163 ch 20_lecture_presentation

PowerPoint® Lecture Slidesprepared byMeg FlemmingAustin Community College

C H A P T E R

Development and Inheritance

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.

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.

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

Checkpoint (20-1)

1. Define differentiation.

2. What event marks the beginning of

development?

3. Define inheritance.

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

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

Figure 20-1a Fertilization.

A secondary oocyte and numerous sperm at the time of fertilization. Notice the difference in size between the gametes.

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

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

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

Amphimixis (20-2)

• Female pronucleus and male pronucleus fuse

• Moment of conception

• Cell becomes a zygote with 46 chromosomes

• Fertilization is finalized

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?

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

Checkpoint (20-3)

6. Define gestation.

7. Describe the key features of each trimester.

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

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

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

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

Blastocoele

Lacuna

FUNCTIONAL ZONEOF ENDOMETRIUM

UTERINE CAVITY

Blastocyst

Uterineglands

Trophoblast

Inner cellmass

CellulartrophoblastSyncytial

trophoblast

Amnioticcavity

Developingvilli

Endometrialcapillary

Figure 20-3 Events in Implantation.

Gastrulation and Germ Layer Formation (20-4)

• By day 12

• Inner cell mass develops into germ layers

• Ectoderm

• Endoderm

• Mesoderm

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

Table 20-1 The Fates of the Germ Layers

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

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

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

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

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

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

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

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

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.

Figure 20-7b Development during the First Trimester.

Medullaoblongata

Forebrain

Bodystalk

Pharyngealarches

Somites

Arm bud

Leg bud

Week 4. Fiberoptic view of human development at week 4.

Figure 20-7c Development during the First Trimester.

Chorionicvilli

Amnion

Week 8. Fiberoptic view ofhuman development at week 8.

Umbilicalcord

Placenta

Amnion

Umbilicalcord

Week 12. Fiberoptic view of humandevelopment at week 12.

Figure 20-7d Development during the First Trimester.

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?

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

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

Table 20-2 An Overview of Prenatal and Early Postnatal Development* (1 of 4)

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

1 month 2 years Puberty(between 9–14 years)

18 years

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

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

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.

The Three Stages of Labor (20-6)

• Also called parturition

1. Dilation stage

2. Expulsion stage

3. Placental stage

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"

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

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

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.

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.

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

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

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?

Postnatal Stages (20-7)

• Life stages

• Neonatal period

• Infancy

• Childhood

• Adolescence

• Maturity

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

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

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

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.

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

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

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

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?

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

• Determine unique characteristics of your phenotype

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

• Sex chromosomes

• 23rd pair of homologous chromosomes

• Determine genetic male or genetic female

• Karyotype

• Entire set of chromosomes

• 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

Figure 20-13 A Human Karyotype.

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

Table 20-3 The Inheritance of Selected Phenotypic Characteristics

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

Maternal alleles (contributed bythe ovum). Every ovum will carry

the recessive gene a.

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.

Figure 20-14a Predicting Genotypes and Phenotypes with Punnett Squares.

Maternalalleles

50% of the children are ho-mozygous recessive and

exhibit albinism.

Aa50% of the children are het-erozygous and have normal

pigmentation

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.

Table 20-4 Fairly Common Inherited Disorders

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

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.

Normal female Normal female(carrier)

Color-blindmale

Normal male

XC Y 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.

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

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

1112131415

1617181920

2122XY

CHROMOSOMEPAIRS

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?

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?

163 ch 20_lecture_presentation

pearson education

oocyte oocyte

chromosomes fertilization

oocyte surface

time of fertilization

b fertilization

process of fertilization

paternal chromosomes

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