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  1. Splash

  2. Chapter Introduction Cell Division and Reproduction 12.1 Asexual Reproduction 12.2 Chromosome Numbers 12.3 Meiosis and the Production of Gametes Sexual Reproduction 12.4 Sexual Reproduction in Microorganisms 12.5 Sexual Reproduction in Plants 12.6 Sexual Reproduction in Animals Reproduction in Humans 12.7 Egg Production and the Menstrual Cycle 12.8 Sperm Production 12.9 Secondary Sex Characteristics 12.10 Infertility and Contraception Chapter Highlights Chapter Animations Chapter Menu Contents

  3. Learning Outcomes By the end of this chapter you will be able to: A Describe reproduction in plants and animals. B Explain the importance of meiosis in maintaining chromosome numbers and identify the stages of meiosis. C Infer the advantages of a dominant diploid stage in the life cycle of plants and animals. D Relate the process of fertilization in flowering plants to their successful domination of land environments. E Compare external and internal fertilization. F Discuss the influence of hormones on the human male and female reproductive systems. G Discuss causes of infertility and methods of contraception. Learning Outcomes

  4. This photo shows a bee visiting the disc florets of a flower in the Asteraceae family. Reproduction • What benefit does the flower gain from the activity of this bee? • How might a cluster of flowers give this species a reproductive advantage? Chapter Introduction 1

  5. This photo shows a bee visiting the disc florets of a flower in the Asteraceae family. Reproduction • For a species to survive, it must reproduce successfully in every generation. • Some organisms reproduce individually; their offspring are genetically identical to the parent. • Others reproduce sexually, producing offspring that receive genetic information from two parents. Chapter Introduction 2

  6. End of the Introduction

  7. Cell Division and Reproduction 12.1 Asexual Reproduction • Asexual reproduction requires a single parent where one or more of their cells form a genetically identical offspring. A group of genetically identical cells or organisms produced through asexual reproduction is called a clone. 12.1 Asexual Reproduction 1

  8. Cell Division and Reproduction 12.1 Asexual Reproduction (cont.) • Prokaryotes and one-celled eukaryotes reproduce by simply dividing in two, a process called binary fission. Other eukaryotic organisms that reproduce asexually include many fungi and simple animals. 12.1 Asexual Reproduction 2

  9. Mitotic cell division in Paramecium caudatum(color added, x400) Budding in Hydra viridis(color added, x8) fragmentation in Planaria Cell Division and Reproduction 12.1 Asexual Reproduction (cont.) 12.1 Asexual Reproduction 3

  10. Cell Division and Reproduction 12.1 Asexual Reproduction (cont.) • Some plants reproduce through fragmentation. Asexual reproduction in plants, or vegetative reproduction, is efficient in filling an area with plants, but it is less successful in quickly spreading plants to new locations. 12.1 Asexual Reproduction 4

  11. Fragments of the cactus known as jumping cholla (Opuntia bigelovii) break off easily and are carried by wind or animals to new locations. The fragments form new plants where they land. Leaves of Bryophyllum produce little plantlets, each of which may fall to the ground near the parent and grow as a new plant. Cell Division and Reproduction 12.1 Asexual Reproduction (cont.) 12.1 Asexual Reproduction 5

  12. Cell Division and Reproduction 12.2 Chromosome Numbers • Each species has a characteristic number of chromosomes. Prokaryotes generally have only one major chromosome, consisting of a single circle of DNA. The number of chromosomes varies among eukaryotes. 12.2 Chromosome Numbers 1

  13. Cell Division and Reproduction 12.2 Chromosome Numbers (cont.) • Cells of most organisms that reproduce sexually have pairs of similar chromosomes. • Each parent provides one member of each pair. Cells that carry a double set of chromosomes are called diploid (2n). Cells with just one set of chromosomes are called haploid (n). 12.2 Chromosome Numbers 2

