THE START OF LIFE: PRENATAL DEVELOPMENT

THE START OF LIFE: PRENATAL DEVELOPMENT
Chapter 2 THE START OF LIFE: PRENATAL DEVELOPMENT Copyright © 2011 Pearson Education, Inc. All rights reserved.

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 the 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 DEFINE: GAMETES-male and female reproductive cells

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 At the moment of conception, humans receive about 25,000 genes, contained on 46 chromosomes in 23 pairs. Define: GENES: basic unit of genetic information DNA (deoxyribonucleic acid molecule) CHROMOSOMES 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 Define: MOMOGYGOTIC: genetically identical DIZYGOTIC: two separate ova

Establishing the Sex of the Child
When an ovum and sperm meet at the moment of fertilization, the ovum is certain to provide an X chromosome, while the sperm will provide either an X or a Y chromosome. If the sperm contributes its X chromosome, the child will have an XX pairing on the twenty-third chromosome and will be a girl. If the sperm contributes a Y chromosome, the result will be an XY pairing—a boy. Does this mean that girls are more likely to be conceived than boys? Copyright © 2011 Pearson Education, Inc. All rights reserved.

Mixing and Matching of Genes
Basics of genetics Dominant traits Recessive traits Polygenic traits Define: DOMINANT TRAITS: expressed RECESSIVE: not expressed (displaced)

Just the right type Genotype Homozygous Heterozygous Phenotype Define:
GENOTYPE: underlying combination of genetic material present PHENOTYPE: observable trait HOMOZYGOUS: allele contains similar genes from each parent HETEROZYGOUS: allele contains different forms of genes from parents

Genetic Information Transmission
PKU, a disease that causes brain damage and mental retardation, is produced by a single pair of genes inherited from one's mother and father. If neither parent carries a gene for the disease (a), a child cannot develop PKU. Even if one parent carries the recessive gene, but the other doesn’t (b), the child cannot inherit the disease. However, if both parents carry the recessive gene (c), there is a 1 in 4 chance that the child will have PKU. Ask: What is PKU? Define: POLYGENETIC INHERITANCE: combination of multiple gene pairs responsible for production of a particular trait X-LINKED GENES: recessive genes located on X chromosomes

Cracking the Genetic Code
The Human Genome National Human Genome Research Institute

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 Disease Klinefelter's Syndrome Define: Down Syndrome: extra chromosome on 21st pair; 1 in 500/higher in older mothers Fragile X Syndrome: Fragile X syndrome is the most common form of inherited mental retardation in males and a significant cause in females. The inheritance is different from common dominant or recessive inheritance patterns. A fragile area on the X chromosome (called FMR1) has repeats in the genetic code. The more repeats, the more likely there is to be a problem. Boys and girls can both be affected, but because boys have only one X chromosome, a single fragile X is likely to affect them more severely. Sickle-cell Anemia: Sickle cell anemia is an inherited disease in which the red blood cells, normally disc-shaped, become crescent shaped. As a result, they function abnormally and cause small blood clots. These clots give rise to recurrent painful episodes called "sickle cell pain crises." Sickle cell anemia is inherited as an autosomal recessive trait , which means it occurs in someone who has inherited hemoglobin S from both parents. Sickle cell disease is much more common in certain ethnic groups, affecting approximately one out of every 500 African Americans. Tay-Sachs Disease: Tay-Sachs disease is a familial disorder (it affects more than 1 member of a family) that results in early death. It is found predominantly in Ashkenazi Jewish families. An enzyme deficiency that interferes with metabolism of crucial nerve tissue chemicals. Tay-Sachs disease is inherited as a recessive gene, and 1 in 25 members of the Ashkenazi Jewish population carries the gene. Klinefelter's Syndrome: Klinefelter syndrome is a chromosome disorder in males. People with this condition are born with at least one extra X chromosome. Klinefelter syndrome is one of the most common chromosomal abnormalities. About one in every 500 to 800 males is born with this disorder. Approximately 3% of the infertile male population have Klinefelter syndrome.

Behavioral Genetics Inhaled Air and Genetic Mutations
Inhalation of unhealthy, polluted air may lead to mutations in genetic material in sperm. These mutations may be passed on, damaging the fetus and affecting future generations.

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

These are susceptibility tests that provide only an estimated risk for developing the disorder.
(Source: Human Genome Project, 2010,

Are “Designer Babies” in Our Future?
Should pre-implantation genetic diagnosis (PGD) be available to all families? For selecting gender of child? For PGD? For couples with a high risk of transmitting an inherited condition to help couples identify embryos carrying a genetic disease or a chromosome abnormality, thus avoiding the difficult choice of abortion. In addition, there are infertile couples who carry an inherited condition and who opt for PGD as it can be easily combined with their IVF treatment.

REVIEW Review and Apply
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. male; female; 23 genotype; phenotype Behavioral genetics

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. inherited; genetic genetic counselors

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. Ask students: Yes or no? See example using temperament. MULTIFACTORIAL TRANSMISSION: many traits determined by combination of both genetic and environmental factors; genotype provides particular range within which a phenotype may achieve expression; in many cases the environment determines the way in which a particular genotype will be expressed as a phenotype

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 It is the unique interaction of inherited and environmental factors that determines people's patterns of development. Copyright © 2011 Pearson Education, Inc. All rights reserved.

