1. Chapter 7 Development and Sex Determination
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

2. Sexual Differentiation in Humans
Begins in the 7th week of development
Is influenced by genetic and environmental factors
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

3. Human Reproductive System
Zygote fertilized egg (diploid)
Gametes unfertilized germ cells
Sperm male gamete (haploid)
Oocyte female gamete (haploid)
Gonads organs where gametes and sex hormones are produced (testes and ovaries)
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

4. Male Reproductive System
Fig. 7.1
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

5. Spermatogenesis
Fig. 7.2
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

6. Spermatogenesis
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

7. Spermatogenesis
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

8. Credit: © Dr. Richard Kessel & Dr. Gene Shih/Visuals Unlimited
99917
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Seminiferous tubule filled with sperm. SEM X335.

9. Credit: © Dr. David Phillips/Visuals Unlimited
Human sperm. TEM.
Credit: © Dr. David Phillips/Visuals Unlimited
99895
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

10. Credit: © Dr. David Phillips/Visuals Unlimited
Human sperm. TEM.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

11. Female Reproductive System
Fig. 7.3
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

12. Ovary Stepped Art Fig. 7-4, p.155
FIGURE 7.4 Cross section of an ovary showing follicles in various stages of development. The photomicrograph at the right shows a secondary oocyte being released from the surface of the ovary. This oocyte will enter the fallopian tube and move toward the uterus.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-4, p.155

13. released from meiosis I. A cell layer is forming around
Primary oocyte, not yet
released from meiosis I. A
cell layer is forming around
it. A follicle consists of the
cell layer and the oocyte.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Ovary
Primordial
follicle
FIGURE 7.4 Cross section of an ovary showing follicles in various stages of development. The photomicrograph at the right shows a secondary oocyte being released from the surface of the ovary. This oocyte will enter the fallopian tube and move toward the uterus.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-4, p.155

14. released from meiosis I. A cell layer is forming around
Primary oocyte, not yet
released from meiosis I. A
cell layer is forming around
it. A follicle consists of the
cell layer and the oocyte.
A transparent and
somewhat elastic layer,
the zona pellucida,
starts forming around
the primary oocyte.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Ovary
Primordial
follicle
FIGURE 7.4 Cross section of an ovary showing follicles in various stages of development. The photomicrograph at the right shows a secondary oocyte being released from the surface of the ovary. This oocyte will enter the fallopian tube and move toward the uterus.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-4, p.155

15. released from meiosis I. A cell layer is forming around
Primary oocyte, not yet
released from meiosis I. A
cell layer is forming around
it. A follicle consists of the
cell layer and the oocyte.
A transparent and
somewhat elastic layer,
the zona pellucida,
starts forming around
the primary oocyte.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Ovary
Primordial
follicle
FIGURE 7.4 Cross section of an ovary showing follicles in various stages of development. The photomicrograph at the right shows a secondary oocyte being released from the surface of the ovary. This oocyte will enter the fallopian tube and move toward the uterus.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-4, p.155

16. released from meiosis I. A cell layer is forming around
Primary oocyte, not yet
released from meiosis I. A
cell layer is forming around
it. A follicle consists of the
cell layer and the oocyte.
A transparent and
somewhat elastic layer,
the zona pellucida,
starts forming around
the primary oocyte.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Ovary
Mature follicle.
Meiosis I is over.
The secondary
oocyte and first
polar body are
now formed.
Primordial
follicle
First polar body
Secondary oocyte
FIGURE 7.4 Cross section of an ovary showing follicles in various stages of development. The photomicrograph at the right shows a secondary oocyte being released from the surface of the ovary. This oocyte will enter the fallopian tube and move toward the uterus.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-4, p.155

17. released from meiosis I. A cell layer is forming around
Primary oocyte, not yet
released from meiosis I. A
cell layer is forming around
it. A follicle consists of the
cell layer and the oocyte.
A transparent and
somewhat elastic layer,
the zona pellucida,
starts forming around
the primary oocyte.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Ovary
Mature follicle.
Meiosis I is over.
The secondary
oocyte and first
polar body are
now formed.
Primordial
follicle
First polar body
Secondary oocyte
FIGURE 7.4 Cross section of an ovary showing follicles in various stages of development. The photomicrograph at the right shows a secondary oocyte being released from the surface of the ovary. This oocyte will enter the fallopian tube and move toward the uterus.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Ovulation. The mature follicle ruptures, releasing
the secondary oocyte and first polar body.
Stepped Art
Fig. 7-4, p.155

