Chapter 2 - Ppt

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Biological Foundations: Heredity, Prenatal Development, & Birth Ch. 2

Transcript of Chapter 2 - Ppt

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Biological Foundations: Heredity, Prenatal

Development, & BirthCh. 2

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Mechanisms of Heredity

• Chromosomes – Thread like structures in the nucleus

that contain genetic material• 23 pairs of chromosomes– 22 pairs of autosomes– Sex chromosomes – XY = Boy– XX = Girl– Contain around 30,000 genes

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Mechanisms of Hereditycont’d

• Deoxyribonucleic acid (DNA) – Composed of 4 nucleotide bases that

are the biochemical basis of heredity• Nucleotide bases• Adenine• Thymine• Guanine• Cytosine

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Mechanisms of Hereditycont’d

• Genes • Genotype • Phenotype

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Alleles

• Characteristics determined by interaction of genes

• Each chromosome of pair contains one parent’s contribution

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Allelescont’d

• Homozygous Alleles– Alleles are the same – Biochemical instructions on the allele

are followed

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Allelescont’d

• Heterozygous Alleles– The parents have contributed different

versions of the trait– Instructions of the dominant allele are

followed– The recessive allele are ignored

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Genetic Disorders

• Can Result from inheriting harmful genes

• Genes usually carried by recessive alleles

• Examples:– Sickle – cell disease – Phenylketonuria (PKU)

• Huntington’s disease – (exception: caused by dominant allele on chromosome 4)

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Genetic Disorderscont’d

• Can be the result of extra, missing, or damaged chromosomes

• Example: Down’s Syndrome– Extra 21st chromosome

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Genetic Disorderscont’d

• Abnormal sex chromosomes• Common disorders

1. Klinefelter’s syndrome – XXY2. XYY complement – XYY3. Turner’s syndrome – X4. XXX syndrome – XXX

• No disorders consisting of just Y chromosome

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Klinefelter’s Syndrome

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Turner Syndrome

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Heredity, Environment, & Development

• Behavioral genetics – Focuses on the inheritance of

behavioral & psychological traits– Complex – not “either-or” but a range

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Polygenic Inheritance

• When many genes affect the phenotype of a trait

• Many psychological and behavioral characteristics

• impossible to trace to a single gene• Example : Extrovert/Introvert

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Twins

• Dizygotic (fraternal) twins – two different eggs fertilized by two

different sperm

• Monozygotic (identical) twins – the union of one egg and one sperm

that splits in two soon after conception

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What Twin Studies Can Teach Us

• Fraternal twins – no more genetic similarity than other

siblings

• Identical twins – genetically identical

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Paths From Genes to Behavior

• Genes’ impact on behavior depend on the environment– Reaction range

• Heredity and environment interact• Genes can influence the kind of

environment to which a person is exposed

• Environmental influences typically make children within a family different

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From Conception to Birth

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Prenatal Development

• Average of 38 weeks• Begins when sperm fertilizes egg• Encompasses the changes that

turn fertilized egg into a newborn human

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Period of the Zygote

• Weeks 1-2• Fertilization begins this period• Period ends when zygote is

implanted in the wall of the uterus

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Period of the Embryo

• Weeks 3-8• Body structures & internal organs

develop• 3 layers begin to form:

1. Ectoderm – outer layer2. Mesoderm – middle layer3. Endoderm – inner layer

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Period of the Embryocont’d

• Amniotic sac fills with fluid• Umbilical cord connects embryo to

placenta• Principles of growth:

1. Cephalocaudal Principle2. Proximodistal Principle

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Period of the Fetus

• Weeks 9-38–Week 9- Differentiation of the ovaries

and testes–Week 12- Circulatory system begins

to function–Week 16- Movement felt by mother–Week 32- Age of viability

• Fetus begins to behave• Senses work

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Conception in the 21st Century

