The document outlines key topics in human development and inheritance covered in Chapter 20, including: 1. The three stages of prenatal development - embryological, fetal, and prenatal - and the major events of each stage such as organogenesis in the first trimester. 2. The process of fertilization and how it produces a zygote with 46 chromosomes through the fusion of a sperm and egg. 3. The formation and importance of the placenta as an endocrine organ that secretes hormones to maintain the corpus luteum and pregnancy. 4. The three stages of labor - dilation, expulsion, and placental - and events that occur in each like amniotic rupture and

1. © 2013 Pearson Education, Inc.
PowerPoint®
Lecture Slides
prepared by
Meg Flemming
Austin Community College
C H A P T E R
Development
and Inheritance
20

2. © 2013 Pearson Education, Inc.
Chapter 20 Learning Outcomes
• 20-1
• Explain the relationship between differentiation and development,
and describe the various stages of development.
• 20-2
• Describe the process of fertilization.
• 20-3
• List the three stages of prenatal development, and describe the
major events of each.
• 20-4
• Explain how the three germ layers participate in the formation of
extraembryonic membranes, and discuss the importance of the
placenta as an endocrine organ.

3. © 2013 Pearson Education, Inc.
Chapter 20 Learning Outcomes
• 20-5
• Describe the interplay between maternal organ systems and the
developing fetus, and discuss the structural and functional changes
in the uterus during gestation.
• 20-6
• List and discuss the events that occur during labor and delivery.
• 20-7
• Identify the features and physiological changes of the postnatal
stages of life.
• 20-8
• Relate the basic principles of genetics to the inheritance of human
traits.

4. © 2013 Pearson Education, Inc.
Basics of Development (20-1)
• Differentiation is formation of different cell types
• Fertilization (or conception) is fusing of gametes
• Embryological development is first two months
• Fetal development is from the ninth week until birth
• Prenatal is both embryological and fetal development
• Postnatal continues to maturity
• Genetics is the study of mechanisms of inheritance

5. © 2013 Pearson Education, Inc.
Checkpoint (20-1)
1. Define differentiation.
2. What event marks the beginning of
development?
3. Define inheritance.

6. © 2013 Pearson Education, Inc.
Fertilization (20-2)
• Fusion of two haploid gametes each with 23
chromosomes
• Produces a zygote with 46 chromosomes
• Sperm provides paternal chromosomes
• Oocyte provides maternal chromosomes,
organelles, and nourishment to support embryo
• Occurs in upper third of uterine tube

7. © 2013 Pearson Education, Inc.
Fertilization (20-2)
• Sperm are motile when deposited in vagina
• Then must be exposed to peg cells in wall of uterine tube to
complete capacitation
• Requires dozens of sperm to reach oocyte
• Takes more than one to break through corona radiata around
oocyte

8. © 2013 Pearson Education, Inc.
Figure 20-1a Fertilization.
A secondary oocyte and
numerous sperm at the time
of fertilization. Notice the
difference in size between
the gametes.

9. © 2013 Pearson Education, Inc.
Figure 20-1b Fertilization. Oocyte at Ovulation
Corona
radiata
First polar
body
Zona
pellucida
Fertilization and Oocyte
Activation
Pronucleus Formation
Begins
Nucleus of
fertilizing
spermatozoon
Female
pronucleus
Cleavage Begins Amphimixis Occurs
and Cleavage Begins
Metaphase of first
cleavage division Male
pronucleus
Female
pronucleus
Blastomeres
Spindle Formation and
Cleavage Preparation
Fertilizing
spermatozoon
Second
polar body

10. © 2013 Pearson Education, Inc.
Ovulation (20-2)
• Results in expulsion of an immature secondary
oocyte
• Acrosomal caps of spermatozoa
• Release hyaluronidase
• Penetrate corona radiata, zona pellucida, toward oocyte
surface

11. © 2013 Pearson Education, Inc.
Oocyte Activation (20-2)
• Contact and fusion of cell membranes of sperm
and oocyte
• Oocyte undergoes last stages of meiosis II
• Female pronucleus
• Nuclear material remaining in ovum after oocyte activation
• Male pronucleus
• Swollen nucleus of spermatozoon
• Migrates to center of cell

