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© 2013 Pearson Education, Inc.
PowerPoint® Lecture Slidesprepared byMeg FlemmingAustin Community College
C H A P T E R
Development and Inheritance
20
© 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.
© 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.
© 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
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Checkpoint (20-1)
1. Define differentiation.
2. What event marks the beginning of
development?
3. Define inheritance.
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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
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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
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Figure 20-1a Fertilization.
A secondary oocyte and numerous sperm at the time of fertilization. Notice the difference in size between the gametes.
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Figure 20-1b Fertilization. Oocyte at Ovulation
Coronaradiata
First polarbody
Zonapellucida
Fertilization and Oocyte Activation
Pronucleus Formation Begins
Nucleus offertilizing
spermatozoon
Femalepronucleus
Cleavage Begins Amphimixis Occurs and Cleavage Begins
Metaphase of firstcleavage division Male
pronucleusFemale
pronucleus
Blastomeres
Spindle Formation andCleavage Preparation
Fertilizingspermatozoon
Second polar body
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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
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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
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Amphimixis (20-2)
• Female pronucleus and male pronucleus fuse
• Moment of conception
• Cell becomes a zygote with 46 chromosomes
• Fertilization is finalized
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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?
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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
© 2013 Pearson Education, Inc.
Checkpoint (20-3)
6. Define gestation.
7. Describe the key features of each trimester.
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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
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Figure 20-2 Cleavage and Blastocyst Formation.
Blastomeres
Polar bodies
2-cell stage4-cell stage
Early morula
Advancedmorula
Hatching
Inner cellmass
Blastocoele
Trophoblast Blastocyst
Days 7–10:Implantation in
uterine wall (See Figure 20-3)
DAY 0:Fertilization
First cleavagedivision
DAY 1 DAY 2DAY 3
DAY 4
DAY 6
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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
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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
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Blastocoele
Lacuna
DAY 6
DAY 7
DAY 8
DAY 9
FUNCTIONAL ZONEOF ENDOMETRIUM
UTERINE CAVITY
Blastocyst
Uterineglands
Trophoblast
Inner cellmass
CellulartrophoblastSyncytial
trophoblast
Amnioticcavity
Developingvilli
Endometrialcapillary
Figure 20-3 Events in Implantation.
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Gastrulation and Germ Layer Formation (20-4)
• By day 12
• Inner cell mass develops into germ layers
• Ectoderm
• Endoderm
• Mesoderm
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Figure 20-4 The Inner Cell Mass and Gastrulation.
Superficial layer
Deep layer
Cellular trophoblast
Amniotic cavity
Yolk sac
Blastocoele
Lacuna
Amnion
Ectoderm
Primitivestreak
Blastodisc
Yolk sac
Mesoderm
Endoderm
Embryonicdisc
Syncytial trophoblast
Day 10: Yolk Sac Formation
Day 12: Gastrulation
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Table 20-1 The Fates of the Germ Layers
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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
© 2013 Pearson Education, Inc.
Figure 20-5 Extraembryonic Membranes and Placenta Formation.Week 2
Week 5
Amnion
Syncytialtrophoblast
Cellulartrophoblast
Mesoderm
Yolk sac
Blastocoele
Chorion
Uterus
Myometrium
Umbilical stalk
Placenta
Yolk sac
Chorionic villiof placenta
Uterine cavity
Amniotic cavity(containingamniotic fluid)
Allantois
Head foldof embryo
ChorionSyncytialtrophoblast
Chorionic villiof placenta
Yolksac
Week 4
Tail fold
Body stalk
Yolk stalk
Yolk sac
Embryonic gut
Embryonichead fold
Umbilical cord
Placenta
Amniotic cavity
Amnion
Chorion
Week 10
Week 3
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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
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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
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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
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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
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Figure 20-6 The Placenta and Placental Circulation.
Chorion
AmnionUmbilical cord (cut) Placenta
Yolk sac
Umbilicalvein
Umbilicalarteries
Chorionicvilli
Area filled withmaternal blood
Maternalblood vessels
Syncytial trophoblastAmnion
Cervix
Vagina
External os
Cervical (mucous)plug in
cervical canal
Uterine cavity
Myometrium
Endometrium
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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
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Future head of embryo
Thickened neural plate(will form brain)
Axis of future spinalcord
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.
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Figure 20-7b Development during the First Trimester.
Medullaoblongata
Ear
Forebrain
Eye
Heart
Bodystalk
Tail
Pharyngealarches
Somites
Arm bud
Leg bud
Week 4. Fiberoptic view of human development at week 4.
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Figure 20-7c Development during the First Trimester.
Chorionicvilli
Amnion
Week 8. Fiberoptic view ofhuman development at week 8.
Umbilicalcord
Placenta
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Amnion
Umbilicalcord
Week 12. Fiberoptic view of humandevelopment at week 12.
Figure 20-7d Development during the First Trimester.
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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?
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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
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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, revealedthrough ultrasound
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Table 20-2 An Overview of Prenatal and Early Postnatal Development* (1 of 4)
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Table 20-2 An Overview of Prenatal and Early Postnatal Development* (2 of 4)
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Table 20-2 An Overview of Prenatal and Early Postnatal Development* (3 of 4)
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Table 20-2 An Overview of Prenatal and Early Postnatal Development* (4 of 4)
© 2013 Pearson Education, Inc.
