Chapter 2 - Ppt
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Transcript of Chapter 2 - Ppt
Biological Foundations: Heredity, Prenatal
Development, & BirthCh. 2
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
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
Mechanisms of Hereditycont’d
• Genes • Genotype • Phenotype
Alleles
• Characteristics determined by interaction of genes
• Each chromosome of pair contains one parent’s contribution
Allelescont’d
• Homozygous Alleles– Alleles are the same – Biochemical instructions on the allele
are followed
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
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)
Genetic Disorderscont’d
• Can be the result of extra, missing, or damaged chromosomes
• Example: Down’s Syndrome– Extra 21st chromosome
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
11
Klinefelter’s Syndrome
12
Turner Syndrome
Heredity, Environment, & Development
• Behavioral genetics – Focuses on the inheritance of
behavioral & psychological traits– Complex – not “either-or” but a range
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
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
What Twin Studies Can Teach Us
• Fraternal twins – no more genetic similarity than other
siblings
• Identical twins – genetically identical
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
From Conception to Birth
Prenatal Development
• Average of 38 weeks• Begins when sperm fertilizes egg• Encompasses the changes that
turn fertilized egg into a newborn human
Period of the Zygote
• Weeks 1-2• Fertilization begins this period• Period ends when zygote is
implanted in the wall of the uterus
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
Period of the Embryocont’d
• Amniotic sac fills with fluid• Umbilical cord connects embryo to
placenta• Principles of growth:
1. Cephalocaudal Principle2. Proximodistal Principle
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
Conception in the 21st Century
• In vitro fertilization• Inserting sperm directly into the
Fallopian tubes• Injecting sperm directly into the
egg
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
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
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
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
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
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
How Teratogens Influence Prenatal Development
• Each teratogen affects a specific aspect of prenatal development
• Damage from teratogens is not always evident at birth
Prenatal Diagnosis and Treatment
• Genetic Counseling• Helps to assess the chances of
inherited disorders
• Prenatal Diagnosis• Ultrasound
• Amniocentesis
• Chorionic Villus Sampling
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
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
Stages of Labor
• Stage 3 • lasts a few minutes • expelling of the placenta
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
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
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
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
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
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
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
Maternal Depression
• Infants & children of depressed mothers show cognitive & perceptual deficits
• Mothers who may be experiencing depression need to seek assistance