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Chapter
29
Development
and Inheritance
PowerPoint® Lecture Slides
prepared by Jason LaPres
Lone Star College - North Harris
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Copyright © 2009 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings
Development
 Gradual modification of anatomical
structures and physiological
characteristics from fertilization to
maturity
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Development
 Differentiation
 Creation of different types of cells required in
development
 Occurs through selective changes in genetic activity
 As development proceeds, some genes are turned off, others
are turned on
 Fertilization
 Also called conception
 When development begins
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Development
 Embryological Development
 Occurs during first 2 months after fertilization
 Study of these events is called embryology
 Fetal Development
 Begins at start of ninth week
 Continues until birth
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Development
 Prenatal Development
 Embryological and fetal development stages
 Postnatal Development
 Commences at birth
 Continues to maturity when aging process
begins
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Development
 Inheritance
 Transfer of genetically determined characteristics
from generation to generation
 Genetics
 Study of mechanisms responsible for inheritance
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Fertilization
 Fertilization
 Fusion of two haploid gametes, each
containing 23 chromosomes
 Produces zygote containing 46 chromosomes
Fertilization and the Preparation for Cleavage
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Fertilization
 Spermatozoon
 Delivers paternal chromosomes to
fertilization site
 Travels relatively large distance
 Is small, efficient, and highly streamlined
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Fertilization
 Gamete
 Provides
 Cellular organelles
 Inclusions
 Nourishment
 Genetic programming necessary to support
development of embryo for a week
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Fertilization
 Fertilization
 Occurs in uterine tube within a day after
ovulation
 Secondary oocyte travels a few centimeters
 Spermatozoa must cover distance between
vagina and ampulla
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Fertilization
 Capacitation
 Must occur before spermatozoa can fertilize
secondary oocyte
 Contact with secretions of seminal glands
 Exposure to conditions in female reproductive tract
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Fertilization
 Hyaluronidase
 Enzyme breaks down bonds between adjacent
follicle cells
 Allows spermatozoon to reach oocyte
 Acrosin
 Is a proteolytic enzyme
 Is required to reach oocyte
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Fertilization
 Acrosomal Caps
 Release hyaluronidase and acrosin
 Penetrate corona radiata, zona pellucida, toward
oocyte surface
 Oocyte Activation
 Contact and fusion of cell membranes of sperm and
oocyte
 Follows fertilization
 Oocyte completes meiosis II, becomes mature ovum
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Fertilization
 Polyspermy
 Fertilization by more than one sperm
 Prevented by cortical reaction
 Cortical Reaction
 Releases enzymes that
 Inactivate sperm receptors
 Harden zona pellucida
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Fertilization
 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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Fertilization
 Amphimixis
 Fusion of female pronucleus and male
pronucleus
 Moment of conception
 Cell becomes a zygote with 46 chromosomes
 Fertilization is complete
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Fertilization
 Cleavage
 Series of cell divisions
 Produces daughter cells
 Differentiation
 Involves changes in genetic activity of some cells but
not others
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Fertilization
Figure 29–1a Fertilization: An Oocyte and Numerous Sperm at Time of
Fertilization.
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Fertilization
Figure 29–1b Fertilization and the Preparations for Cleavage.
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Fertilization
Figure 29–1b Fertilization and the Preparations for Cleavage.
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Fertilization
Figure 29–1b Fertilization and the Preparations for Cleavage.
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Fertilization
Figure 29–1b Fertilization and the Preparations for Cleavage.