18. released from meiosis I. A cell layer is forming around
Primary oocyte, not yet
released from meiosis I. A
cell layer is forming around
it. A follicle consists of the
cell layer and the oocyte.
A transparent and
somewhat elastic layer,
the zona pellucida,
starts forming around
the primary oocyte.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Ovary
Mature follicle.
Meiosis I is over.
The secondary
oocyte and first
polar body are
now formed.
Primordial
follicle
First polar body
Secondary oocyte
FIGURE 7.4 Cross section of an ovary showing follicles in various stages of development. The photomicrograph at the right shows a secondary oocyte being released from the surface of the ovary. This oocyte will enter the fallopian tube and move toward the uterus.
A corpus
luteum forms
from remnants
of the ruptured
follicle.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Ovulation. The mature follicle ruptures, releasing
the secondary oocyte and first polar body.
Stepped Art
Fig. 7-4, p.155

19. released from meiosis I. A cell layer is forming around
Primary oocyte, not yet
released from meiosis I. A
cell layer is forming around
it. A follicle consists of the
cell layer and the oocyte.
A transparent and
somewhat elastic layer,
the zona pellucida,
starts forming around
the primary oocyte.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer.
Ovary
Mature follicle.
Meiosis I is over.
The secondary
oocyte and first
polar body are
now formed.
Primordial
follicle
First polar body
Secondary oocyte
The corpus
luteum breaks
down when
the woman
doesn’t get
pregnant.
FIGURE 7.4 Cross section of an ovary showing follicles in various stages of development. The photomicrograph at the right shows a secondary oocyte being released from the surface of the ovary. This oocyte will enter the fallopian tube and move toward the uterus.
A corpus
luteum forms
from remnants
of the ruptured
follicle.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Ovulation. The mature follicle ruptures, releasing
the secondary oocyte and first polar body.
Stepped Art
Fig. 7-4, p.155

20. Credit: © Gary Martin/Visuals Unlimited
Ovulation
Credit: © Gary Martin/Visuals Unlimited
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

21. Timing of Meiosis and Spermatogenesis
Large numbers of sperm are in constant production
Four functional, equally-sized gametes per primary spermatocyte
Over a lifetime a male produces billions of sperm
Spermatogenesis takes approximately 48 days
Each ejaculation can contain m sperm
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

22. Timing of Meiosis and Oogenesis
Unequal cytoplasmic division and produces 1 large functional gamete and 3 nonfunctional polar bodies
Primary oocytes are produced prior to birth and are held in meiosis I
After puberty, one oocyte completes meiosis I each monthly cycle, starts meiosis II and arrests at metaphase of meiosis II
If fertilization occurs, it completes meiosis II
Time for complete cycle is 12–50 years
Release about 450 oocytes in a lifetime
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

23. Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

24. 1 spermatogonium  4 mature sperm
1 oogonium  1 oocyte + 3 polar bodies
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

25. Fertilization to Implantation
Fertilization is the fusion of two gametes to produce a zygote
Zygote is moved by cilia in the lining of the oviduct to the uterus
The zygote divides by mitosis
Forms a early embryonic stage, the blastocyst
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

26. Fertilization Oviduct Ovary Uterus Ovulation Opening of cervix Vagina
Sperm enter vagina
FIGURE 7.5 (a–b) In fertilization, many sperm surround the secondary oocyte and secrete enzymes that dissolve the outer barriers surrounding the oocyte. Only one sperm enters the egg. Penetration stimulates the oocyte to begin meiosis II.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-5b, p.157

27. Fertilization Oviduct Ovary Follicle cell Uterus Ovulation
Opening of cervix
Egg nucleus
Vagina
Sperm enter vagina
Zona pellucida
FIGURE 7.5 (a–b) In fertilization, many sperm surround the secondary oocyte and secrete enzymes that dissolve the outer barriers surrounding the oocyte. Only one sperm enters the egg. Penetration stimulates the oocyte to begin meiosis II.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-5b, p.157

28. Fertilization Oviduct Ovary Follicle cell Uterus Ovulation
Opening of cervix
Egg nucleus
Vagina
Sperm enter vagina
Zona pellucida
FIGURE 7.5 (a–b) In fertilization, many sperm surround the secondary oocyte and secrete enzymes that dissolve the outer barriers surrounding the oocyte. Only one sperm enters the egg. Penetration stimulates the oocyte to begin meiosis II.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-5b, p.157

