Lecture 6/7

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  1. Asexual Reproduction
    the creation of offspring without fusion of egg and sperm
  2. Sexual Reproduction
    the creation of offspring by fusion of a male gamete (sperm) and female gamete (egg) to form a zygote
  3. 4 types of asexual reproduction
    • Fission: separation of a parent into 2 or more individuals of about the same size
    • Fragmentation: breaking the body into pieces, which develop into adults
    • Budding: new individuals arise from outgrowths of existing ones
    • Parthenogenesis: the development of a new individual from an unfertilized egg
  4. Cost of sexual reproduction
    less offspring
  5. Advantages of sexual reproduction (4)
    • diversity is advantageous in catastrophic events
    • increases in rate of adaptation
    • higher reproductive success, offspring live longer
    • shuffling of genes and elimination of harmful genes
  6. Hermaphroditism
    each individual has male & female reproductive systems
  7. What does meiosis do?
    • reduces the chromosome number in half
    • produces gametes
  8. External vs. Internal Fertilization
    • External fertilization: eggs shed by the female are fertilized by sperm in the external environment
    • Internal fertilization: sperm are deposited in or near the female reproduction tract, fertilization occurs within the tract
  9. Ovulation
    the release of mature eggs at the midpoint of female cycle
  10. Cortical Reaction
    seconds after sperm binds to egg, vesicles beneath the plasma membrane release their contents and form a fertilization envelope
  11. How is the cortical reaction initiated?
    by fusion of egg and sperm
  12. What is the role of the fertilization envelope?
    To prevent polyspermy (entry of multiple sperm nuclei into the egg)
  13. What is a calcium wave? When does it occur?
    • Ca2+ spreads across the egg
    • correlates with the appearance of the fertilization envelope
  14. Capacitation
    when secretions in the mammalian female reproductive tract alter sperm motility and structure
  15. Spermatogenesis vs. Oogenesis (3 differences)
    • all 4 products of meiosis develop into sperm while only one of the 4 becomes an egg
    • spermatogenesis occurs throughout adolescence and adulthood
    • sperm are produce continuously unlike the prolonged interruption in oogenesis
  16. Ovarian Cycle vs. Menstrual Cycle
    changes in the ovaries vs. changes in the uterus
  17. Events in ovarian cycle
    • sequential release of FSH and LH stimulates follicle growth
    • follicular phase ends at ovulation, and secondary oocyte is released
    • after ovulation, the corpus luteum secretes progesterone and estradiol
  18. Events in the menstrual cycle
    • Estradiol and progesterone promote endometrium to thick with blood vessels in preparation for embryo implantation
    • If an embryo is not implants, the endometrium is shed (menstruation)
  19. Steps in Female Reproductive Cycle
    • Ovulation
    • Fertilization
    • Cleavage
    • Implantation
  20. What conditions are necessary for formation of sperm?
    temperature must be lower than body temp.
  21. Oocyte
    a partially developed egg
  22. Follicle
    consists of an oocyte surrounded by support cells
  23. Oogenesis
    process by which an oocyte develops into an ovum
  24. What phase is the oocyte stopped at before birth of the female?
    primary oocyte paused at prophase of meiosis 1
  25. What happens to the oocyte when a female starts puberty?
  26. In vitro fertilization
    eggs are mixed with sperm in culture dishes and the embryo is returned to the uterus at the eight-cell stage
  27. What are the two sex hormones? functions?
    • testosterone & progesterone
    • gamete production
    • development of secondary sex characteristics
  28. Why does cortical reaction occur?
    to prevent polyspermy
  29. Why are testes located outside of the body?
    Because spermatogenesis cannot occur at body temperature
  30. Where does spermatogenesis take place?
    in the seminiferous tubule
  31. When does spermatocyte go from 2n to n?
    when it becomes a secondary spermatocyte
  32. What happens during meiosis II of spermatogenesis?
    4 early spermatids are formed
  33. If thickening of endometrium is blocked, what else is blocked?
    implantation of the fertilized embryo
  34. What do progesterone and estradiol do?
    promote thickening of the endometrium
  35. When does ovulation occur in the reproductive cycle?
    when LH is at its peak
  36. After ovulation occurs, what happens to the follicle tissue?
    the leftover tissue forms the corpus luteum
  37. When progesterone and estradiol levels increase, what happens to the levels of FSH & LH? why?
    • FSH & LH decreases
    • this prevents another egg from maturing when a pregnancy may be under way
  38. Follicular Phase
    growing follicle starts to secrete more and more estradiol
  39. Luteal Phase
    left over corpus luteum starts to secrete progesterone and estradiol
  40. Proliferative Phase
    estradiol signals follicle to grow, uterine tissue starts to thicken and rebuild itself
