CHAPTER 2 THE START OF LIFE PRENATAL DEVELOPMENT

CHAPTER 2 THE START OF LIFE: PRENATAL DEVELOPMENT

Learning Objectives LO 2 -1 What is our basic genetic endowment and how can human development go off track? LO 2 -2 How do the environment and genetics work together to determine human characteristics? LO 2 -3 Which human characteristics are significantly influenced by heredity? LO 2 -4 How are human characteristics affected by the environment? LO 2 -5 What stages comprise prenatal development LO 2 -6 What are threats to the fetal environment what can be done about them?

EARLIEST DEVELOPMENT

Beginning of Life Humans begin life simply • Gametes from male and female join – ovum and sperm • Fused gametes create zygote • Resulting combination of their genetic instructions—over 2 billion chemically coded messages—is sufficient to begin creation of human

Contents of a Single Human Cell • Genes – Specific DNA sequences • Chromosomes – Rod-shaped DNA portions in 23 pairs – Contain genetic blueprint for individuals – Replicate through mitosis

Multiple Births: Two-or More-for the Genetic Price of One Are there different kinds of multiple births? • Monozygotic • Dizygotic • Trizygotic What causes multiple births? • Fertility drugs • Racial, ethnic, and national differences

Rising Multiples

Establishing the Sex of the Child

Mixing and Matching of Genes Basics of genetics • Dominant traits • Recessive traits • Polygenic traits

Just the right type Genotype • Homozygous • Heterozygous Phenotype

Genetic Information Transmission

Cracking the Genetic Code • The Human Genome • National Human Genome Research Institute • http: //www. genome. gov/

In what ways can information from the Human Genome Project affect your life?

Current Understanding of the Genetic Basis of Selected Disorders and Traits

When Development Deviates from the Norm Causes Genetics Spontaneous mutation Environmental insult

When Development Deviates Consequences Down Syndrome Fragile X Syndrome Sickle-cell Anemia Tay-Sachs Klinefelter's Disease Syndrome

Behavioral Genetics

Genetic Counseling: Predicting the Future from the Genes of the Present • Can you name three diseases for which DNA-based genetic tests are available? • (Hint: see Table 2 -3)

Fetal Development Monitoring Techniques

Are “Designer Babies” in Our Future? Should pre-implantation genetic diagnosis (PGD) be available to all families?

Review and Apply REVIEW • In humans, the ____ sex cell (sperm) and the ____ sex cell (ova) provide the developing baby with ____ chromosomes each. • A ____ is the underlying combination of genetic materials present in an organism, but invisible; a ____ is the visible trait, the expression of the genotype. • The field of ____, a combination of psychology and genetics, studies the effects of genetics on behavior.

Review and Apply REVIEW • Several ____ and ____ disorders are due to damaged or mutated genes. • ____ use a variety of data and techniques to advise future parents of possible genetic risks to their unborn children.

Review and Apply APPLY • How can the study of identical twins who were separated at birth help researchers determine the effects of genetic and environmental factors on human development?

THE INTERACTION OF HEREDITY AND ENVIRONMENT

What do you think? A given behavior is not caused just by genetic factors, nor is it caused solely by environmental factors.

Role of the Environment in Determining the Expression of Genes: From Genotypes to Phenotypes Given behavior is not caused just by genetic factors; nor is it caused solely by environmental forces • Multifactorial transmission

Range of Possibilities: Determinants of Intelligence

Studying Development How Much Is Development? How Much Is Nature? Nonhuman animal studies • Controlling genetics and environment Human studies • Adoption • Twin studies • Family studies

Do you have your mother's eyes? Family resemblances • More genetically similarity more likely to share physical characteristics • Obesity, blood pressure, respiration rates, age at death

Nature, Nurture, and Intelligence What motivates this research? • Relative contributions of nature and nurture highly researched • Closer genetic link = greater correspondence of overall IQ scores

Genetics and I. Q.

Do we inherit our personality?

Genetic and Environmental Influence on Personality: Born to Be Outgoing? Two* of “Big Five” personality traits linked to genetic factors: Neuroticism* Extroversion* Contentiousness Openness Agreeableness

What evidence supports this claim?

Psychological Disorders: The Role of Genetics and the Environment • Culture • Parental encouragement Can you think of any others?

Developmental Diversity Can a culture's philosophical outlook be determined by genetics? Are there “good” and “bad” cultures?

