The humanbody contains100 trillioncells.

There is anucleus insideeach humancell (except redblood cells).

Each nucleuscontains 46chromosomes,arranged in 23 pairs.

Onechromosomeof every pair isfrom eachparent.

Thechromosomesare filled withtightly coiledstrands ofDNA.

Genes are segmentsof DNA that containinstructions to makeproteins— thebuilding blocksof life.

Gametes and Zygote

Sperm

Ovum

Gametes(reproductive cells)

Fertilization Zygote

Sperm

Cell with 46 chromosomes (only one pair of homologouschromosomes is shown here). Each member of the pair has begun to replicate similar tomitotic cell division.

First meiotic cell divisionbegins, but does not proceedas in mitosis. Instead of thereplicated chromosome splitting apart, one member of eachhomologous pair becomes a part of the first-generation daughter cell.

The second meiotic division proceeds after the first is completed;now the replicated chromosomeacquired in the first-generationdaughter cell splits apart.

Each of the four gametesproduced by the two-step processnow has acquired one memberof the pair of homologouschromosomes.

The Process of Meiosis for Sperm Cells

Cell nucleus with a pair of chromosomes

Chromosomes split and replicate to producetwo identical pairs

The pairs separate, and the cell divides

Each daughter cell now has a pair of chromosomes that is identical to the original pair

The Process of Mitosis

GENOTYPE AND PHENOTYPE

GENOTYPE: Set of genetic traits a person inherits; a person’s inborn capacity or potential

PHENOTYPE: Set of traits a person actually displays, resulting from a combination of the person’s genotype (potential) and life experiences that modify that potential

X

X X

Y

NormalFather

Carrier Mother

XX

Normal

Daughter

(25%)

XX

Carrier

Daughter

(25%)

XY

Normal

Son

(25%)

XY

Hemophilic

Son

(25%)

Inheritance of Hemophilia, a Sex-Linked Disorder

FR

EQ

UE

NC

Y O

F D

OW

N S

YN

DR

OM

E (

PE

R 1

000)

MATERNAL AGE (YEARS)

15 20 25 30 35 40 45 50

100

90

80

70

60

50

40

30

20

10

0

Relationship Between Maternal Age and the Incidence of Down Syndrome

r

D r

rNormalFather

Affected Parent(Has the Disorder)

DrAffected

(25%)

rrnormal(25%)

DrAffected

(25%)

rrnormal(25%)

Inheritance of a Dominant Gene Disorder

(50%) (50%)

Inheritance of a Recessive Gene Disorder

D

r

CarrierFather

Carrier Mother

DrAffected

(25%)

rrnormal(25%)

DrAffected

(25%)

rrnormal(25%)

D r

Risk of Selected Genetic Disorders

ChromosomalDown SyndromeKlinefelter syndrome (XXY)Fragile X syndrome

Turner syndrome (XO)

Dominant GenePolydactylyAchondroplasiaHuntington disease

Recessive GeneCystic fibrosisSickle-cell diseaseTay-Sachs disease

X LinkedHemophilia

MultifactorialCongenital heart diseaseNeural tube defectCleft lip/cleft palate

Sources: ACOG (1990); Blatt (1988); Diamond (1989(; Hagerman (1996); Selekman (1993); Stratford (1994).

1/8001/800 men1/1,200 male births1/2,000 female births1/3,00 women

1/300 - 1/1001/2,3001/15,000 - 1/5,000

1/2,500 white persons (risk of being a carrier is 1/25)1/625 African Americans (risk of being a carrier is 1/10)1/3,600 Eastern European Jews(risk of being a carrier is 1/30 -

1/300)

1/2,500 male babies

1/1251 - 2/1,0001/1,000 - 1/5,000

Who Should Seek Prenatal Counseling?

1. Couples who already have a child with some serious defect such as Down

syndrome, spina bifida, congenital heart disease, limb malformation, or

mental retardation

2. Couples with a family history of a genetic disease or mental retardation

3. Couples who are blood relatives (first or second cousins)

4. African Americans, Ashkenzzi Jews, Italians, Greeks, and other high-risk

ethnic groups

5. Women who have had a serious infection early in pregnancy (rubella or

toxoplasmosis) or who have been infected with HIV

6. Women who have taken potentially harmful medications early in

pregnancy or habitually use drugs or alcohol

7. Women who have had X rays taken early in pregnancy

8. Women who have experienced two or more of the following: stillbirth,

death of a newborn baby, miscarriage

9. Any woman thirty-five years or older

Source: Adapted from Fienbloom & Forman (1987) p. 129

The Concept of Range of Reaction for Intellectual PerformanceIn

tell

ectu

al P

erfo

rman

ce (

IQ)