  41. Secretory Phase
    maximal thickness of endometrium is achieved here
  42. Menstrual Phase
    uterine lining disintegrates, release blood and endometrial tissue
  43. Maternal side of placenta comes from ________ while the fetal side of placenta comes from _______
    endometrium, chorion
  44. Where does fertilization occur?
    In the fallopian tubes
  45. In the blastocyst, the inner cell mass forms the _____ while the trophoblast forms the ______
    • embryo
    • placenta
  46. Low levels of estradiol inhibit what?
    they inhibit secretion of LH and FSH, keeping them at low levels too
  47. What do LH and FSH stand for?
    • Follicle Stimulating Hormone
    • Leutinizing Hormone
  48. What does the hypothalamus secrete in order to signal the anterior pituitary to secrete FSH/LH ?
    GnRH (Gonadotropin-Releasing Hormone)
  49. What inhibits the anterior pituitary from releasing FSH/LH?
    low levels of estradiol
  50. What gland secretes FSH and LH?
    anterior pituitary
  51. What stimulates/inhibits the hypothalamus from releasing GnRH?
    • stimulated by high levels of estradiol
    • inhibited by combination of estradiol/progesterone
  52. Homunculus theory
    In the sperm there lives a little human and after fertilization the little human grows and grows
  53. Morphogenesis involves (2 processes)
    • Gastrulation
    • Organogenesis
  54. What is morphogenesis?
    the process by which cells occupy their appropriate locations
  55. What is gastrulation?
    cells of a blastula are rearranged into a three-layered embryo
  56. What is organogenesis?
    the formation of organs
  57. What are the 3 embryonic germ layers & what do they form?
    • Ectoderm- outer layer
    • Endoderm- lines the digestive tract
    • mesoderm- partly fills space in between endoderm and ectoderm
  58. Blastocyst
    human equivalent of the blastula
  59. Inner Cell Mass
    a cluster of cells at one end of the blastocyst
  60. Trophoblast
    outer epithelial layer of the blastocyst
  61. Function of the trophoblast? What does it generate?
    • initiates implantation
    • generates the placenta
  62. Neurulation
    the formation of primitive CNS structures
  63. Determination
    process by which a cell or group of cells becomes committed to a particular fate
  64. Differentiation
    refers to the resulting specialization in structure and function
  65. What are fate maps?
    diagrams showing organs and other structures that arise from each region of an embryo
  66. How can we create a fate map?
    • can take early stage embryo and label the different cell, map what they will become
    • by imaging - using a green marker to label cells
  67. What happens if you ablate a cell before gastrulation?
    will not affect it
  68. What are germ cells?
    Specialized cells that give rise to sperm or eggs
  69. Conclusion about P. Granules?
    they act as cytoplasmic determinants, fixing germ cell fate at the earliest stage of development
  70. What happens when blastocyst reaches the uterus?
    • blastocyst implants itself into endometrium
    • inner cell mass goes through gastrulation, produces three-layered embryo
    • organogenesis starts
    • neural plate curves inward and forms neural tube
  71. Totipotent Cell
    can develop into all the possible cell types (fertilized egg)
  72. Pluripotent Cell
    can develop into some cells (committed germ cell)
  73. The two ways a cell decides to become something else?
    • #1: mother cell gives each daughter different materials, intracellular method (extreme case in c. elegant)
    • #2: a group of cells tells other cells what to do
  74. How can cells influence other cells?
    signaling molecules from the organizer induce the host cell to adopt different fates
  75. What kind of signaling is involved when cell sends signals to other cells to do something?
    Paracrine signaling
  76. What does ZPA do? How many in a regular cell?
    • only 1 in a regular cell
    • produces an inductive signal that conveys positional info indicating “posterior”
  77. Is the neural tube formed only by grafted cells?
    No, the graft also induces transformations in the host tissue and changes it as well
  78. What do AER and ZPA stand for?
    • AER = apical ectodermal ridge
    • ZPA = sone of polarizing activity
  79. What is the first stage in development after the embryo has been fertilized?
  80. What happens during cell Cleavage?
    rapid cell division
  81. During Cleavage, __________ increases but ______ stays the same
    • cell #
    • volume
  82. Where does Cleavage take place?
    in the fallopian tube
  83. How are genetically identical twins made?
    • clones from the same egg
    • when embryo is split during early development
    • early blastocyst splits into two
  84. How are fraternal twins made?
    release and fertilization of two different eggs
  85. How do fraternal and identical twins each deal with the placenta?
    • identical - share the same one, fight for nutrients
    • fraternal- two placenta
  86. How are P. Granules distributed in a newly fertilized egg?
    they all move to the posterior end before the first cleavage division
  87. Why can C. Elegans not have monozygotic twins?
    because there is no grace period, the cells are committed early in development and P. Granules are not distributed equally
  88. Asymmetric Cell Division
    • the two cells do not inherit the same things
    • happens at the expense of becoming another tissue
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Lecture 6/7
2015-04-24 04:02:33
Lecture 6: Animal Reproduction Lecture 7: Animal Development
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