• In vitro fertilization• Inserting sperm directly into the

Fallopian tubes• Injecting sperm directly into the

egg

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General Risk Factors

• Nutrition– Inadequate maternal nutrition may

result in premature birth and low birth weight

– Lack of folic acid may increase risk of spina bifida

• Stress– Studies show extreme maternal

stress is associated with low birth weight and premature births

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General Risk Factors(Cont)

• Mother’s Age– Older mothers are more likely to

have difficulty getting pregnant, miscarriages, and stillbirths

–Nearly 50% of pregnancies among women in their 40s and 50s result in miscarriage

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Teratogens: Drugs

• Known harmful agents include:– Alcohol, aspirin, caffeine, nicotine

• Fetal Alcohol Syndrome– Results from overuse of alcohol

during pregnancy– Children with FAS may have mental

retardation, facial deformities, and heart defects

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Teratogens: Diseases

• AIDS, Cytomegalovirus, Genital Herpes, Rubella (German Measles), Syphilis

• Effects include: – neurological disorders– deafness – blindness–mental disability – damage to bones, eyes, ears, or heart

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Teratogens: Environmental Hazards

• Lead, Mercury, PCBs, X-Rays• Effects may include: –mental disability– retarded growth– cerebral palsy– impaired memory and verbal skill– retarded growth– leukemia

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How Teratogens Influence Prenatal Development

• The effect – depends upon the genotype of the

organism

• The impact – changes over the course of prenatal

development– depends on the dosage

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How Teratogens Influence Prenatal Development

• Each teratogen affects a specific aspect of prenatal development

• Damage from teratogens is not always evident at birth

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Prenatal Diagnosis and Treatment

• Genetic Counseling• Helps to assess the chances of

inherited disorders

• Prenatal Diagnosis• Ultrasound

• Amniocentesis

• Chorionic Villus Sampling

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Prenatal Diagnosis and Treatment

(Cont)

• Fetal Medicine– Administering medicine to the fetus– Fetal surgery to correct spina bifida

and circulatory problems– Genetic engineering involves

replacing defective genes with synthetic normal genes

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Stages of Labor

• Stage 1 • lasts 12-24 hours (first birth) • includes contractions • enlargement of the cervix to

approximately 10 centimeters

• Stage 2 • actual birth of the baby • lasts about an hour

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Stages of Labor

• Stage 3 • lasts a few minutes • expelling of the placenta

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Approaches to Childbirth

• Childbirth Classes teach• What to expect (pregnancy/delivery)• techniques to manage the pain of

childbirth

• Studies show that mothers who attend childbirth classes typically use less medication

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Birthing Alternatives

• Home Births• Less Expensive• Parents have more control over the

conditions• Birth problems are no more common

at home than at the hospital when pregnancy has been problem-free

• Birthing Centers• More home-like than hospitals, but in

a clinic setting independent of hospitals

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Labor and Delivery: Birth Complications

• Hypoxia, or inadequate blood and oxygen to baby

• Complications may result in cesarean section (C-section)

• Births before the 36th week are called premature or preterm

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Labor and Delivery: Birth Complications

• < 5.5 pounds = low birth weight• < 3.3 pounds = very low birth weight• < 2.2 pounds = extremely low birth

weight

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Infant Mortality

• Infant Mortality is the number of infants out of 1,000 births that die before the age of 1 year

• U.S. mortality rate is just under 1%, or 7 of 1000

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Infant Mortality

• 15 industrialized nations have lower infant mortality than U.S

• Possible factors include • low birth weight resulting from a lack

of free or inexpensive prenatal care • fewer paid leave of absences for

pregnant women

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Maternal Depression

• “Baby blues” – – initial excitement turns to irritation,

resentment, & crying

• 10-20% of mothers experience post partum depression

• Can have negative effects on mother – child interactions

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Maternal Depression

• Infants & children of depressed mothers show cognitive & perceptual deficits

• Mothers who may be experiencing depression need to seek assistance