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Gestation
 Induction
 Cells release chemical substances that affect
differentiation of other embryonic cells
 Can control highly complex processes
 Gestation
 Time spent in prenatal development
 Consists of three integrated trimesters, each 3
months long
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Gestation
 First Trimester
 Period of embryological and early fetal development
 Rudiments of all major organ systems appear
 Second Trimester
 Development of organs and organ systems
 Body shape and proportions change
 By end, fetus looks distinctively human
 Third Trimester
 Rapid fetal growth and deposition of adipose tissue
 Most major organ systems are fully functional
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The First Trimester
 Cleavage
 Sequence of cell divisions begins immediately
after fertilization
 Zygote becomes a pre-embryo, which
develops into multicellular blastocyst
 Ends when blastocyst contacts uterine wall
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The First Trimester
 Implantation
 Begins with attachment of blastocyst to
endometrium of uterus
 Sets stage for formation of vital embryonic
structures
 Placentation
 Occurs as blood vessels form around periphery of
blastocyst and placenta develops
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The First Trimester
 Placenta
 Complex organ permits exchange between maternal and
embryonic circulatory systems
 Supports fetus in second and third trimesters
 Stops functioning and is ejected from uterus after birth
 Embryogenesis
 Formation of viable embryo
 Establishes foundations for all major organ systems
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The First Trimester
 Most dangerous period in prenatal life
 40% of conceptions produce embryos that
survive past first trimester
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The First Trimester
 Blastomeres
 Identical cells produced by cleavage divisions
 Morula
 Stage after 3 days of cleavage
 Pre-embryo is solid ball of cells resembling
mulberry
 Reaches uterus on day 4
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The First Trimester
 Blastocyst
 Formed by blastomeres
 Hollow ball with an inner cavity
 Known as blastocoele
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The First Trimester
 Trophoblast
 Outer layer of cells separate outside world
from blastocoele
 Cells responsible for providing nutrients to
developing embryo
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The First Trimester
 Inner Cell Mass
 Clustered at end of blastocyst
 Exposed to blastocoele
 Insulated from contact with outside
environment by trophoblast
 Will later form embryo
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The First Trimester
Figure 29–2 Cleavage and Blastocyst Formation.
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The First Trimester
 Implantation
 Occurs 7 days after fertilization
 Blastocyst adheres to uterine lining
 Trophoblast cells divide rapidly, creating
several layers
Stage of Implantation
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The First Trimester
 Cellular Trophoblast
 Cells closest to interior of blastocyst
 Syncytial Trophoblast
 Outer layer
 Erodes path through uterine epithelium by
secreting hyaluronidase
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The First Trimester
Figure 29–3 Stages in Implantation.
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The First Trimester
 Ectopic Pregnancy
 Implantation occurs outside of uterus
 Does not produce viable embryo
 Can be life threatening
 Lacunae
 Trophoblastic channels carrying maternal blood
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The First Trimester
 Villi
 Extend away from trophoblast into endometrium
 Increase in size and complexity until day 21
 Amniotic Cavity
 A fluid-filled chamber
 Inner cell mass is organized into an oval sheet two
layers thick
 Superficial layer faces amniotic cavity
 Deeper layer is exposed to fluid contents of blastocoele
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The First Trimester
 Gastrulation
 Formation of third layer of cells
 Cells in specific areas of surface move
toward central line
 Known as primitive streak
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The First Trimester
 Primitive Streak
 Migrating cells leave surface and move between
two layers
 Creates three distinct embryonic layers, or germ
layers
 Ectoderm: consists of the superficial cells that did not
migrate into interior of inner cell mass
 Endoderm: consists of cells that face blastocoele
 Mesoderm: consists of poorly organized layer of
migrating cells between ectoderm and endoderm
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The First Trimester
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The First Trimester
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The First Trimester
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The First Trimester
 Embryonic Disc
 Oval, three-layered sheet
 Produced by gastrulation
 Will form body of embryo
 Rest of blastocyst will be involved in forming
extraembryonic membranes
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The First Trimester
Figure 29–4 The Inner Cell Mass and Gastrulation.