12. © 2013 Pearson Education, Inc.
Amphimixis (20-2)
• Female pronucleus and male pronucleus fuse
• Moment of conception
• Cell becomes a zygote with 46 chromosomes
• Fertilization is finalized

13. © 2013 Pearson Education, Inc.
Checkpoint (20-2)
4. What two important roles do the acrosomal
enzymes of spermatozoa play in fertilization?
5. How many chromosomes are contained within a
human zygote?

14. © 2013 Pearson Education, Inc.
The Three Stages of Gestation (20-3)
• Also called pregnancy
• First trimester
• Embryological and early fetal development
• Basic components of organ systems appear
• Second trimester
• Organs and organ systems near completion of
development
• Third trimester
• Rapid fetal growth
• Organ systems become fully functional

15. © 2013 Pearson Education, Inc.
Checkpoint (20-3)
6. Define gestation.
7. Describe the key features of each trimester.

16. © 2013 Pearson Education, Inc.
Cleavage and Blastocyte Formation (20-4)
• Cleavage is a sequence of cell divisions
• Begins immediately after fertilization
• Daughter cells become smaller blastomeres
• Zygote becomes a pre-embryo, a morula
• Develops into multicellular blastocyst
• Outer layer is trophoblast; inner cell mass is to one side
• Ends when blastocyst contacts uterine wall

17. © 2013 Pearson Education, Inc.
Figure 20-2 Cleavage and Blastocyst Formation.
Blastomeres
Polar bodies
2-cell stage
4-cell stage
Early morula
Advanced
morula
Hatching
Inner cell
mass
Blastocoele
Trophoblast Blastocyst
Days 7–10:
Implantation in
uterine wall
(See Figure 20-3)
DAY 0:
Fertilization
First cleavage
division
DAY 1 DAY 2
DAY 3
DAY 4
DAY 6

18. © 2013 Pearson Education, Inc.
Implantation (20-4)
• Begins as blastocyst adheres to endometrium of
uterus
• Occurs in day 6–9
• Inner cell mass develops into syncytial trophoblast
• Sets stage for formation of vital embryonic structures
• Ectopic pregnancy
• Implantation occurs in site other than uterus

19. © 2013 Pearson Education, Inc.
Formation of the Amniotic Cavity (20-4)
• Fluid-filled cavity
• Inner cell mass separates from trophoblast
• Cavity develops by day 9
• Yolk sac forms by day 10

20. © 2013 Pearson Education, Inc.
Blastocoele
Lacuna
DAY 6
DAY 7
DAY 8
DAY 9
FUNCTIONAL ZONE
OF ENDOMETRIUM
UTERINE CAVITY
Blastocyst
Uterine
glands
Trophoblast
Inner cell
mass
Cellular
trophoblastSyncytial
trophoblast
Amniotic
cavity
Developing
villi
Endometrial
capillary
Figure 20-3 Events in Implantation.

21. © 2013 Pearson Education, Inc.
Gastrulation and Germ Layer Formation (20-4)
• By day 12
• Inner cell mass develops into germ layers
• Ectoderm
• Endoderm
• Mesoderm

22. © 2013 Pearson Education, Inc.
Figure 20-4 The Inner Cell Mass and Gastrulation.
Superficial layer
Deep layer
Cellular trophoblast
Amniotic cavity
Yolk sac
Blastocoele
Lacuna
Amnion
Ectoderm
Primitive
streak
Blastodisc
Yolk sac
Mesoderm
Endoderm
Embryonic
disc
Syncytial trophoblast
Day 10: Yolk Sac Formation
Day 12: Gastrulation

23. © 2013 Pearson Education, Inc.
Table 20-1 The Fates of the Germ Layers

24. © 2013 Pearson Education, Inc.
Four Extraembryonic Membranes (20-4)
1. Yolk sac
• Site of early nutrients and blood cell formation
2. Amnion
• Contains amnionic fluid
3. Allantois
• Gives rise to urinary bladder
4. Chorion
• Provides rapid transit pathway for nutrients to embryo