  14. Changes in chromosome number in a typical sexual life cycle. 12.2 Chromosome Numbers 3

  15. Cell Division and Reproduction 12.2 Chromosome Numbers (cont.) • In diploid organisms, the two chromosomes of a pair are called homologous. Homologous chromosomes, or homologues, with the exception of the sex chromosomes, are similar in structure. Homologues carry the same genes, though differences in their DNA sequences produce the variety you see among members of the same species. 12.2 Chromosome Numbers 4

  16. Cell Division and Reproduction 12.2 Chromosome Numbers (cont.) • In asexual reproduction, the cells of parent and offspring carry identical sets of chromosomes. In sexual reproduction, the reproductive cells that fuse during sexual reproduction must each be haploid. If reproductive cells were diploid like somatic cells, the number of chromosomes would double in each generation. 12.2 Chromosome Numbers 5

  17. Cell Division and Reproduction 12.2 Chromosome Numbers (cont.) • In sexual reproduction, each parent produces haploid gametes. Male gametes are sperm, and female gametes are ova (singular: ovum), or eggs. During fertilization, male and female gametes join, and their nuclei fuse. A new individual develops from the diploid fertilized egg, or zygote. 12.2 Chromosome Numbers 6

  18. Cell Division and Reproduction 12.2 Chromosome Numbers (cont.) • A special cell-division process, meiosis, produces the haploid gametes that must generally either fuse with another gamete or die. In fungi and simple plants, meiosis produces different types of haploid cells called spores. Most spores can develop into haploid organisms without fertilization. 12.2 Chromosome Numbers 7

  19. Populations of desert whiptail lizards, Cnemidophorus neomexicanus, consist entirely of females. The factors that led to natural selection for asexual reproduction in these populations are not yet clear. Cell Division and Reproduction 12.2 Chromosome Numbers (cont.) • A few species of plants and animals have lost the ability to reproduce sexually. 12.2 Chromosome Numbers 8

  20. Cell Division and Reproduction 12.3 Meiosis and the Production of Gametes • Meiosis differs from mitosis in three important ways: 1. Cells divide twice during meiosis, but the chromosomes are not duplicated after the first division. 2. Meiosis distributes a random mixture of maternal and paternal chromosomes to each gamete resulting in new genetic combinations. 12.3 Meiosis and the Production of Gametes 1

  21. Cell Division and Reproduction 12.3 Meiosis and the Production of Gametes (cont.) 3. Homologous chromosomes pair up side by side during the first meiotic division, often exchanging corresponding pieces of DNA. • This exchange is called crossing-over. • Crossing-over changes each chromosome into a mixture of maternal and paternal genes adding to the genetic variety of the gametes. 12.3 Meiosis and the Production of Gametes 2

  22. Meiosis 12.3 Meiosis and the Production of Gametes 3

  23. Cell Division and Reproduction 12.3 Meiosis and the Production of Gametes (cont.) • Meiosis involves two nuclear divisions—meiosis I and meiosis II—that produce four haploid cells. Meiosis is a complex process because it does three important things: 1. reduces chromosomes to the haploid number 2. provides genetic variation 3. ensures the correct distribution of chromosomes into the resulting cells 12.3 Meiosis and the Production of Gametes 4

  24. Cell Division and Reproduction 12.3 Meiosis and the Production of Gametes (cont.) • Meiosis does not always divide the cytoplasm equally between daughter cells. In most male animals, including humans, meiosis produces four equal-sized sperm. 12.3 Meiosis and the Production of Gametes 5

  25. Cell Division and Reproduction 12.3 Meiosis and the Production of Gametes (cont.) • In females, most of the cytoplasm remains in one cell which becomes the ovum. In animal species, the two small cells, called polar bodies, usually break down and disintegrate. In flowering plants, one polar body survives and remains diploid, eventually developing into the endosperm that nourishes the embryo. 12.3 Meiosis and the Production of Gametes 6