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The First Trimester
 Formation of the Extraembryonic
Membranes
 Support embryological and fetal development
 Yolk sac
 Amnion
 Allantois
 Chorion
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The First Trimester
 Yolk Sac
 Begins as layer of cells spread out around outer edges
of blastocoele to form complete pouch
 Important site of blood cell formation
 Amnion
 Combination of mesoderm and ectoderm
 Ectodermal layer enlarges and cells spread over inner
surface of amniotic cavity
 Mesodermal cells create outer layer
 Continues to enlarge through development
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The First Trimester
 Amniotic Fluid
 Contained in amniotic cavity
 Surrounds and cushions developing embryo or
fetus
 Allantois
 Sac of endoderm and mesoderm
 Base later gives rise to urinary bladder
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The First Trimester
 Chorion
 Combination of mesoderm and trophoblast
 Blood vessels develop within mesoderm
 Rapid-transit system for nutrients that links
embryo with trophoblast
 First step in creation of functional placenta
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The First Trimester
 Chorionic Villi
 In contact with maternal tissues
 Create intricate network within endometrium carrying
maternal blood
 Body Stalk
 Connection between embryo and chorion
 Contains distal portions of allantois and blood vessels
that carry blood to and from placenta
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The First Trimester
 Yolk Stalk
 Narrow connection between endoderm of embryo
and yolk sac
 Decidua Capsularis
 Thin portion of endometrium
 No longer participates in nutrient exchange and
chorionic villi in region disappear
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The First Trimester
Figure 29–5 Extraembryonic Membranes and Placenta Formation.
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The First Trimester
Figure 29–5 Extraembryonic Membranes and Placenta Formation.
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The First Trimester
Figure 29–5 Extraembryonic Membranes and Placenta Formation.
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The First Trimester
 Decidua Basalis
 Disc-shaped area in deepest portion of
endometrium
 Where placental functions are concentrated
 Decidua Parietalis
 Rest of the uterine endometrium
 No contact with chorion
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The First Trimester
 Umbilical Cord
 Connects fetus and placenta
 Contains allantois, placental blood vessels, and
yolk stalk
 Blood Flow to Placenta
 Through paired umbilical arteries
 Returns in single umbilical vein
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The First Trimester
Figure 29–6 A Three-Dimensional View of Placental Structure.
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The First Trimester
Figure 29–6 A Three-Dimensional View of Placental Structure.
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The First Trimester
 The Endocrine Placenta
 Synthesized by syncytial trophoblast, released into
maternal bloodstream
 Human chorionic gonadotropin (hCG)
 Human placental lactogen (hPL)
 Placental prolactin
 Relaxin
 Progesterone
 Estrogens
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The First Trimester
 Human Chorionic Gonadotropin (hCG)
 Appears in maternal bloodstream soon after
implantation
 Provides reliable indication of pregnancy
 Pregnancy ends if absent
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The First Trimester
 Human Chorionic Gonadotropin (hCG)
 Helps prepare mammary glands for milk
production
 Stimulatory effect on other tissues
comparable to growth hormone (GH)
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The First Trimester
 Placental Prolactin
 Helps convert mammary glands to active status
 Relaxin
 A peptide hormone secreted by placenta and corpus
luteum during pregnancy
 Increases flexibility of pubic symphysis, permitting
pelvis to expand during delivery
 Causes dilation of cervix
 Suppresses release of oxytocin by hypothalamus and
delays labor contractions
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The First Trimester
 Embryogenesis
 Body of embryo begins to separate from embryonic
disc
 Body of embryo and internal organs start to form
 Folding, differential growth of embryonic disc produces
bulge that projects into amniotic cavity
 Projections are head fold and tail fold
 Organogenesis
 Process of organ formation
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The First Trimester
Figure 29–7a The First Trimester.
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The First Trimester
Figure 29–7b The First Trimester.
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The First Trimester
Figure 29–7c The First Trimester.
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The First Trimester
Figure 29–7d The First Trimester.
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The Second and Third Trimesters
 Second Trimester
 Fetus grows faster than surrounding placenta
 Third Trimester
 Most of the organ systems become ready
 Growth rate starts to slow
 Largest weight gain
 Fetus and enlarged uterus displace many of mother’s
abdominal organs
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The Second and Third Trimesters
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The Second and Third Trimesters
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The Second and Third Trimesters
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The Second and Third Trimesters
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The Second and Third Trimesters
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The Second and Third Trimesters
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The Second and Third Trimesters
Figure 29–8a The Second and Third Trimesters: A Four-Month-Old
Fetus As Seen through a Fiber-Optic Endoscope.
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The Second and Third Trimesters
Figure 29–8b The Second and Third Trimesters: Head of a Six-MonthOld Fetus As Seen through Ultrasound.
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The Second and Third Trimesters
Figure 29–9a, b Growth of the Uterus and Fetus.