25. © 2013 Pearson Education, Inc.
Figure 20-5 Extraembryonic Membranes and Placenta Formation.
Week 2
Week 5
Amnion
Syncytial
trophoblast
Cellular
trophoblast
Mesoderm
Yolk sac
Blastocoele
Chorion
Uterus
Myometrium
Umbilical stalk
Placenta
Yolk sac
Chorionic villi
of placenta
Uterine cavity
Amniotic cavity
(containing
amniotic fluid)
Allantois
Head fold
of embryo
Chorion
Syncytial
trophoblast
Chorionic villi
of placenta
Yolk
sac
Week 4
Tail fold
Body stalk
Yolk stalk
Yolk sac
Embryonic gut
Embryonic
head fold
Umbilical cord
Placenta
Amniotic cavity
Amnion
Chorion
Week 10
Week 3

26. © 2013 Pearson Education, Inc.
Placentation (20-4)
• Occurs as blood vessels form in chorion around
periphery of blastocyst
• Chorionic villi form in contact with maternal tissue
• By week 4 embryo, amnion, and yolk sac are
within fluid-filled chamber
• By week 10 fetus floats in amniotic cavity
• Connected by umbilical cord

27. © 2013 Pearson Education, Inc.
Placental Circulation (20-4)
• By end of the first trimester circulation is
developed
• Umbilical arteries
• Take deoxygenated blood to placenta
• Umbilical vein
• Returns oxygenated blood from placenta to fetus

28. © 2013 Pearson Education, Inc.
First Trimester Endocrine Secretions of the
Placenta (20-4)
• Human chorionic gonadotropin (hCG)
• Maintains corpus luteum
• Results in maintenance of endometrial lining
• Presence in urine used as indicator of pregnancy
• Progesterone and estrogens
• Secreted by corpus luteum until placenta takes over
• Prevents menses

29. © 2013 Pearson Education, Inc.
Third Trimester Endocrine Secretions of
Placenta (20-4)
• Human placental lactogen and placental
prolactin
• Rise at end of third trimester
• Prepare mammary glands for milk production
• Relaxin
• Increases flexibility of pubis symphysis
• Causes dilation of cervix
• Suppresses secretion of oxytocin, delaying onset of labor
contractions

30. © 2013 Pearson Education, Inc.
Figure 20-6 The Placenta and Placental Circulation.
Chorion
Amnion
Umbilical cord (cut) Placenta
Yolk sac
Umbilical
vein
Umbilical
arteries
Chorionic
villi
Area filled with
maternal blood
Maternal
blood vessels
Syncytial trophoblast
Amnion
Cervix
Vagina
External os
Cervical (mucous)
plug in
cervical canal
Uterine cavity
Myometrium
Endometrium

31. © 2013 Pearson Education, Inc.
Embryogenesis (20-4)
• Formation of viable embryo
• Folding and differential growth
• By week 4 dorsal and ventral surfaces are
apparent
• Organogenesis
• Organ formation in first trimester

32. © 2013 Pearson Education, Inc.
Future head of embryo
Thickened neural plate
(will form brain)
Axis of future spinal
cord
Somites
Neural folds
Cut wall of amniotic
cavity
Future tail of embryo.
Week 2. An SEM of the superior surface of a
monkey embryo at 2 weeks of development. A
human embryo at this stage would look essentially
the same.
Figure 20-7a Development during the First Trimester.

33. © 2013 Pearson Education, Inc.
Figure 20-7b Development during the First Trimester.
Medulla
oblongata
Ear
Forebrain
Eye
Heart
Body
stalk
Tail
Pharyngeal
arches
Somites
Arm bud
Leg bud
Week 4. Fiberoptic view of human development
at week 4.

