1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-1 Chapter 3 Development

2. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-2 Stages of the Human Life Cycle Genes orchestrate our physiology after conception through adulthood Development is the process of forming an adult from a single-celled embryo In humans, new individuals form from the union of sex cells or gametes –Sperm from the male and oocyte from the female form a zygote

3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-3 Male Reproductive Tract bladder urethra testis vas deferens epididymis bulbourethral gland seminal vesicle prostate Figure 3.1

4. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-4 Female Reproductive Tract vagina cervix uterus ovary uterine tube Figure 3.2

5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-5 Gametes Form from cell division of germline cells Meiosis is cell division to produce gametes Meiosis has two divisions of the nucleus (Meiosis I and Meiosis II) and produces cells with half the number of chromosomes (haploid)

6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-6 Meiosis Reduces the genetic material by half Why is this necessary? from motherfrom fatherchild meiosis reduces genetic content too much!

7. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-7 Homologous Chromosomes Carry the same genes Pair during Meiosis I Separate in the formation of gametes One copy of each pair is from the mother and one is from the father. Figure 1.2

8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-8 Sexual Reproduction Meiosis and sexual reproduction increases genetic diversity in a population Variation is important in a changing environment Evolution is the genetic change in a population over time

9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-9 Comparison of Mitosis and Meiosis Table 3.1

10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-10 Meiosis Interphase precedes meiosis I Meiosis I Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II Figure 2.13

11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-11 Meiosis I : the reduction division Prophase I (early) (diploid) Prophase I (late) (diploid) Metaphase I (diploid) Anaphase I (diploid) Telophase I (diploid) Nucleus Spindle fibers Nuclear envelope Figure 3.4

12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-12 Early prophase Homologs pair Crossing over occurs Prophase I Late prophase Chromosomes condense Spindle forms Nuclear envelope fragments Figure 3.4

13. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-13 Metaphase I Homolog pairs align along the equator of the cell Figure 3.4

14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-14 Anaphase I Homologs separate and move to opposite poles Sister chromatids remain attached at their centromeres Figure 3.4

15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-15 Telophase I Nuclear membrane reforms Spindle disappears Cytokinesis divides cell Figure 3.4

16. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-16 Meiosis II : like mitosis; sister chromatids separate Prophase II (haploid) Metaphase II (haploid) Anaphase II (haploid) Telophase II (haploid) Four nonidentical haploid daughter cells Figure 3.4

17. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-17 Prophase II Nuclear envelope fragments Spindle forms Figure 3.4

18. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-18 Metaphase II Chromosomes align along equator of cell Figure 3.4

19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-19 Anaphase II Centromeres divide Sister chromatids separate Figure 3.4

20. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-20 Telophase II Nuclear envelopes reform Chromosomes decondense Spindle disappears Cytokinesis divides cells Figure 3.4

21. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-21 Results of Meiosis Gametes Four haploid cells Contain one copy of each chromosome and one allele of each gene Each cell is unique Figure 3.4

22. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-22 Meiosis: Cell Division in Two Parts Result: one copy of each chromosome in a gamete. Haploid Diploid Meiosis I (reduction division) Meiosis II (equational division) Haploid Figure 3.3

23. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-23 Table 3.1

24. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-24 Recombination (crossing over) Occurs in prophase of meiosis I Homologous chromosomes exchange genes Generates diversity a b c d e f A B C D E F A B C D E F a b c d e f Figure 3.5

25. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-25 Recombination (crossing over) Exchange between homologs Occurs in prophase I A B C D E F a b c d e f c d e f A B a b C D E F Letters denote genes and case denotes alleles Figure 3.5

26. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-26 Recombination (crossing over) Creates chromosomes with new combinations of alleles for genes A to F A B C D E F a b c d e f c d e f A B a b C D E F Figure 3.5

27. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-27 Chiasmata In prophase I, crossing over or recombination events create chiasmata. Figure 3.5

28. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-28 Independent Assortment The homolog of one chromosome can be inherited with either homolog of a second chromosome. Figure 3.6

29. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-29 Spermatogenesis: sperm formation Figure 3.7

30. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-30 3.3 Gamete Maturation The cells of the maturing male and female proceed through similar stages but with sex specific terminology and different time tables Males begin manufacturing sperm at puberty and continue throughout life. Females begin meiosis as a fetus and complete meiosis only if a sperm fertilizes and oocyte

31. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-31 Spermatogenesis- formation of sperm cells Begins in the diploid cell- spermatogonium. The spermatogonium divides by mitosis to yield two daughter cells. –One daughter cell will specialize into mature sperm. –One daughter cell will remain a stem cell.

32. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-32 As the mature spermatogonium accumulate cytoplasm, replicate DNA- become primary spermatocytes. Meiosis I- each primary spermatocyte divides forming two equal sized haploid cells called secondary spermatocytes. Meiosis II- each secondary spermatocyte divides to yield two spermatids.

33. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-33 Each spermatid then develops the characteristic tail-flagellum. The base of the tail has many mitochondria that release ATP propelling the sperm in the female tract. After spermatidid differentiation some of the cytoplasm connecting the cells falls away leaving mature tadpole shaped speramtozoa or sperm.

34. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-34 Spermatogenesis Stem cells in testes divide mitotically to produce spermatocytes Spermatocytes divide by meiosis to produce four equal sized haploid spermatids that mature into four sperm. Figure 3.9

35. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-35 Each sperm has a tail, body or midpiece, and a head region. The membrane covered front end- acrosome- enzymes to penetrate the oocyte. In the head DNA is wrapped around proteins- inactive. Built in protections- –Spermatogonia exposed to toxins do not mature into sperm or cannot swim.

36. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-36 Oogenesis Figure 3.11

37. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-37 Oogenesis: Ovum Formation Cells of the ovary divide to form oocytes Oocytes divide by meiosis Unequal cytoplasmic division A discontinuous process –At birth, oocytes are arrested in prophase I –At ovulation, an oocyte continues to metaphase II The four meiotic products produce a functional ovum and three polar bodies.

38. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-38 Fertilization Fertilization is the union of sperm and ovum. The ovum completes meiosis II after fertilization Figure 3.13

39. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-39 Fertilization Hundreds of millions of sperm are deposited in the vagina during sexual intercourse. A sperm cell can survive for up to 3 days but the oocyte can only be fertilized 12-24 hrs. after ovulation. Woman’s body helps sperm reach the oocyte. –Capacitation chemically activates sperm. –Oocyte release an attractant chemical. –Female muscle contractions assist –Moving sperm tails Only 200 sperm come near the oocyte.

40. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-40 The encounter of sperm and oocyte is dramatic. –Wave of electricity –Physical and chemical changes occur over the entire oocyte surface. These chemical reactions prevent additional sperm from entering the ovum. Additional sperm can enter but there is too much genetic material for development to follow.

41. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-41 Usually only the sperm’s head enter the oocyte. The ovum’s nuclear membrane disappears and the two sets of chromosomes called pronuclei approach. Within each pronucleus, DNA replicates. Fertilization completes when the two genetic packages merge. The fertilized ovum is called a zygote.

42. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-42 Multiple Births Dizygotic twins Form from two differ zygotes Two ova are fertilized Same genetic relationship as any siblings Monozygotic twins One ova is fertilized Developing embryo splits during early development Genetically identical

43. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-43 Figure 3.16

44. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-44 Abnormal Chromosome Number Atypical chromosomes account for at least 50 percent of spontaneous abortions, yet only 0.65 percent of newborns have them. Therefore, most embryos and fetuses with atypical chromosomes stop developing before birth. See Table 13.2

45. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-45

46. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-46 An individual whose cells have three copies of each chromosome is a triploid (designated 3N, for three sets of chromosomes). Two-thirds of all triploids result from fertilization of an oocyte by two sperm. The other cases arise from formation of a diploid gamete, such as when a normal haploid sperm fertilizes a diploid oocyte. Triploids account for 17 percent of spontaneous abortions (figure 13.11). Very rarely, an infant survives as long as a few days, with defects in nearly all organs. However, certain human cells may be polyploid. The liver, for example, has some tetraploid (4N) and even octaploid (8N) cells. Polyploidy -most extreme - an entire extra set.

47. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-47

48. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-48 Aneuploidy Cells missing a single chromosome or having an extra one. A normal chromosome number is euploid, which means “good set.” Most autosomal aneuploids (with a missing or extra non-sex chromosome) are spontaneously aborted Intellectual disability is common in aneuploidy because development of the brain is so complex Sex chromosome aneuploidy usually produces milder symptoms. Most children born with the wrong number of chromosomes have an extra chromosome (a trisomy) rather than a missing one (a monosomy).

49. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-49 Nondisjunction The meiotic error that causes aneuploidy is called nondisjunction. In normal meiosis, homologs separate and each of the resulting gametes receives only one member of each chromosome pair. In nondisjunction, a chromosome pair fails to separate at anaphase of either the first or second meiotic division. This produces a sperm or oocyte that has two copies of a particular chromosome, or none, rather than the normal one copy. When such a gamete fuses with its partner at fertilization, the zygote has either 45 or 47 chromosomes, instead of the normal 46.

50. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-50

51. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-51 Most of the 50 percent of spontaneous abortions that result from extra or missing chromosomes are 45, X individuals (missing an X chromosome), triploids, or trisomy 16. About 9 percent of spontaneous abortions are trisomy 13, 18, or 21. More than 95 percent of newborns with atypical chromosome numbers have an extra 13, 18, or 21, or an extra or missing X or Y chromosome. These conditions are all rare at birth—together they affect only 0.1 percent of all children. However, nondisjunction occurs in 5 percent of recognized pregnancies

52. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-52 Stages of Development Table 3.2

53. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-53 Early Development: Ovulation to Implantation Figure 3.14

54. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-54 Cleavage Mitotic cell division; a morula Cells are called blastomeres The developing embryo becomes a blastocyst, a hollow ball of cells

55. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-55 Blastocyst The inner cell mass (ICM) develops into the embryo Other cells become the extraembryonic membranes important for implantation and support of embryonic growth

56. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-56 Gastrulation Primary germ layers form Cells differentiate Supporting structures form –Chorionic villi –Yolk sac –Allantois – By 10 weeks the placenta is fully formed

57. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-57 Germ Layers: Endoderm, Mesoderm, and Ectoderm Figure 3.15

58. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-58 Germ Layers Endoderm: the innermost germ layer develops lining of GI tract liver pancreas thymus Ectoderm: the outermost germ layer develops skin nervous system eye lens Mesoderm: the middle germ layer develops muscle connective tissue blood vessels kidneys

59. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-59 Embryo Develops Figure 3.18

60. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-60 Critical Periods of Development Organs develop at different times: a critical period During its critical period, an organ is vulnerable to toxins, viruses, and genetic abnormalities Altering the normal development may cause birth defects

61. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-61 Critical Periods of Development Figure 3.20

62. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-62 Teratogens Cause birth defects during development Examples –Thalidomide –Cocaine –Cigarettes –Alcohol –Some nutrients –Some viruses

63. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-63 Figure 3.21

64. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-64 Maturation and Aging Genes may impact health throughout life Single gene disorders are expressed early in life and tend to be recessive Adult onset single gene traits are often dominant Interaction between genes and environmental factors Example: malnutrition before birth

65. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-65 Table 3.3

66. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-66 Aging Segmental progeroid syndromes Increases the rate of aging associated changes Inheritance of longevity

67. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-67 Table 3.4