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The Second and Third Trimesters
Figure 29–9c, d Growth of the Uterus and Fetus.
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The Second and Third Trimesters
 Pregnancy and Maternal Systems
 Developing fetus is totally dependent on maternal
organ systems for nourishment, respiration, and waste
removal
 Maternal adaptations include increases in
 Respiratory rate and tidal volume
 Blood volume
 Nutrient and vitamin intake
 Glomerular filtration rate
 Uterus and mammary glands increase in size
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The Second and Third Trimesters
 Progesterone
 Released by placenta
 Has inhibitory effect on uterine smooth muscle
 Prevents extensive, powerful contractions
 Opposition to Progesterone
 Three major factors
 Rising estrogen levels
 Rising oxytocin levels
 Prostaglandin production
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The Second and Third Trimesters
 False Labor
 Occasional spasms in uterine musculature
 Contractions not regular or persistent
 True Labor
 Results from biochemical and mechanical factors
 Continues due to positive feedback
 Labor Contractions
 Begin in myometrium
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The Second and Third Trimesters
 Parturition is forcible expulsion of fetus
 Contractions
 Begin near top of uterus, sweep in wave toward
cervix
 Strong, occur at regular intervals, increase in force
and frequency
 Change position of fetus, move it toward cervical
canal
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The Second and Third Trimesters
Figure 29–10 Factors Involved in the Initiation of Labor and Delivery.
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Labor
 Dilation Stage
 Begins with onset of true labor
 Cervix dilates
 Fetus begins to shift toward cervical canal
 Highly variable in length, but typically lasts over 8 hours
 Frequency of contractions steadily increases
 Amniochorionic membrane ruptures (water breaks)
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Labor
Figure 29–11 The Stages of Labor.
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Labor
 Expulsion Stage
 Begins as cervix completes dilation
 Contractions reach maximum intensity
 Continues until fetus has emerged from vagina
 Typically less than 2 hours
 Delivery
 Arrival of newborn infant into outside world
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Labor
Figure 29–11 The Stages of Labor.
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Labor
 Placental Stage
 Muscle tension builds in walls of partially empty
uterus
 Tears connections between endometrium and
placenta
 Ends within an hour of delivery with ejection of
placenta, or afterbirth
 Accompanied by a loss of blood
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Labor
Figure 29–11 The Stages of Labor.
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Labor
 Episiotomy
 Incision through perineal musculature
 Needed if vaginal canal is too small to pass
fetus
 Repaired with sutures after delivery
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Labor
 Cesarean Section (C-section)
 Removal of infant by incision made through
abdominal wall
 Opens uterus just enough to pass infant’s
head
 Needed if complications arise during dilation
or expulsion stages
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Labor
 Premature Labor
 Occurs when true labor begins before fetus
has completed normal development
 Newborn’s chances of surviving are directly
related to body weight at delivery
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Labor
 Immature Delivery
 Refers to fetuses born at 25–27 weeks of gestation
 Most die despite intensive neonatal care
 Survivors have high risk of developmental
abnormalities
 Premature Delivery
 Refers to birth at 28–36 weeks
 Newborns have a good chance of surviving and
developing normally
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Labor
 Forceps Delivery
 Needed when fetus faces mother’s pubis
instead of sacrum
 Risks to infant and mother are reduced if
forceps are used
 Forceps resemble large, curved salad tongs
 Used to grasp head of fetus
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Labor
 Breech Birth
 Legs or buttocks of fetus enter vaginal canal first
instead of head
 Umbilical cord can become constricted, cutting off
placental blood flow
 Cervix may not dilate enough to pass head
 Prolongs delivery
 Subjects fetus to severe distress and potential injury
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Labor
 Dizygotic Twins
 Also called fraternal twins
 Develop when two separate oocytes were
ovulated and subsequently fertilized
 Genetic makeup not identical
 70% of twins
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Labor
 Monozygotic Twins
 Identical twins
 Result either from
 Separation of blastomeres early in cleavage
 Splitting of inner cell mass before gastrulation
 Genetic makeup is identical because both
formed from same pair of gametes
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Labor
 Conjoined Twins
 Siamese twins
 Genetically identical twins