34. © 2013 Pearson Education, Inc.
Figure 20-7c Development during the First Trimester.
Chorionic
villi
Amnion
Week 8. Fiberoptic view of
human development at week 8.
Umbilical
cord
Placenta

35. © 2013 Pearson Education, Inc.
Amnion
Umbilical
cord
Week 12. Fiberoptic view of human
development at week 12.
Figure 20-7d Development during the First Trimester.

36. © 2013 Pearson Education, Inc.
Checkpoint (20-4)
8. What is the developmental fate of the inner cell
mass of the blastocyst?
9. Sue's pregnancy test indicates elevated levels of
the hormone hCG (human chorionic
gonadotropin). Is she pregnant?
10. What are two important functions of the
placenta?

37. © 2013 Pearson Education, Inc.
Second and Third Trimester Development
(20-5)
• Second trimester
• Fetus grows faster than placenta
• Third trimester
• Basic components of organ systems appear
• Most are ready to perform functions
• Largest fetal weight gain occurs

38. © 2013 Pearson Education, Inc.
Figure 20-8 The Fetus during the Second and Third Trimesters.
A four-month-old fetus, seen through a fiberoptic endoscope Head of a six-month-old fetus, revealed
through ultrasound

39. © 2013 Pearson Education, Inc.
Table 20-2 An Overview of Prenatal and Early Postnatal Development* (1 of 4)

40. © 2013 Pearson Education, Inc.
Table 20-2 An Overview of Prenatal and Early Postnatal Development* (2 of 4)

41. © 2013 Pearson Education, Inc.
Table 20-2 An Overview of Prenatal and Early Postnatal Development* (3 of 4)

42. © 2013 Pearson Education, Inc.
Table 20-2 An Overview of Prenatal and Early Postnatal Development* (4 of 4)

43. © 2013 Pearson Education, Inc.
Figure 20-9 Changes in Body Form and Proportion during Development.
Prenatal Development
Embryological Development
4 weeks
8 weeks
Fetal Development
16 weeks
Postnatal Development
Neonatal Infancy Childhood Adolescence Maturity
5 ft
4 ft
3 ft
2 ft
1 ft
0
1 month 2 years Puberty
(between 9–14 years)
18 years

44. © 2013 Pearson Education, Inc.
Changes in Maternal Systems (20-5)
• Respiratory rate and tidal volume increase
• Blood volume increases
• Nutrient requirements increase
• GFR increases
• Uterus increases in size
• Mammary glands increase in size and activity

45. © 2013 Pearson Education, Inc.
Structural and Functional Uterine Changes
(20-5)
• At end of gestation the uterus:
• Has grown from 3 to 12 inches in length
• Contains 2 liters of fluid, fetus, and placenta
• Labor contractions
• Fetal oxytocin triggers positive feedback mechanism
• Increases myometrial contractions

46. © 2013 Pearson Education, Inc.
Checkpoint (20-5)
11. List the major changes that occur in maternal
systems during pregnancy.
12. Why does a woman's blood volume increase
during pregnancy?
13. By what means does the uterus greatly increase
in size and weight during pregnancy?
14. Identify three major factors opposing the
calming action of progesterone on the uterus.

47. © 2013 Pearson Education, Inc.
The Three Stages of Labor (20-6)
• Also called parturition
1. Dilation stage
2. Expulsion stage
3. Placental stage

48. © 2013 Pearson Education, Inc.
The Dilation Stage (20-6)
• Fetus shifts toward cervix
• This stage is highly variable in length, but typically
lasts 8 or more hours
• Amnion ruptures, "water breaks"

49. © 2013 Pearson Education, Inc.
The Expulsion Stage (20-6)
• Fetus pushed through cervix and vagina
• Referred to as delivery
• Episiotomy
• Incision in perineal musculature to enlarge birth canal
• Cesarean section
• Incision in abdominal wall to deliver fetus if vaginal delivery
not possible

50. © 2013 Pearson Education, Inc.
The Placental Stage (20-6)
• Uterine contractions tear connections between
endometrium and placenta
• Placenta is ejected from body as "afterbirth"
• Retained placenta can result in infection