  26. End of Section 1

  27. Two strands of the conjugating colonial alga Spirogyra elegans exchange DNA through temporary cytoplasmic bridges, x190. Sexual Reproduction 12.4 Sexual Reproduction in Microorganisms • Prokaryotes reproduce asexually through a process of cell fusion called conjugation, which promotes genetic variation but does not produce offspring. In conjugation, a tube of cytoplasm temporarily connects cells which allows the exchange DNA. Conjugation also occurs in many unicellular eukaryotes. 12.4 Sexual Reproduction in Microorganisms 1

  28. A diagram of alternation of generations shows that the haploid and diploid stages of the same organism often look completely different. Sexual Reproduction 12.4 Sexual Reproduction in Microorganisms (cont.) • The life cycles of organisms that reproduce both asexually and sexually include both haploid and diploid stages, a pattern called alternation of generations. 12.4 Sexual Reproduction in Microorganisms 2

  29. Sexual Reproduction 12.4 Sexual Reproduction in Microorganisms (cont.) • Many fungi and other microorganisms switch from asexual to sexual reproduction in response to changes in their environment. 12.4 Sexual Reproduction in Microorganisms 3

  30. Sexual Reproduction 12.5 Sexual Reproduction in Plants • Plants generally reproduce sexually, although, many plants can also reproduce asexually, and some have even lost the ability to reproduce sexually. Plant life cycles involve alternation of generations. Simple plants, such as mosses, spend most of their lives in the haploid stage. 12.5 Sexual Reproduction in Plants 1

  31. Life cycle of a moss 12.5 Sexual Reproduction in Plants 2

  32. On the underside of a frond of a licorice fern, Polypodium vulgare, the mature spores will be released and fall to the ground. There they will develop into tiny haploid plants. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) • The underside of a fern frond contains reproductive structures in which meiosis produces haploid spores. These spores grow into tiny haploid plants that produce male and female gametes. After fertilization, the zygote grows into a new diploid fern. 12.5 Sexual Reproduction in Plants 3

  33. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) • More complex plants are large diploid structures. Their haploid stage is just a small tissue in their reproductive organs which protect the ova. Wind or symbiotic animals carry the sperm that has been packaged inside tough protective pollen grains to the female organs. 12.5 Sexual Reproduction in Plants 4

  34. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) • The most successful plants are the flowering plants. Haploid cells in the flowers produce the gametes—sperm, ova, or both. At the center of an ovum-producing flower, one or more modified leaves called carpels fuse edge to edge, forming a hollow structure. The base of this structure is the ovary, which contains one or more small structures called ovules where the ova develops. 12.5 Sexual Reproduction in Plants 5

  35. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) • Within each ovule, a specialized cell undergoes meiosis, resulting in the ovum and a large cell containing two nuclei known as polar nuclei. Cells in the anther undergo meiosis, producing four haploid cells resulting in a pollen grain containing two cells—a tube cell and a second cell that divides to produce two haploid sperm nuclei. 12.5 Sexual Reproduction in Plants 6

  36. The carpel and stamen (a) make up the female and male parts, respectively, of a typical flower. The haploid stage in the life cycles of flowering plants is a small part of the flower. Gametes in flowering plants form from specialized cells. In the development of both ova (b) and sperm (c), haploid cells formed by meiosis divide by mitosis before gamete production is complete. 12.5 Sexual Reproduction in Plants 7

  37. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) • Sexual reproduction begins as the anthers shed pollen. The transfer of pollen from anther to carpel is called pollination. Cross-pollination between two different plants of the same species increases genetic variation by combining chromosomes from two parents. 12.5 Sexual Reproduction in Plants 8

  38. Nutrients and other substances in the stigma stimulate the pollen grain to germinate. The pollen tube grows down through the style and ovary wall to the ovule. Double fertilization occurs in the ovule as one sperm fuses with the ovum and the other fuses with the two polar nuclei. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) 12.5 Sexual Reproduction in Plants 9