 Occurs when splitting of blastomeres or of
embryonic disc is not completed
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Labor
 Rates of Multiple Births
 Twins in 1 of every 89 births
 Triplets in 1 of every 892 (7921) births
 Quadruplets in 1 of every 893 (704,969) births
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Postnatal Life

Five Life Stages

Neonatal period

Infancy

Childhood

Adolescence

Maturity
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Postnatal Life
 Neonatal Period: extends from birth to 1 month
 Infancy: 1 month to 2 years of age
 Childhood: 2 years until adolescence
 Adolescence: period of sexual and physical
maturation
 Senescence: process of aging that begins at end
of development (maturity)
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Postnatal Life
 Developmental Stages
 Neonatal period, infancy, childhood, and
adolescence
 Two major events occur
 Organ systems become fully operational
 Individual grows rapidly and body proportions
change significantly
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Postnatal Life
 Pediatrics
 Medical specialty focusing on postnatal
development from infancy to adolescence
 Neonate
 Newborn
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Postnatal Life
 Neonatal Period
 Transition from fetus to neonate
 Systems begin functioning independently
 Respiratory
 Circulatory
 Digestive
 Urinary
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Postnatal Life
 Colostrum
 Secretion from mammary glands
 Ingested by infant during first 2–3 days
 Contains more proteins and less fat than breast milk
 Many proteins are antibodies that help ward off infections
until immune system is functional
 Mucins present inhibit replication of rotaviruses
 As production drops, mammary glands convert to milk
production
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Postnatal Life
 Breast Milk
 Consists of water, proteins, amino acids,
lipids, sugars, and salts
 Also contains large quantities of lysozymes—
enzymes with antibiotic properties
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Postnatal Life
 Milk Let-Down Reflex
 Mammary gland secretion triggered when
infant sucks on nipple
 Continues to function until weaning, typically
1–2 years
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Postnatal Life
Figure 29–12 The Milk Let-Down Reflex.
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Postnatal Life
 Infancy and Childhood
 Growth occurs under direction of circulating
hormones
 Growth hormone
 Suprarenal steroids
 Thyroid hormones
 Growth does not occur uniformly
 Body proportions gradually change
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Postnatal Life
 Puberty is a period of sexual maturation and marks the
beginning of adolescence
 Generally starts at age 12 in boys, age 11 in girls
 Three major hormonal events interact
 Hypothalamus increases production of GnRH
 Circulating levels of FSH and LH rise rapidly
 Ovarian or testicular cells become more sensitive to FSH and LH
 Hormonal changes produce sex-specific differences in
structure and function of many systems
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Postnatal Life
 Adolescence
 Begins at puberty
 Continues until growth is completed
 Maturity (Senescence )
 Aging
 Reduces functional capabilities of individual
 Affects homeostatic mechanisms
 Sex hormone levels decline at menopause or male
climacteric
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Postnatal Life
 Geriatrics
 Medical specialty dealing with problems
associated with aging
 Trained physicians, or geriatricians
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Postnatal Life
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Postnatal Life
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Postnatal Life
Figure 29–13 Growth and Changes in Body Form and Proportion.
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Inheritance
 Nucleated Somatic Cells
 Carry copies of original 46 chromosomes present in
zygote
 Genotype
 Chromosomes and their component genes
 Contain unique instructions that determine anatomical
and physiological characteristics
 Derived from genotypes of parents
 Phenotype
 Physical expression of genotype
 Anatomical and physiological characteristics
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Inheritance
 Homologous Chromosomes
 Members of each pair of chromosomes
 23 pairs carried in every somatic cell
 At amphimixis, one member of each pair is
contributed by spermatozoon, other by ovum
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Inheritance
 Autosomal Chromosomes
 22 pairs of homologous chromosomes
 Most affect somatic characteristics
 Each chromosome in pair has same structure
and carries genes that affect same traits
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Inheritance
 Sex Chromosomes
 Last pair of chromosomes
 Determine whether individual is genetically male or
female
 Karyotype
 Entire set of chromosomes
 Locus
 Gene’s position on chromosome
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Inheritance
Figure 29–14 A Human Karyotype.