51. © 2013 Pearson Education, Inc.
Figure 20-10 Factors Involved in Initiating and Sustaining Labor and Delivery.
Placental Factors Fetal Factors
Distortion of Myometrium
Prostaglandin ProductionMaternal Oxytocin Release
Increased Excitability of the Myometrium
LABOR CONTRACTIONS OCCUR
Placental estrogens increase the sensitivity of the smooth
muscle cells of the myometrium and make contractions
more likely. As delivery approaches, the production of
estrogens accelerates. Estrogens also increase the
sensitivity of smooth muscle fibers to oxytocin.
Relaxin produced
by the placenta
relaxes the pelvic
articulations and
dilates the cervix.
Growth and the
increase in fetal
weight stretch
and distort the
myometrium.
Fetal pituitary
releases
oxytocin in
response to
estrogens.
Distortion of the myometrium increases
the sensitivity of the smooth muscle
layers, promoting spontaneous contrac-
tions that get stronger and more
frequent as the pregnancy advances.
Labor contractions
move the fetus and
further distort the
myometrium. This
distortion stimulates
additional oxytocin
and prostaglandin
release. This positive
feedback continues
until delivery is
completed.
Estrogens and oxytocin stimulate the production of
prostaglandins in the endometrium. These local
hormones further stimulate smooth muscle contractions.
Maternal oxytocin release is
stimulated by high estrogen levels
and by distortion of the cervix.
Oxytocin and prostaglandins both stimulate the myometrium. In addition, the sensitivity of the uterus to oxytocin
increases dramatically; the smooth muscle in a late-term uterus is 100 times more sensitive to oxytocin than the
smooth muscle in a nonpregnant uterus.

52. © 2013 Pearson Education, Inc.
Fully developed fetus before labor begins The Dilation Stage
The Expulsion Stage
Pubic
symphysis
Cervical
canal
Vagina
Sacral
promontory Cervix
Umbilical
cord
Placenta
The Placental Stage
Uterus Ejection of the
placenta
Figure 20-11 The Stages of Labor.

53. © 2013 Pearson Education, Inc.
Premature Labor (20-6)
• Contractions occur before fetus completes development
• Miscarriage or spontaneous abortion
• Prior to end of second trimester, fetal weight under 500 g
• Immature delivery
• Fetal weight above 500 g
• Most born at 25–27 weeks of gestation die or have complications
• Premature delivery
• Birth at 28–36 weeks requires extra care, infants usually survive

54. © 2013 Pearson Education, Inc.
Multiple Births (20-6)
• "Fraternal" or dizygotic
• Two separate oocytes are fertilized at same time
• "Identical" or monozygotic
• Blastomeres separate early in cleavage
• Conjoined twins
• When splitting of blastomeres is incomplete
• Shared skin and organs

55. © 2013 Pearson Education, Inc.
Checkpoint (20-6)
15. Name the three stages of labor.
16. What is the difference between immature
delivery and premature delivery?
17. What are the biological terms for fraternal twins
and identical twins?

56. © 2013 Pearson Education, Inc.
Postnatal Stages (20-7)
• Life stages
• Neonatal period
• Infancy
• Childhood
• Adolescence
• Maturity

57. © 2013 Pearson Education, Inc.
The Neonatal Period (20-7)
• Newborn is also called a neonate
1. Filling collapsed lungs with powerful inhalation
2. Changes in blood pressure and flow rates
• Triggers separation of systemic and pulmonary circuits
3. Heart rate slows from 150 bpm to 120–140 bpm
4. Digestive system becomes active with nursing

58. © 2013 Pearson Education, Inc.
The Neonatal Period (20-7)
5. Kidneys eliminate urine
• Lack ability to concentrate urine
• Neonates require high fluid intake
6. Mechanisms for controlling body temperature
• Develops subcutaneous fat layer
• Increases metabolic activity

59. © 2013 Pearson Education, Inc.
Lactation and the Mammary Glands (20-7)
• By month 6 of gestation, mammary glands fully
developed
• Colostrum
• Early secretion includes:
• Higher proteins, lower fat than breast milk
• Proteins are mostly antibodies for short-term immunity
• Milk let-down reflex
• Initiated by suckling
• Functions until weaning