29. Fusion of sperm nucleus with egg nucleus
Fertilization
Oviduct
Ovary
Follicle cell
Uterus
Ovulation
Opening of cervix
Egg nucleus
Vagina
Sperm enter vagina
Zona pellucida
FIGURE 7.5 (a–b) In fertilization, many sperm surround the secondary oocyte and secrete enzymes that dissolve the outer barriers surrounding the oocyte. Only one sperm enters the egg. Penetration stimulates the oocyte to begin meiosis II.
Nuclei fuse
Fusion of sperm nucleus with egg nucleus
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-5b, p.157

30. Fusion of sperm nucleus with egg nucleus
Fertilization
Oviduct
Ovary
Follicle cell
Uterus
Ovulation
Opening of cervix
Egg nucleus
Vagina
Sperm enter vagina
Zona pellucida
FIGURE 7.5 (a–b) In fertilization, many sperm surround the secondary oocyte and secrete enzymes that dissolve the outer barriers surrounding the oocyte. Only one sperm enters the egg. Penetration stimulates the oocyte to begin meiosis II.
Nuclei fuse
Fusion of sperm nucleus with egg nucleus
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-5b, p.157

31. Credit: © Dr. David Phillips/Visuals Unlimited
350626
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Sperm entering the oviduct. SEM X500.

32. Credit: © Dr. David Phillips/Visuals Unlimited
167105
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fertilization. SEM X4700.

33. Cleavage and gastrulation (Xenopus embryo)
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

34. Blastocyst Mass of approximately 100 cells It has two parts
Inner cell mass gives rise to the embryo
Trophoblast gives rise to surrounding membranes
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

35. Implantation The trophoblast attaches to the endometrium of the uterus
Villi (finger like projections) grow into the endometrium and anchor the embryo
After approximately 12 days, the trophoblast has formed the chorion
Chorion secretes human chorionic gonadotropin (hCG) which maintains the uterine lining (pregnancy test)
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

36. Placenta Highly vascular Formed from the chorionic villi
Allows oxygen, wastes, nutrients, and other molecules to be exchanged between the mother and child
Membranes that connect the embryo to the placenta form the umbilical cord
Source of stem cells
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

37. Fertilization Implantation Endometrium Stepped Art Fig. 7-6a-e, p.159
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-6a-e, p.159

38. Fertilization Implantation Endometrium DAYS 1-2 Stepped Art
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
DAYS 1-2
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-6a-e, p.159

39. Fertilization Implantation Endometrium DAYS 1-2 DAY 3 Stepped Art
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
DAYS 1-2
DAY 3
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-6a-e, p.159

40. Fertilization Implantation Endometrium DAYS 1-2 DAY 3 DAY 4
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
DAYS 1-2
DAY 3
DAY 4
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-6a-e, p.159

41. Fertilization Implantation Endometrium DAYS 1-2 DAY 3 DAY 4 DAY 5
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
DAYS 1-2
DAY 3
DAY 4
DAY 5
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-6a-e, p.159

42. Fertilization Implantation Endometrium Inner cell mass DAYS 1-2 DAY 3
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
DAYS 1-2
DAY 3
DAY 4
DAY 5
DAY 5
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-6a-e, p.159

43. Trophoblast (surface layer of cells of the blastocyst)
Fertilization
Trophoblast (surface layer of cells of the blastocyst)
Implantation
Endometrium
Endometrium
blastocoel
Inner cell mass
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
Inner cell mass
Uterine cavity
DAYS 1-2
DAY 3
DAY 4
DAY 5
DAY 5
DAYS 6-7
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-6a-e, p.159

44. FIGURE 7. 6 From fertilization through implantation
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-6f-h, p.159

45. Start of embryonic disk Start of amniotic cavity Start of yolk sac
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
Start of
yolk sac
DAYS 10–11
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-6f-h, p.159

46. Start of embryonic disk Blood-filled spaces Start of amniotic cavity
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
Start of
chorionic cavity
Start of
yolk sac
DAYS 10–11
DAY 12
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-6f-h, p.159

47. Chorion Chorionic villi Start of embryonic disk Blood-filled spaces
Chorionic cavity
Amniotic
cavity
Start of
amniotic cavity
FIGURE 7.6 From fertilization through implantation. A blastocyst forms and its inner cell mass gives rise to a disk-shaped early embryo. As the blastocyst implants into the uterus, cords of chorionic cells start to form. When implantation is complete, the blastocyst is buried in the endometrium.
Connective
tissue
Start of
chorionic cavity
Start of
yolk sac
Yolk sac
DAYS 10–11
DAY 12
DAY 14
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Stepped Art
Fig. 7-6f-h, p.159