  39. The zygote develops into the embryo, and the triploid cell develops into the endosperm. The stigma and style shrivel up and may fall off after fertilization. The ovule wall becomes the seed coat, and the ovary wall becomes the fruit. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) 12.5 Sexual Reproduction in Plants 10

  40. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) • Many fruits are carried by the wind or water. Many seeds remain inside fruits, which may be eaten by animals and transported great distances in their digestive systems. 12.5 Sexual Reproduction in Plants 11

  41. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) Each edible fruit is a mature ovary containing the seeds of the plant. Many fruits have structural adaptations for seed dispersal. 12.5 Sexual Reproduction in Plants 12

  42. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) • Several adaptations in flowering plants contribute to their success in widely different environments: 1. the dominance of the diploid stage in the life cycle, which allows development of complex structures 2. the evolution of pollen, which allows transfer of sperm from plant to plant without the need for water 3. the evolution of the seed, which protects the dormant embryo and provides food and protection for the young plant 4. a variety of adaptations that promote pollen and seed dispersal 12.5 Sexual Reproduction in Plants 13

  43. Sexual Reproduction 12.5 Sexual Reproduction in Plants (cont.) (a), Mountain dogwood, Cornus nuttallii, in a pine-sequoia forest; (b), hedgehog cactus, Echinocereus, in a desert; (c), water lily, Nymphaea odorata. 12.5 Sexual Reproduction in Plants 14

  44. Sexual Reproduction 12.6 Sexual Reproduction in Animals • A large majority of animals reproduce sexually. Most animals that reproduce sexually have organs called gonads that produce gametes. These organs include ovaries, which produce ova, and testes (singular: testis), which produce sperm. 12.6 Sexual Reproduction in Animals 1

  45. Sexual Reproduction 12.6 Sexual Reproduction in Animals (cont.) • In many simple animals, such as Hydras, each individual produces both eggs and sperm. Most of these animals, however, are not usually self-fertilizing. A few vertebrates produce both eggs and sperm, but none are known to produce both simultaneously. 12.6 Sexual Reproduction in Animals 2

  46. Sexual Reproduction 12.6 Sexual Reproduction in Animals (cont.) • Most aquatic animals release large numbers of gametes into the water, a process known as spawning, or external fertilization. In contrast, land animals and a few aquatic animals, such as whales, depend on internal fertilizationthat occurs within the body of the female. 12.6 Sexual Reproduction in Animals 3

  47. The male wood frog, Rana sylvatica, deposits sperm over the eggs as the female releases them. Sexual Reproduction 12.6 Sexual Reproduction in Animals (cont.) • Amphibians are intermediate between internal and external fertilization. The male deposits sperm over the eggs as the female releases them into the water greatly increasing the chance of fertilization. 12.6 Sexual Reproduction in Animals 4

  48. Sexual Reproduction 12.6 Sexual Reproduction in Animals (cont.) • Internal fertilization makes reproduction more efficient because the egg is sheltered within the female’s body requiring fewer eggs. Internal fertilization is part of an evolutionary trend among larger, more complex organisms toward fewer gametes and offspring and greater parental care for each offspring. 12.6 Sexual Reproduction in Animals 5

  49. This young grey kangaroo, Macropus, begins its development within its mother’s body. After birth, a young marsupial crawls into its mother’s pouch, attached to a nipple, and completes development. Sexual Reproduction 12.6 Sexual Reproduction in Animals (cont.) • Primitive mammals provide evidence of how mammalian reproduction evolved. • Only two species of mammals lay shelled eggs. • Marsupials, give birth to immature embryos that develop in an open pouch on the outside of the mother’s body. 12.6 Sexual Reproduction in Animals 6

  50. Sexual Reproduction 12.6 Sexual Reproduction in Animals (cont.) • In most animals, sperm are much smaller than eggs. Scanning electron micrograph of human sperm penetrating an egg (color added, x1,210). Only one sperm will fuse with this mature egg, initiating the growth and development of a new person. 12.6 Sexual Reproduction in Animals 7