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Inheritance
 Alleles are various forms of given gene
 Alternate forms determine precise effect of gene on
phenotype
 Homozygous
 Both homologous chromosomes carry same allele of
particular gene
 Simple Inheritance
 Phenotype determined by interactions between single
pair of alleles
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Inheritance
 Heterozygous
 Homologous chromosomes carry different allele of
particular gene
 Resulting phenotype depends on nature of interaction
between alleles
 Strict Dominance
 Dominant allele expressed in phenotype, regardless
of conflicting instructions carried by other allele
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Inheritance
 Recessive Allele
 Expressed in phenotype only if same allele is present
on both chromosomes of homologous pair
 Incomplete Dominance
 Heterozygous alleles produce unique phenotype
 Codominance
 Exhibits both dominant and recessive phenotypes for
traits
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Inheritance
 Penetrance
 Percentage of individuals with particular genotype that
show “expected” phenotype
 Expressivity
 Extent to which particular allele is expressed
 Teratogens
 Factors that result in abnormal development
 Punnett Square
 Simple box diagram used to predict characteristics of
offspring
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Inheritance
Figure 29–15 Predicting Phenotypic Characters by Using Punnett
Squares.
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Inheritance
 Polygenic Inheritance
 Involves interactions among alleles on several genes
 Cannot predict phenotypic characteristics using
Punnett square
 Linked to risks of developing several important adult
disorders
 Suppression
 One gene suppresses other
 Second gene has no effect on phenotype
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Inheritance
Figure 29–16 The Major Forms of Inheritance.
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Inheritance
 Complementary Gene Action
 Dominant alleles on two genes interact to produce
phenotype different from that seen when one gene
contains recessive alleles
 Sources of Individual Variation
 During meiosis, maternal and paternal chromosomes
are randomly distributed
 Each gamete has unique combination of maternal
and paternal chromosomes
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Inheritance
 Genetic Recombination
 During meiosis, various changes can occur in
chromosome structure, producing gametes with
chromosomes that differ from those of each parent
 Greatly increases range of possible variation among
gametes
 Can complicate tracing of inheritance of genetic
disorders
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Inheritance
 Crossing Over
 Parts of chromosomes become rearranged during
synapsis
 When tetrads form, adjacent chromatids may overlap
 Translocation
 Reshuffling process
 Chromatids may break, overlapping segments trade
places
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Inheritance
Figure 29–17 Crossing Over and Translocation.
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Inheritance
 Genomic Imprinting
 During recombination, portions of
chromosomes may break away and be
deleted
 Effects depend on whether abnormal gamete
is produced through oogenesis or
spermatogenesis
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Inheritance
 Chromosomal Abnormalities
 Damaged, broken, missing, or extra copies of
chromosomes
 Few survive to full term
 Produce variety of serious clinical conditions
 Mutation
 Changes in nucleotide sequence of allele
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Inheritance
 Spontaneous Mutations
 Result of random errors in DNA replication
 Errors relatively common, but in most cases error is
detected and repaired by enzymes in nucleus
 Errors that go undetected and unrepaired have
potential to change phenotype
 Can produce gametes that contain abnormal alleles
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Inheritance
 Carriers
 Individuals who are heterozygous for
abnormal allele but do not show effects of
mutation
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Inheritance
 Sex Chromosomes
 X Chromosome
 Considerably larger
 Have more genes than do Y chromosomes
 Carried by all oocytes
 Y Chromosome
 Includes dominant alleles specifying that the individual will be
male
 Not present in females
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Inheritance
 Sperm
 Carry either X or Y chromosome
 Because males have one of each, can pass
along either
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Inheritance
 X-Linked
 Genes that affect somatic structures
 Carried by X chromosome
 Inheritance does not follow pattern of alleles on
autosomal chromosomes
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Inheritance
Figure 29–18 Inheritance of an X-Linked Trait
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Inheritance
 Human Genome Project
 Goal was to transcribe entire human genome
 Has mapped thousands of human genes
 Genome
 Full complement of genetic material
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Inheritance
 Karyotyping
 Determination of individual’s complete
chromosomal complement
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Inheritance
Figure 29–19 A Map of Human Chromosomes.
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