Download Development and Inheritance

Chapter
20
Development
and Inheritance
PowerPoint® Lecture Slides
prepared by Jason LaPres
Lone Star College - North Harris
Copyright © 2010 Pearson Education, Inc.
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20-1 Development is a
continuous process that
occurs from fertilization
to maturity
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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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20-2 Fertilization — the fusion
of a secondary oocyte and a
spermatozoon — forms
a zygote
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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
• 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
Figure 20-1
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Fertilization
Figure 20-1
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Fertilization
Figure 20-1
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20-3 Gestation consists of
three stages of prenatal
development: the first,
second, and third trimesters
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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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20-4 Cleavage, implantation,
placentation, and
embryogenesis are critical
events of the first
trimester
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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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Cleavage and Blastocyst Formation
• 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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Cleavage and Blastocyst Formation
• Blastocyst
– Formed by blastomeres
– Hollow ball with an inner cavity:
• Known as blastocoele
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Cleavage and Blastocyst Formation
• Trophoblast
– Outer layer of cells separate outside world
from blastocoele
– Cells responsible for providing nutrients to
developing embryo
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Cleavage and Blastocyst Formation
• 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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Cleavage and Blastocyst Formation
Figure 20-2
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Implantation
• 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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Implantation
• Cellular Trophoblast
– Cells closest to interior of blastocyst
• Syncytial Trophoblast
– Outer layer
– Erodes path through uterine epithelium by
secreting hyaluronidase
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Implantation
Figure 20-3
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Implantation
• 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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Implantation
• 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 that is
two layers thick:
• Superficial layer faces amniotic cavity
• Deeper layer is exposed to fluid contents of blastocoele
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Implantation
• 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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Implantation
• 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 the interior of the 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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Implantation
• 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 Inner Cell Mass and Gastrulation
Figure 20-4
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Implantation
• Formation of the Extraembryonic
Membranes
– Support embryological and fetal development:
• Yolk sac
• Amnion
• Allantois
• Chorion
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Implantation
• 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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Implantation
• 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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Implantation
• 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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Placentation
• 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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Placentation
• Yolk Stalk
– Narrow connection between endoderm of embryo
and yolk sac
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Placentation
Figure 20-5
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Placentation
Figure 20-5
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Placentation
Figure 20-5
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Placentation
• 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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Placentation
Figure 20-6
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Placentation
• 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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Placentation
• Human Chorionic Gonadotropin (hCG)
– Appears in maternal bloodstream soon after
implantation
– Provides reliable indication of pregnancy
– Pregnancy ends if absent
– Helps prepare mammary glands for milk
production
– Stimulatory effect on other tissues
comparable to growth hormone (GH)
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Placentation
• 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 20-7a
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The First Trimester
Figure 20-7b
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The First Trimester
Figure 20-7c
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The First Trimester
Figure 20-7d
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20-5 During the second and
third trimesters, maternal
organ systems support the
developing fetus, and the
uterus undergoes structural
and functional changes
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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
Figure 20-8a
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The Second and Third Trimesters
Figure 20-8b
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Changes in Body Form and Proportion
During Development
Figure 20-9
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Effects of Pregnancy on Mother
• 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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Effects of Pregnancy on Mother
• 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
• 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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Factors Involved in the Initiation of
Labor and Delivery
Figure 20-10
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20-6 Labor consists of the
dilation, expulsion, and
placental stages
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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 20-11
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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 20-11
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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 20-11
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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 to 27 weeks of gestation
– Most die despite intensive neonatal care
– Survivors have high risk of developmental
abnormalities
• Premature Delivery
– Refers to birth at 28 to 36 weeks
– Newborns have a good chance of surviving and
developing normally
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Multiple Births
• 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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Multiple Births
• 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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Multiple Births
• Conjoined Twins
– Siamese twins
– Genetically identical twins
– Occurs when splitting of blastomeres or of
embryonic disc is not completed
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Multiple Births
• 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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20-7 Postnatal stages are the
neonatal period, infancy,
childhood, adolescence,
maturity, and senescence
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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 to 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
to 2 years
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Figure 20-12
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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
Figure 20-9
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20-8 Genes and
chromosomes
determine patterns of
inheritance
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Patterns of 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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Patterns of 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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Patterns of 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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Patterns of Inheritance
• Sex Chromosomes
– Last pair of chromosomes
– Determine whether individual is genetically male or
female
• Karyotype
– Entire set of chromosomes
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Chromosomes of a Normal Male
Figure 20-13
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Patterns of Inheritance
• Alleles are various forms of a given gene
– Alternate forms determine precise effect of gene on
phenotype
• Homozygous
– Both homologous chromosomes carry same allele of a
particular gene
• Simple Inheritance
– Phenotype determined by interactions between single
pair of alleles
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Patterns of Inheritance
• Heterozygous
– Homologous chromosomes carry different allele of a
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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Patterns of Inheritance
• Recessive Allele
– Expressed in phenotype only if same allele is present on both
chromosomes of homologous pair
• Codominance
– Exhibits both dominant and recessive phenotypes for traits
• Punnett Square
– Simple box diagram used to predict characteristics of offspring
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Predicting Genotypes and Phenotypes
Figure 20-14 a,b
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Patterns of 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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Patterns of Inheritance
• Carriers
– Individuals who are heterozygous for
abnormal allele but do not show effects of
mutation
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Patterns of Inheritance
• Sex Chromosomes
– X Chromosome:
• Considerably larger
• Has more genes than does Y chromosome
• Carried by all oocytes
– Y Chromosome:
• Includes dominant alleles specifying that the individual will be
male
• Not present in females
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Patterns of Inheritance
• Sperm
– Carry either X or Y chromosome
– Because males have one of each, can pass
along either
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Patterns of 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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The Human Genome Project and
Beyond
• 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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The Human Genome Project and
Beyond
• Karyotyping
– Determination of individual’s complete
chromosomal complement
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Figure 20-15
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