60. © 2013 Pearson Education, Inc.
Figure 20-12 The Milk Let-Down Reflex.
Stimulation of hypothalamic nuclei
Posterior
lobe of the
pituitary
gland
Oxytocin Release
Milk Ejected
Tactile receptors
in nipples
stimulated
Neural impulses are
propagated to the
spinal cord.
Start

61. © 2013 Pearson Education, Inc.
Infancy and Childhood (20-7)
• Growth
• Directed by circulating hormones
• GH, adrenal steroids, TH
• Specific effects
• Are unique from organ to organ
• Results in nonuniformity of growth patterns

62. © 2013 Pearson Education, Inc.
Adolescence (20-7)
• Begins at onset of puberty
• Increase in GnRH
• Increase in LH and FSH
• Gamete formation
• Secretion of sex hormones
• Development of secondary sex characteristics
• Rapid growth spurt

63. © 2013 Pearson Education, Inc.
Maturity (20-7)
• Often identified as starting when growth stops
• Physiological changes continue
• Menopause and male climacteric
• Senescence
• The aging process
• Ultimately leads to death

64. © 2013 Pearson Education, Inc.
Checkpoint (20-7)
18. Name the postnatal stages of development.
19. What is the difference between colostrum and
breast milk?
20. Increases in the blood levels of GnRH, FSH, LH,
and sex hormones mark the onset of which
stage of development?

65. © 2013 Pearson Education, Inc.
Genes and Chromosomes (20-8)
• DNA
• Contains chromosomes, which contain genes
• Segments of DNA with peptide synthesis information
• Genotype
• Original 46 chromosomes formed in zygote retained in every
cell
• Determine unique characteristics of your phenotype

66. © 2013 Pearson Education, Inc.
Patterns of Inheritance (20-8)
• Homologous chromosomes
• Members of each pair of chromosomes
• One member contributed by sperm, other by ovum
• Autosomal chromosomes
• 22 pairs of homologous chromosomes
• Affect somatic characteristics like hair color

67. © 2013 Pearson Education, Inc.
Patterns of Inheritance (20-8)
• Sex chromosomes
• 23rd pair of homologous chromosomes
• Determine genetic male or genetic female
• Karyotype
• Entire set of chromosomes

68. © 2013 Pearson Education, Inc.
Patterns of Inheritance (20-8)
• Alleles are forms of a particular gene
• Homozygous
• When both alleles are the same for a specific trait
• Heterozygous
• Alleles are not identical
• Dominant will be expressed phenotypically
• Recessive will not be expressed unless on both
chromosomes of pair

69. © 2013 Pearson Education, Inc.
Figure 20-13 A Human Karyotype.

70. © 2013 Pearson Education, Inc.
Predicting Inheritance (20-8)
• Simple inheritance
• Phenotypes determined by interactions of single pair of
alleles
• Fairly easy to predict
• Polygenic inheritance
• Phenotypes determined by interaction of multiple alleles
• Difficult to predict

71. © 2013 Pearson Education, Inc.
Table 20-3 The Inheritance of Selected Phenotypic Characteristics

72. © 2013 Pearson Education, Inc.
Predicting Inheritance (20-8)
• Genotype for specific trait indicated by letters
• Dominant trait uses capital letter
• Recessive trait uses lowercase letter
• Example: AA is homozygous dominant, Aa is heterozygous,
aa is homozygous recessive
• Combinations of parental alleles determine outcome
• Can be predicted using Punnett square

73. © 2013 Pearson Education, Inc.
Maternal alleles (contributed by
the ovum). Every ovum will carry
the recessive gene a.
a
Aa
All have normal skin
pigmentation
Paternal alleles
(contributed by
the spermatozoon).
Every sperm pro-
duced by a homozy-
gous dominant (AA)
father will carry the A
allele.
If the father is homozygous for normal pigmentation, all of the
children will have the genotype Aa, and all will have normal
skin pigmentation.
a
Aa
Aa Aa
A
A
Figure 20-14a Predicting Genotypes and Phenotypes with Punnett Squares.

