract (a spermatheca) until the time of egg deposition. Thus, sperm transfer is external but fertilization is internal. © 2012 Pearson Education, Inc. 18

Figure 27.2C Figure 27.2C Frogs in an embrace that triggers the release of eggs and sperm (the sperm are too small to be seen) Egg 19