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

2. 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.
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3. 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.
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4. 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

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

6. ASEXUAL AND SEXUAL REPRODUCTION
ASEXUAL AND SEXUAL REPRODUCTION
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7. 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.
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8. 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
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9. Figure 27.1A
Figure 27.1A Asexual reproduction via budding in a hydra 9

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

11. 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.
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12. 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.
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13. 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.
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14. 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
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15. 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

16. 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.
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17. Figure 27.2B
Figure 27.2B Hermaphroditic earthworms mating 17

18. 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.
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19. 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