74. © 2013 Pearson Education, Inc.
Maternal
alleles
50% of the children are ho-
mozygous recessive and
exhibit albinism.
Aa
50% of the children are het-
erozygous and have normal
pigmentation
a a
Aa
aa aa
A
a
If the father is heterozygous for normal skin pigmentation,
the probability that a child will have normal pigmentation is
reduced to 50%.
Half of the
sperm produced
by a heterozygous
(Aa) father will carry
the dominant allele
A, and the other half
will carry the recessive
allele a.
Figure 20-14b Predicting Genotypes and Phenotypes with Punnett Squares.

75. © 2013 Pearson Education, Inc.
Table 20-4 Fairly Common Inherited Disorders

76. © 2013 Pearson Education, Inc.
Sex-Linked Inheritance (20-8)
• X chromosome
• Larger with more genes
• Carried by all oocytes
• Y chromosome
• Includes dominant alleles for male genotype
• X-linked traits
• Alleles for somatic traits on the X chromosome

77. © 2013 Pearson Education, Inc.
Figure 20-15 Inheritance of an X-Linked Trait.
A man has only
one X chromo-
some, so whichever
allele that chromosome
carries determines
whether he has normal
color vision or is red–
green color-blind.
XC
XC
Normal female Normal female
(carrier)
Color-blind
male
Normal male
XC
Y XC
Y
XC
Xc
Xc
XC
XC
Y
A woman—who has two X
chromosomes—can be either ho-
mozygous dominant (XC
XC
) or
heterozygous (XC
Xc
) and still have
normal color vision. She will be
unable to distinguish reds from
greens only if she carries two
recessive alleles, Xc
Xc
.

78. © 2013 Pearson Education, Inc.
Human Genome Project (20-8)
• Genome is the full set of DNA in chromosomes
mapped through karyotyping
• All human chromosomes have been sequenced
• Total number of genes estimated at 20,000–25,000
• 99 percent of all nucleotide bases same in all people
• Single nucleotide polymorphisms locate disease
sequences on chromosomes
• 10,000 single-gene disorders have been described

79. © 2013 Pearson Education, Inc.
Figure 20-16 A Map of Human Chromosomes.
Familial Polyposis of the Colon
Abnormal tissue growths that
commonly lead to colon cancer
Huntington’s Disease
p. 295
Spinocerebellar Ataxia
Destroys neurons in the brain
and spinal cord, resulting in
loss of muscle control
Cystic Fibrosis
p. 506
Malignant Melanoma
p. 125
Multiple Endocrine Neoplasia, Type 2
Tumors in endocrine glands and
other tissues
Sickle Cell Anemia
p. 385
PKU
(phenylketonuria)
p. 587
Retinoblastoma
A relatively common tumor of the eye,
accounting for 2% of childhood malignancies
Alzheimer’s Disease
(one form) p. 294
Marfan Syndrome
p. 103
Breast Cancer
(one form)
p. 658
Familial Hypercholesterolemia
Extremely high cholesterol
Down Syndrome
p. 700
Hemophilia
p. 399
Muscular Dystrophy
p. 236
Color Blindness (multiple forms)
p. 324
Prostate Cancer
p. 667
1 2 3
4
5
6
7
8
9
10
11121314
15
16
17
18
19
20
21
22XY
CHROMOSOME
PAIRS

80. © 2013 Pearson Education, Inc.
Checkpoint (20-8)
21. Describe the relationship between genotype and
phenotype.
22. Curly hair is an autosomal dominant trait. What
would be the phenotype of a person who is
heterozygous for this trait?
23. Joe has three daughters and complains that it's
his wife's "fault" that he has no sons. What
would you tell him?

81. © 2013 Pearson Education, Inc.
Checkpoint (20-8)
24. The human genome consists of approximately
3200 Mb. What is a genome, and how many
nucleotide base pairs does 3200 Mb represent?