48. WEEK 4 WEEKS 5–6 Yolk sac Connecting stalk Embryo Fig. 7-7a1, p.160
FIGURE 7.7 Stages of human development. (a) Human embryo 4 weeks after fertilization.
WEEK 4
WEEKS 5–6
Yolk sac
Connecting stalk
Embryo
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7a1, p.160

49. Forebrain Future lens Pharyngeal arches Developing heart
Upper limb bud
Somites
FIGURE 7.7 Stages of human development. (a) Human embryo 4 weeks after fertilization.
Neural tube
forming
Lower limb
bud
Tail
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7a2, p.160

50. growth of other regions Retinal pigment
Head growth exceeds
growth of other regions
Retinal pigment
Future external ear
Upper limb differentiation (hand plates develop, then digital rays of future fingers; wrist, elbow start forming)
Umbilical cord formation
between weeks 4 and 8
(amnion expands, forms
tube that encloses the
connecting stalk and a
duct for blood vessels)
FIGURE 7.7 Stages of human development. (b) Embryo at 4 to 6 weeks of development.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Foot plate
Fig. 7-7b, p.160

51. Placenta WEEK 8 WEEK 16 Fig. 7-7c1, p.161
FIGURE 7.7 Stages of human development. (c) Embryo at the transition to the fetal stage of development.
WEEK 8
WEEK 16
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7c1, p.161

52. Final week of embryonic period; embryo looks distinctly human
compared to other
vertebrate embryos
Upper and lower limbs well
formed; fingers and then
toes have separated
Primordial tissues of
all internal, external
structures now developed
FIGURE 7.7 Stages of human development. (c) Embryo at the transition to the fetal stage of development.
Tail has become stubby
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7c2, p.161

53. Length: 16 centimeters (6.4 inches) Weight: 200 grams (7 ounces)
WEEK 16
Length: 16 centimeters (6.4 inches)
Weight: 200 grams (7 ounces)
WEEK 29
Length: 27.5 centimeters (11 inches)
Weight: 1,300 grams (46 ounces)
WEEK 38 (full term)
Length: 50 centimeters (20 inches)
Weight: 3,400 grams (7.5 pounds)
During fetal period, length measurement extends from crown to heel (for embryos, it is the longest measurable dimension, as from crown to rump).
FIGURE 7.7 Stages of human development. (d) Fetus at 16 weeks of development.
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 7-7d, p.161

54. Congenital Malformations
97% of babies are normal at birth
Birth defects can be produced by genetic disorders or exposure to environmental agents
Most are caused by disruptions in embryonic development
Brain and nervous system may be damaged throughout development
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

55. Sources of teratogens
-Teratogens are environmental agents that cause developmental disruptions
Natural in environment
-skunk cabbage contains cyclopamine, which inhibits cholesterol
biosynthesis, preventing a key developmental pathway from working;
Toxoplasma gondii - cat-borne - leads to stillbirths
Human introduced in the environment
-methylmercury, fungicide, central nervous system disorders, cerebral
palsy, mental retardation
Infectious agents
-Rubella (German measles), blindness, hearing loss, heart defects,
mental retardation
Drugs
-Diethylstilbesterol (DES), synthetic estrogen, used to prevent miscarriage
until 1971 (it didn’t work), structural damage to reproductive organs,
increased cancer risk
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

56. Diethylstilbestrol (DES)
-prescribed to ~5 million women
-used to prevent miscarriage and preterm labor
-shown not to be effective in the 1950s, continued to be prescribed
-1970s, women exposed to DES in utero had increased cervical cancer risk,
morphological abnormalities of reproductive tract
-men exposed in utero often had abnormal genitalia
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

57. The Effects of Teratogens
Fig. 7.8
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

58. Fetal Alcohol Syndrome (FAS)
A serious and widespread teratogenic problem
Fetal Alcohol Syndrome – 1.9/1,000 births
Fetal alcohol effect 3.5/1,000 births
Preventable
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

59. Fetal alcohol syndrome
-characterized by small heads, low nose bridge, small brain size, mental retardation
-FAS affects 1 out of newborns in the US
-third most common cause of mental retardation (after Fragile X and Down’s)
FAS
normal
-intellectual and behavioral problems seen even in the absence of morphological
defects
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

60. Alcohol Consumption During Pregnancy Can Result in:
Spontaneous abortion
Growth retardation
Facial abnormalities
Mental retardation
Learning disabilities
Chapter 7 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning