1. Human Genetics: concepts and applications 5th edition Ricki Lewis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 3 Development

2. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-2 Development the process of forming an adult from a single-celled embryo Cell division Determination Differentiation

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

4. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-4 Male reproductive tract bladder urethra testis vas deferens epididymis bulbourethral gland seminal vesicle prostate

5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-5 Sperm cells are made in the seminiferous tubules of the testes (male gonads) The prostate gland, seminal vesicles, and bulbourethral glands add secretions to form the seminal fluid Sperm mature and are stored in the epididymis (attached to each gonad) They leave through the ductus deferens and then the urethra

6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-6 Female reproductive tract vagina cervix uterus ovary Fallopian tube

7. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-7 Oocytes mature in the ovaries (female gonads) Each individual oocyte is surrounded by nourishing follicle cells, and each ovary houses oocytes in different stages of development Each month, an ovary releases a mature oocyte into the uterine/fallopian tube –If the oocyte is fertilized, it continues to the uterus where it implants then divides and develops –If it is not fertilized, the body expels it, along with the uterine-lining via the menstrual flow

8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-8 If the oocyte encounters a sperm cell the two join forming a fertilized OVUM which will then undergo a series of rapid cell division while moving through the tube and within days nestles into the lining of the uterus Hormones control the cycle of oocyte development, the menstrual cycle, and the preparation of the uterus to nuture a fertilized ovum

9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-9 Replication of chromosomes Replication is the process of duplicating a chromosome Occurs prior to division Replicated copies are called sister chromatids Held together at centromere

10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-10 Meiosis a cell division forming gametes Goal: reduce genetic material by half Why? from momfrom dadchild meiosis reduces genetic content too much!

11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-11 The cell division that produces gametes with half the number of chromosomes Occurs in special cells called germline cells Maintains the chromosome number of a species over generations Ensures genetic variability via the processes of independent assortment and crossing over of chromosomes

12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-12 Meiosis consists of two divisions –Meiosis I= The reduction division –Reduces the number of chromosomes from 46 to 23 –Meiosis II= The equational division –Produces four cells from the two produced in Meiosis I Note = Each division contains a prophase, a metaphase, an anaphase and a telophase

13. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-13 Meiosis: cell division in two parts Homologs separate Sister chromatids separate Result: one copy of each chromosome in a gamete. Haploid Diploid Meiosis I (reduction division) Meiosis II (equational division) Haploid

14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-14 Diploid Haploid

15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-15 Diploid Meiosis I (reduction division) Diploid Haploid

16. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-16 Diploid Haploid Meiosis I (reduction division) Diploid Haploid

17. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-17 Diploid Haploid Meiosis I (reduction division) Meiosis II (equational division) Diploid Haploid

18. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-18 Diploid Haploid Meiosis I (reduction division) Meiosis II (equational division) Haploid Diploid Haploid

19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-19 Meiosis Animation

20. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-20 A replicated chromosome Homologs separate in meiosis I and therefore different alleles separate. homologs same genes maybe different alleles sister chromatids same genes same alleles Gene X

21. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-21 Meiosis I : the reduction division

22. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-22 Prophase I Early prophase Homologs pair. Crossing over occurs. Late prophase Chromosomes condense. Spindle forms. Nuclear envelope fragments.

23. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-23 Metaphase I Homolog pairs align along the equator of the cell. The random alignment pattern determines the combination of maternal and paternal chromosomes in the gametes

24. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-24 Anaphase I Homologs separate and move to opposite poles. Sister chromatids remain Attached at their centromeres.

25. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-25 Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two.

26. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-26 Interkinesis A short interphase between the two meiotic divisions Chromosomes unfold into very thin threads Proteins are manufactured However, DNA is NOT replicated a second time

27. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-27 Meiosis II Only one homolog of each chromosome is present in the cell. Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. Sister chromatids carry identical genetic information. Gene X

28. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-28 Meiosis II : the equational division Prophase II (haploid) Metaphase II (haploid) Anaphase II (haploid) Telophase II (haploid) Four nonidentical haploid daughter cells

29. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-29 Prophase II Nuclear envelope fragments. Chromosomes are again condensed and visible Spindle forms.

30. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-30 Metaphase II Chromosomes align along equator of cell.

31. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-31 Anaphase II Sister chromatids separate and move to opposite poles. Centromeres divide

32. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-32 Telophase II Nuclear envelope assembles. Chromosomes decondense (uncoil). Spindle disappears. Cytokinesis divides cell into two.

33. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-33 Results of meiosis Gametes Four haploid cells One copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome

34. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-34 MitosisMeiosis Number of divisions 1 2 Number of daughter cells 24 Genetically identical? YesNo Chromosome #Same as parentHalf of parent WhereSomatic cellsGermline cells WhenThroughout lifeAt sexual maturity RoleGrowth and repairSexual reproduction

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36. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-36 Recombination (crossing over) Occurs in prophase of meiosis I Generates diversity Creates chromosomes with new combinations of alleles for genes A to F. a b c d e f A B C D E F A B C D E F a b c d e f

37. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-37 Recombination (crossing over) Occurs in prophase of meiosis I Generates diversity Letters denote genes Case denotes alleles 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

38. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-38 Recombination (crossing over) Occurs in prophase of meiosis I Generates diversity Letters denote genes Case denotes alleles 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

39. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-39 Chiasmata Crossing over or recombination events create chiasmata.

40. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-40 Independent assortment The homolog of one chromosome can be inherited with either homolog of a second chromosome.

41. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-41 Mitosis vs. Meiosis Animation

42. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-42 Spermatogenesis Stem cells in testes divide mitotically to create a pool of spermatocytes. Spermatogenesis is the process of forming the mature sperm. Meiosis produces four spermatids.

43. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-43 A diploid spermatogonium divides by mitosis to produce a stem cell and another cell that specializes into a primary spermatocyte In meiosis I, the primary spermatocyte produces two haploid secondary spermatocytes In meiosis II, each secondary spermatocyte produces two haploid spermatids Spermatids then mature into a tad-pole shaped spermatozoa

44. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-44 Spermatogenesis: sperm formation

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

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

48. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-48 Oogenesis A diploid oogonium divides by mitosis to produce a stem cell and another cell that specializes into a primary oocyte In meiosis I, the primary oocyte divides unequally forming a small polar body and a large secondary oocyte In meiosis II, the secondary oocyte divides to form another polar body and a mature haploid ovum

49. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-49 Oogenesis: ovum formation One of four meiotic products becomes an ovum. The three remaining meiotic products are polar bodies.

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 Unlike spermatogenesis, oogenesis is a discontinuous process A female begins meiosis when she is a fetus –Oocytes arrest at prophase I until puberty –After puberty, meiosis I continues in one or several oocytes each month but halts again at metaphase II –Meiosis is only completed if the ovum is fertilized

52. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-52 Oogenesis Oogonium (diploid) Mitosis Primary oocyte (diploid) Meiosis I Secondary oocyte (haploid) Meiosis II (if fertilization occurs) First polar body may divide (haploid) Polar bodies die Ovum (egg) Second polar body (haploid) a A X X a X A X a X a X Mature egg A X A X

53. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-53

54. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-54 Oogenesis versus Spermatogenisis

55. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-55 Maturation of the Follicle and Oocyte

56. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-56 Fertilization Fertilization is the joining of sperm and ovum. Meiosis II in the ovum is completed at the time of fertilization forming one ovum and one polar body. Following fertilization, chemical reactions occur preventing additional sperm from entering the ovum.

57. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-57 Union of sperm and ovum In the female, sperm are capacitated and drawn to the secondary oocyte Acrosomal enzymes aid sperm penetration Chemical and electrical changes in the oocyte surface block entry of more sperm The two sets of chromosomes fuse into one nucleus, forming the zygote

58. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-58

59. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-59 Stages of development

60. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-60 Cleavage Mitotic cell division creates more cells. Cells are called blastomeres. A period of frequent mitotic divisions –Resulting cells are called blastomeres Developing embryo becomes a solid ball of 16+ cells called a morula The ball of cells hollows out to form a blastocyst

61. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-61 Blastocyst The developing embryo becomes a hollow ball of cells and is called a blastocyst. The cells around the ICM become the extraembryonic membranes role in implantation supports embryo’s growth Group of cells within the hollow space forms the inner cell mass (ICM). develops into the embryo.

62. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-62 Consists of two main parts –Inner cell mass (ICM), which develops into the embryo –Trophoblast, which develops into the placenta Implantation in the uterus occurs around day 7 Certain blastocyst cells secrete human chorionic gonadotropin (hCG) –A sign of pregnancy

63. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-63 Early development: ovulation to implantation Figure 3.14

64. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-64 Germ layers: endoderm, mesoderm and ectoderm

65. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-65 Gastrulation The primary germ layers form in the second week after fertilization –Ectoderm (outermost layer) –Mesoderm (middle layer) –Endoderm (innermost layer) This three-layered structure is the gastrula Cells in each germ layer begin to form specific organs

66. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-66 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

67. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-67 Supportive Structures Structures that support and protect the embryo include: –Chorionic villi –Yolk sac –Allantois –Umbilical cord –Amniotic sac By 10 weeks the placenta is fully formed

68. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-68 Twins Dizygotic twins two ova + two sperm Developing embryo splits during early development Monozygotic twins one ovum + one sperm Same genetic relation as any siblings Genetically identical - Arise from two fertilized ova - Same genetic relationship as any two siblings -Arise from a single fertilized ovum -Embryo splits early during development -Twins may share supportive structures

69. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-69

70. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-70

71. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-71 The Embryo Develops Organogenesis is the transformation of the simple three germ layers into distinct organs During week 3, a band called the primitive streak appears along the back of the embryo This is followed rapidly by the notochord, neural tube, heart, central nervous system, limbs, digits, and other organ rudiments By week 8, all the organs that will be present in the newborn have begun to develop –The prenatal human is now called a fetus

72. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-72

73. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-73 The Fetus Grows During the fetal period, structures grow, specialize and begin to interact Bone replaces cartilage in the skeleton Body growth catches up with the head Sex organs become more distinct In the final trimester, the fetus moves and grows rapidly, and fat fills out the skin The digestive and respiratory systems mature last

74. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-74 Critical periods of development Organs develop at different times in development: a critical period. During its critical period, an organ is vulnerable to toxin, viruses, and genetic abnormalities. Altering the normal development may cause birth defects.

75. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-75 The time when a particular structure is sensitive to damage is called its critical period Birth defects can result from a faulty gene or environmental insult Most birth defects develop during the embryonic period These are more severe than those that arise during the fetal period

76. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-76 Fig. 3.19

77. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-77 Teratogens are agents causing birth defects Drugs Thalidomide limb defects Cocaine stroke, nervous system Cigarettes poor growth, low birth weight Alcohol fetal alcohol syndrome (FAS) Nutrients folic acid deficiency neural tube defects vitamin C excess scurvy, immune effects Viral infection rubella deafness, cataracts, heart herpes death, CNS damage, skin lesions HIV HIV infection, prematurity

78. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-78 Fetal Alcohol Syndrome

79. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-79 Onset of genetic disorders Is the time when a disorder is first observed. Many disorders have a characteristic time of onset. Time of onsetDisorder PrenatalPolydactyly BirthPhenylketonuria 10 yearsWilson disease 20 yearsMarfan syndrome 30 yearsBreast cancer 40 yearsPattern baldness 50 yearsAlzheimer disease

80. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-80 Clones A clone is a collection organisms derived from the same original cell. Genetically identical Phenotype may differ because of different life history. Calves cloned share genes. variation in coat patterns reflect migration of cells during development

81. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-81 Aging Genes may impact health throughout life Single-gene disorders that strike in childhood tend to be recessive Adult-onset single-gene traits are often dominant Interaction between genes and environmental factors –Example: Malnutrition before birth

82. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-82 Genes control aging both passively and actively A few single-gene disorders can speed the signs of aging Segmented progeroid syndromes –Hutchinson-Guilford syndrome

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84. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3-84 Is Longevity Inherited? Aging reflects genetic activity plus a lifetime of environmental influences Human chromosome 4 houses longevity genes –Genome-wide screens of 100-year olds are identifying others Adoption studies compare the effects of genes vs. the environment on aging

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