High

Restricted Enriched

Average

Average

child A child B child C

Rea

ctio

n R

ange

Low

Type of Environment

KEY COMPARISONSTYPE OF STUDY OBJECTIVE

Same geneticrelatedness,differentenvironments

Twin

Adoption

Differencesin geneticrelatedness,same environment

Identical twinstogether

Identical twinsapart

Identical twinstogether

Fraternal twinstogether

Measuring the effects of Nature and Nurture: Twin and Adoption Studies

+0.10

+0.20

+0.30

+0.40

+0.50

+0.60

+0.70

+0.80

+0.90

+1.00

Cor

rela

tion

of IQ

sco

res

Identical twins reared together

Identical twins reared apart

Non-identical twins reared together

Siblings reared together

Siblings reared apart

Unrelated children reared together

Unrelated children reared apart

Correlations of IQ Scores

Ris

k

Prevalence ingeneral population

Fraternal twins

20

10

Major depression

Identical twins

Bipolar disorder

Prevalence ingeneral population

Fraternal twins

Identical twins

40

30

60

50

80

70

Blastocyst CleavageMorula Zygote

Fertilization

Ovulation

Maturefollicle

Implantationbeginning

Developingfollicles

Uterinewall

Ovary

Uterus

Cervix

Vagina

Fallopian tube

5 6

4

7

3 2 1

The Germinal Stage of Prenatal Development

Zygote Implantation of the Embryo

Fallopian tube

Ovary

Uterus

Cervix

Vagina

Embryo joinedto uterine wall

Ovary

Blastocyst

Fallopian tube

Conception

ImplantationFirstmissedperiod

Secondmissedperiod

OvumZygoteEmbryo

7 6 5 4 3 2 1 0

Weeks since fertilization

4 weeks 6 ½ weeks

7 weeks 9 weeks

15 weeks

Development During the Embryonic and Fetal Stages

Cell culture

Cells

Chromosome analysisBiochemical tests

Amniotic fluid

CentrifugeUterine wall

Placenta

Chorion

Amnioticfluid

Cell

Full termFetal period (in weeks)Embryonic period (in weeks)

3820 361612876543

Central nervous system

Heart

Period when majorabnormality occurs

Leg TeethArm

Eye

EyeHeart

Brain

Ear Palate Ear

External genitalia

Central nervous system

Heart

Arms

Eyes

Legs

Teeth

Palate

Period when minor defect orabnormality occurs

External genitalia

Ear

Occupation

Cleaning Personnel

Electronic Assemblers

Hair Dressers and Cosmetologists

Health Personnel

Painters

Photographic Processors

Plastic Workers

Printing Personnel

Textile and Garment Workers

Transportation Personnel

Soaps, detergents, solvents

Lead, tin, antimony, trichloroethylene, methyl chloride, resins

Hair-spray resins, aerosol propellants, solvents, dyes

Anesthetic gases, x-rays, laboratory chemicals

Lead, titanium, toluene

Caustics, bromides, iodides, silver nitrate

Formaldehyde, vinyl chloride

Ink mists, methanol, carbon tetrachloride, lead, solvents, trichloroethylene

Formadehyde, dyes, asbestos, solvents, flame retardants

Carbon monoxide, lead

Hazardous Substances

Nutrient

Folic acidVitamin DIronCalciumPhosphorusPyridoxineThiaminZincRiboflavinProteinIodineVitamin CEnergyMagnesiumNiacinVitamin B-12Vitamin A

180 mcg5 g15 mg800 mg1.6 mg1.1 mg12 mg1.3 mg50 g150 mcg60 mg2200 kcal280 mg15 mg2.0mcg800g

Pregnant

400 mcg10g30 mg1200 mg1200 mg2.2 mg1.5 mg15 mg1.6 mg60 g175 mcg70 mg2500 kcal320 mg17 mg2.2 mcg800 g

Percent Increase

+122+100+100

+50+50+38+36+25+23+20+17+17+14+14+13+10

0

Dietary Sources

Leafy vegetables, liverFortified dairy productsMeats, eggs, grainsDairy productsMeatsMeats, liver, enriched grainsEnriched grains, porkMeats, seafood, eggsMeats, liver, enriched grainsMeats, fish, poultry, dairyIodized salt, seafoodCitrus fruits, tomatoesProteins, fats, carbohydratesSeafood, legumes, grainsMeats, nuts, legumesAnimal proteinsDark green, yellow, or orange fruits and vegetables, liver

Nutritional Need Differences Between Nonpregnant and Pregnant Women (24 years old)

Nonpregnant

Source: Data from Reece et al., 1995.

Spine

BladderPubic boneCervixVagina

Coccyx Rectum

Potential width of birth canal

The baby in the uterus before labor Water about to break (The baby's head now rests inside the cervix)

Transition: The baby in the birth canal

The baby about to be born The head rotates sideways after it emerges The delivery of the placenta

STAGE 1

STAGE 2 STAGE 3

Prenatal Risk Factors

Genetic Abnormalities (Down Syndrome, PKU, Huntington’s

Disease, Sickle Cell, etc.)

Teratogen Exposure (alcohol, drugs, AIDS, DES, tobacco,

Thalidomide, etc.)

Maternal Age (Over 40 or under 18)

Maternal Malnutrition

Low SES

Lack of Prenatal Care

Genetic Abnormalities (Down Syndrome, PKU, Huntington’s

Disease, Sickle Cell, etc.)

Teratogen Exposure (alcohol, drugs, AIDS, DES, tobacco,

Thalidomide, etc.)

Maternal Age (Over 40 or under 18)

Maternal Malnutrition

Low SES

Lack of Prenatal Care