Mean Behavioral Scores for Caucasian American, Irish, and Chinese 4 -Month-Old Infants

The Genetics of Schizophrenia

Fundamental Principle Within debate about relative influence of nature and nurture • Role of genetics is often to produce tendency toward future course of development • Role of environment affects when and whether a certain behavioral characteristic will actually be displayed

Can Genes Influence the Environment? Sandra Scarr suggests three ways child's genetic predisposition may influence his or her environment: • Active • Passive • Evocative

Review and Apply REVIEW • Human characteristics and behavior are a joint outcome of ____ and ____ factors. • Genetic influences have been identified in ____ characteristics, ____ traits and behaviors, and ____ disorders. • There is some speculation that entire cultures may be ____ toward certain types of philosophical viewpoints and attitudes.

Review and Apply APPLY • How might an environment different from the one you have experienced have affected the development of personality characteristics that you believe you inherited from one or both of your parents?

PRENATAL GROWTH AND CHANGE

Fertilization: The Moment of Conception

Stages of Prenatal Development • Germinal • Embryonic • Fetal • (See Table 2 -5 for a concise review)

Stages of the Prenatal Period

Germinal Stage Fertilization two weeks • Shortest stage • Fertilized egg now called blastocyst • Travels to and implants in uterus • Characterized by methodical cell division • With division comes cell specialization

Embryonic Stage 2 weeks 8 weeks • Organism firmly secures to uterus and called an embryo • Development of major organs and basic anatomy Three distinct layers that ultimately form different set of structures • Ectoderm • Endoderm • Mesoderm

Body Proportions Why might this make infants especially susceptible to “Shaken Baby Syndrome? ”

Fetal Stage 8 weeks Birth • Formally starts when differentiation of major organs has occurred • Organism now called fetus • Characterized by rapid development – Organs become more differentiated and begin working – Interconnections between body parents become more complex and integrated – Brain becomes more sophisticated

Pregnancy Problems Infertility • IVF, GIFT, ZIFT Miscarriage • Risk for anxiety, depression, grief Abortion • Mixed findings related to after-effects • Generally short-term regret and guilt; increased risk of future psychological problems for some

Older Women and Risks of Pregnancy

Threats to Development Prenatal environment: Enter at your own risk! • Teratogen • (See Figure 2 -15 for a teratogen sensitivity timeline)

Teratogen Sensitivity Timeline

Mother's Prenatal Influence • • • Diet Age Prenatal support Health Drug use Alcohol use – Fetal alcohol syndrome (FAS) – Fetal alcohol effects (FAE) • Tobacco use

Father's Prenatal Influence • • • Relatively little research Tobacco use Drug use Alcohol use Treatment of mother

Becoming an Informed Consumer Optimizing the Prenatal Environment • Avoid X-rays and birth control pills; get rubella vaccination • Eat well and take prenatal vitamins • Avoid alcohol and other drugs • Monitor caffeine intake • Avoid smoking and exposure to secondhand smoke • Exercise regularly

Review and Apply REVIEW • Fertilization joins the sperm and ovum to start the journey of prenatal development. Some couples, however, need medical help to ____. • Among the alternative routes to conception are ____ and ____(IVF). • The prenatal period consists of three stages: ____, and ____.

Review and Apply REVIEW • The ____ environment significantly influences the development of the baby. • The diet, age, prenatal support, and illnesses of mothers can affect their babies’ ____ and ____. • Mothers’ use of ____, and ____ can adversely affect the health and development of the unborn child. • Fathers’ and others’ behaviors (e. g. , smoking) can also affect the ____ of the unborn child.

Review and Apply APPLY • Studies show that “crack babies” who are now entering school have a significant difficulty dealing with multiple stimuli and forming close attachments. How might both genetic and environmental influences combined to produce these results?

EPILOGUE Before moving on, return to the prologue of this chapter and the case of the Leyna Gonzalez, who was treated for a rare tumor before she even was born. Answer the following questions based on your understanding of genetics and prenatal development. • Do you believe that Leyna's parents made the correct decision in permitting the risky operation for their daughter? Why? • What would you speculate were the most likely reasons that Leyna developed the very rare tumor?

EPILOGUE • What kind of evidence would suggest that the tumor could be brought about by a combination of both genetic and environmental factors? • If there had been no treatment possible for Leyna's tumor, what do you think the best course of action would have been for her parents?