Reproduction and Development in Animals

1. CHAPTER 26 Reproduction and Development Figures 26.1 – 26.2

2. During ejaculation, a man releases up to 500 million sperm, only one of which may fertilize an egg • You have trillions of cells in your body, and they all arose from one original cell

3. An American woman is 4 times more likely to deliver triplets today than 25 years ago • Even though a woman is born with up to half a million developing gametes, she will only use about 500 during her lifetime

4. BIOLOGY AND SOCIETY:RISE OF THE SUPERTWINS • On November 19, 1997, news reports heralded the arrival of the Iowa septuplets Figure 26.1

5. Other sets of multiple births soon followed • What accounted for the sudden rash of multiple births?

6. All of these multiple births were by women who had taken fertility drugs because they couldn’t become pregnant naturally • Couples turn to fertility drugs to overcome their natural reproductive limitations

7. UNIFYING CONCEPTS OF ANIMAL REPRODUCTION • Reproduction is the creation of new individuals from existing ones

8. Asexual Reproduction • In asexual reproduction • One parent produces genetically identical offspring

9. Binary fission • Is the simplest type of asexual reproduction • Involves a single parent cell splitting through mitosis into two genetically identical offspring cells

10. Some multicellular organisms reproduce by a similar means called fission, in which one organism splits into two or more individuals Figure 26.2a

11. Fragmentation is the breaking of a parent body into several pieces • Regeneration, which follows fragmentation, is the regrowth of a whole animal from the pieces

12. Budding • Is the splitting off of new individuals from existing ones Figure 26.2b

13. Asexual reproduction has a number of advantages • It allows a species to perpetuate itself if its individual members are sessile or isolated from one another • It allows organisms to multiply quickly

14. One potential disadvantage of asexual reproduction is that it produces genetically uniform populations

15. Sexual Reproduction • Sexual reproduction • Involves the fusion of gametes (sperm and egg) from two parents • Increases the genetic variability among offspring

16. Some animals can reproduce both sexually and asexually Figure 26.3a

17. Some species are hermaphrodites with both male and female reproductive systems Figure 26.3b

18. The mechanics of fertilization play an important part in sexual reproduction

19. Many organisms use external fertilization, in which parents discharge their gametes into the water, where fertilization occurs Figure 26.3c

20. Other organisms use internal fertilization, which occurs within the female’s body • Internal fertilization requires copulation, or sexual intercourse

21. HUMAN REPRODUCTION • Both sexes of humans have • A pair of gonads, the organs that produce gametes • Ducts to store and deliver the gametes • Structures to facilitate copulation

22. Female Reproductive Anatomy • The ovaries • Are the site of gamete production in human females Ovaries Oviduct Follicles Corpus luteum Uterus Wall of uterus Endometrium (lining of uterus) Cervix (“neck” of uterus) Vagina Figure 26.4

23. The ovaries contain follicles • Each follicle consists of a single developing egg cell surrounded by layers of cells that nourish and protect it • The follicles also produce estrogen, the female sex hormone

24. Ovulation • Is the process by which an egg cell is ejected from the follicle Figure 26.5

25. The egg enters the oviduct, which is a tube in which cilia sweep the egg toward the uterus

26. The uterus is the actual site of pregnancy • The cervix, the narrow neck at the bottom of the uterus, opens into the vagina, or birth canal • During copulation, the vagina serves as a repository for sperm

27. Female reproductive anatomy Oviduct Ovary Rectum (digestive system) Uterus Bladder (excretory system) Pubic bone Urethra (excretory system) Cervix Vagina Shaft Clitoris Glans Prepuce Labia minora Labia majora Vaginal opening Figure 26.6

28. Male Reproductive Anatomy • The penis • Contains erectile tissue

29. The testes • Are the male gonads, enclosed in a sac called the scrotum • Produce sperm

30. Several glands • Contribute to the formation of the fluid that carries, nourishes, and protects sperm • Semen • Consists of this fluid and sperm

31. Male reproductive anatomy, side view Bladder (excretory system) Seminal vesicle Pubic bone Rectum (digestive system Erectile tissue of penis Vas deferens Urethra Prostate gland Vas deferens Glans of penis Epididymis Testis Prepuce Scrotum Figure 26.7a

32. Male reproductive anatomy, front view Seminal vesicle (behind bladder) Bladder (excretory system) Prostate gland Urethra Erectile tissue of penis Vas deferens Scrotum Epididymis Glans of penis Testis Figure 26.7b

33. Gametogenesis • Gametogenesis • Is the production of gametes • Human gametes • Are haploid cells that develop by meiosis

34. Oogenesis • Oogenesis is the development of eggs within the ovaries Diploid cell in embryo Differentiation and onset of meiosis I Ovary Primary oocyte, arrested in prophase of meiosis I; present at birth Completion of meiosis I and onset of meiosis II Corpus luteum First polar body Secondary oocyte, Growing follicle arrested at metaphase of meiosis II; released from ovary Entry of sperm triggers completion of meiosis II Mature follicle Second polar body Ovulation Ruptured follicle Ovum (haploid) Sperm Figure 26.8

35. Spermatogenesis • Spermatogenesis • Is the formation of sperm cells

36. Epididymis Penis Testis Scrotum Diploid cell Testis Differentiation and onset of meiosis I Seminiferous tubule Primary spermatocyte Cross section of seminiferous tubule Meiosis I completed Secondary spermatocyte Meiosis II Developing spermatids Differentiation Sperm cells (haploid) Center of seminiferous tubule Figure 26.9

37. The Female Reproductive Cycle • Human females have a reproductive cycle, a recurring series of events that produces gametes, makes them available for fertilization, and prepares the body for pregnancy

38. The female reproductive cycle involves two sets of changes • The ovarian cycle controls the growth and release of an ovum • The menstrual cycle prepares the uterus for possible implantation of an embryo

39. Hormones • Synchronize cyclical changes in the ovaries and uterus

40. The female reproductive cycle Control by hypothalamus Inhibited by combination of estrogen and progesterone Hypothalamus Stimulated by high levels of estrogen Releasing hormone Anterior pituitary (a) 1 Pituitary hormones in blood 4 (b) FSH stimulates follicle to grow 2 LH peak triggers ovulation Ovarian cycle 5 Growing follicle Mature follicle Ovulation Corpus luteum Degenerating corpus luteum (c) Estrogen secreted by growing follicle Progesterone and estrogen secreted by remnant of follicle Figure 26.10a–c

41. Ovarian hormones in blood Peak causes LH surge 3 7 Estrogen Progesterone 6 (d) Progesterone and estrogen promote thickening of endometrium Low levels trigger menstruation Menstrual cycle Endometrium (e) Figure 26.10d, e Menstruation

42. REPRODUCTIVE HEALTH • Two issues of human reproductive health • Contraception • Transmission of disease

43. Contraception • Contraception • Is the deliberate prevention of pregnancy

44. There are many forms of contraception, each with varying degrees of reliability Figure 26.11

45. Contraceptive methods and their effectiveness Table 26.1

46. Sexually Transmitted Diseases • Sexually transmitted diseases (STDs) • Are contagious diseases spread by sexual contact

47. Viral STDs, such as AIDS, genital herpes, and genital warts, cannot be cured but can be controlled by medications

48. STDs caused by bacteria, protozoans, and fungi are generally curable with drugs Table 26.2

49. REPRODUCTIVE TECHNOLOGIES • Reproductive technologies • Can help solve problems related to the inability to conceive a child

50. Infertility • Infertility • Is the inability to have children after one year of trying • Is most often due to problems in the man, such as underproduction of sperm or impotence