Figure 20-9 Changes in Body Form and Proportion during Development.
Prenatal DevelopmentEmbryological 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
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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
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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
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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.
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The Three Stages of Labor (20-6)
• Also called parturition
1. Dilation stage
2. Expulsion stage
3. Placental stage
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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"
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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
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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
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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 smoothmuscle cells of the myometrium and make contractionsmore likely. As delivery approaches, the production ofestrogens accelerates. Estrogens also increase thesensitivity of smooth muscle fibers to oxytocin.
Relaxin producedby the placentarelaxes the pelvicarticulations anddilates the cervix.
Growth and theincrease in fetalweight stretchand distort themyometrium.
Fetal pituitaryreleasesoxytocin inresponse toestrogens.
Distortion of the myometrium increasesthe sensitivity of the smooth musclelayers, promoting spontaneous contrac-tions that get stronger and morefrequent as the pregnancy advances.
Labor contractionsmove the fetus andfurther distort themyometrium. Thisdistortion stimulatesadditional oxytocinand prostaglandinrelease. This positivefeedback continuesuntil delivery iscompleted.
Estrogens and oxytocin stimulate the production ofprostaglandins in the endometrium. These localhormones further stimulate smooth muscle contractions.
Maternal oxytocin release isstimulated by high estrogen levelsand by distortion of the cervix.
Oxytocin and prostaglandins both stimulate the myometrium. In addition, the sensitivity of the uterus to oxytocinincreases dramatically; the smooth muscle in a late-term uterus is 100 times more sensitive to oxytocin than thesmooth muscle in a nonpregnant uterus.
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Fully developed fetus before labor begins The Dilation Stage
The Expulsion Stage
Pubicsymphysis
Cervicalcanal
Vagina
Sacralpromontory Cervix
Umbilicalcord
Placenta
The Placental StageUterus Ejection of the
placenta
Figure 20-11 The Stages of Labor.
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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
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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
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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?
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Postnatal Stages (20-7)
• Life stages
• Neonatal period
• Infancy
• Childhood
• Adolescence
• Maturity
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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
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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
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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
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Figure 20-12 The Milk Let-Down Reflex.
Stimulation of hypothalamic nuclei
Posteriorlobe of thepituitarygland
Oxytocin Release
Milk Ejected
Tactile receptorsin nipplesstimulated
Neural impulses arepropagated to thespinal cord.
Start
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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
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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
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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
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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?
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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
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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
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Patterns of Inheritance (20-8)
• Sex chromosomes
• 23rd pair of homologous chromosomes
• Determine genetic male or genetic female
• Karyotype
• Entire set of chromosomes
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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
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Figure 20-13 A Human Karyotype.
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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
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Table 20-3 The Inheritance of Selected Phenotypic Characteristics
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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
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Maternal alleles (contributed bythe ovum). Every ovum will carry
the recessive gene a.
a
Aa
All have normal skinpigmentation
Paternal alleles(contributed bythe spermatozoon).Every sperm pro-duced by a homozy-gous dominant (AA)father will carry the Aallele.
If the father is homozygous for normal pigmentation, all of thechildren will have the genotype Aa, and all will have normalskin pigmentation.
a
Aa
Aa Aa
A
A
Figure 20-14a Predicting Genotypes and Phenotypes with Punnett Squares.
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Maternalalleles
50% of the children are ho-mozygous recessive and
exhibit albinism.
Aa50% 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 isreduced to 50%.
Half of thesperm producedby a heterozygous(Aa) father will carrythe dominant alleleA, and the other half will carry the recessiveallele a.
Figure 20-14b Predicting Genotypes and Phenotypes with Punnett Squares.
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Table 20-4 Fairly Common Inherited Disorders
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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
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Figure 20-15 Inheritance of an X-Linked Trait.
A man has onlyone X chromo-some, so whicheverallele that chromosomecarries determineswhether he has normalcolor vision or is red–green color-blind.
XC XC
Normal female Normal female(carrier)
Color-blindmale
Normal male
XC Y XC Y
XC Xc
XcXC
XC
Y
A woman—who has two Xchromosomes—can be either ho-
mozygous dominant (XCXC) or
heterozygous (XC Xc) and still havenormal color vision. She will beunable to distinguish reds fromgreens only if she carries two
recessive alleles, XcXc.
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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
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Figure 20-16 A Map of Human Chromosomes.
Familial Polyposis of the Colon Abnormal tissue growths that commonly lead to colon cancer
Huntington’s Diseasep. 295
Spinocerebellar AtaxiaDestroys neurons in the brainand spinal cord, resulting inloss of muscle control
Cystic Fibrosis p. 506
Malignant Melanoma p. 125
Multiple Endocrine Neoplasia, Type 2Tumors in endocrine glands and other tissues
Sickle Cell Anemiap. 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 Syndromep. 103
Breast Cancer(one form)p. 658
Familial HypercholesterolemiaExtremely 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 34
5678
910
1112131415
1617181920
2122XY
CHROMOSOMEPAIRS
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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?
© 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?