Range of Possibilities: Determinants of Intelligence
Ask: What becomes the most appropriate question? How much of the behavior is caused by genetic factors and how much by environmental factors?

Studying Development How Much Is Development? How Much Is Nature?
Nonhuman animal studies Controlling genetics and environment Human studies Adoption Twin studies Family studies Ask: Which approach best addresses the nature/nurture best? General conclusion: virtually all traits, characteristics, and behaviors are joint result of the combination and interaction of nature and nurture. Genetic and environmental factors work in tandem, affecting and being affected by the other, creating the unique individual that each of us is and will become

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 Define: Monozygotic twins: best example of relationship between genetic similarity and shared physical characteristics

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 What motivates this research? Intelligence (as measured) by IQ score) is central human characteristic that differentiates humans from other species IQ scores of identical twins become increasingly similar over time This does not discount importance of environmental influence on intelligence

Genetics and I.Q. The closer the genetic link between two individuals, the greater the correspondence between their IQ scores. Why do you think there is a sex difference in the fraternal twins’ figures? Might there be other sex differences in other sets of twins or siblings, not shown on this chart?

Do we inherit our personality?
Research evidence indicates some of most basic personality traits have genetic roots

Two* of “Big Five” personality traits linked to genetic factors:
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?
These traits are among the personality factors that are related most closely to genetic factors. The higher the percentage, the greater the degree to which the trait reflects the influence of heredity. Do these figures mean that “leaders are born, not made”? Why or why not? Examination reveals specific gene very influential in determining risk-taking (novelty-seeking gene affects production of dopamine) Twins reared apart studies: certain traits reflected contribution of genetics considerably more than others Some less basic personality trait links: political attitudes, religious interests and values, attitudes toward human sexuality

Psychological Disorders: The Role of Genetics and the Environment
Culture Parental encouragement Can you think of any others? Ask: What kinds of environmental influence is seen today to affect personality development? Media World events?

Developmental Diversity
Can a culture's philosophical outlook be determined by genetics? Are there “good” and “bad” cultures? This question addresses the notion that the very basis of cultures-its philosophical traditions-may be affected by genetic factors

Mean Behavioral Scores for Caucasian American, Irish, and Chinese 4-Month-Old Infants
Shows clears differences in temperament between Caucasian and Asian children Does NOT mean one philosophical approach is necessarily better than the other Individual differences occur within every culture Interplay between genetics and culture influence temperament These data also illustrate that genetics alone does not influence the development of the disorder. If genetics were the sole cause, the risk for an identical twin would be 100 percent. Consequently, other factors account for the disorder, ranging from structural abnormalities in the brain to a biochemical imbalance (e.g., Lyons, Bar, & Kremen 2002; Hietala, Cannon, & van Erp 2003; Howes & Kapur 2009; Wada et al. 2012).

The Genetics of Schizophrenia
The psychological disorder of schizophrenia has clear genetic components. The closer the genetic links between someone with schizophrenia and another family member, the more likely it is that the other person will also develop schizophrenia. (Source: Based on Gottesman, 1991.) Copyright © 2011 Pearson Education, Inc. All rights reserved.

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 Use schizophrenia information to elaborate on this See Figure 2.11

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

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. genetic; environmental physical; intelligence; personality; psychological predisposed genetically

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
Define: Sperm: shorter life span; 100 million produced daily; 300 million typically ejaculated; only small fraction reach ovum Ovum: 400,000 at birth (in ovaries); do not mature until puberty; ovulate every 28 days Zygote

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 Define: Placenta Umbilical cord

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 Define: Ectoderm: form skin, hair, teeth, sense organs, brain, spinal cord Endoderm: inner layer forms digestive system, liver, pancreas, respiratory system Mesoderm: sandwiched between other two and forms muscles, bones, blood, circulatory system At end of embryonic stage: 1 inch long, gills and tail-like structure; rudimentary eyes, lips, teeth, stubby bulges that become arms and legs; head grows rapidly and begins to represent significant portion of body (50% of total length); rapid growth of nerve cells (100,000 neurons produced EVERY MINUTE); nervous system begins to function at 3 weeks and at 5 weeks weak brain waves detected

Body Proportions During the fetal stage, the proportions of the body change dramatically. At two months, the head represents about half the fetus, but by the time of birth, it is one-quarter of its total size. 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 Rapid development Increases in length 20 times and proportions change dramatically See Figure 2.13 At 4 months = 4 ounces; at 7 months = 3 pounds; at birth = 7 pounds Brain waves indicate several different stages of sleep and wakefulness; hear and feel vibrations Hormones released between 8 and 24 weeks that lead to gender differentiation No two fetuses are alike; broad similarities in sequence of development Differences due to genetics and the environment of womb

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 Infertility: 15% of couples; inability to conceive after 12 to 18 months Maternal infertility influenced by age; hormone imbalance, damaged fallopian tubes or uterus, stress, abuse of alcohol or drugs Paternal infertility influenced by illicit drugs, tobacco, STDs Artificial insemination; IVF; GIFT; ZIFT; ethical issues Miscarriage: spontaneous abortion; 15-20% pregnancies ends in miscarriages; many times genetic abnormality Abortion: voluntary termination pregnancy; aftereffects; may contribute to increase in future pregnancies

Older Women and Risks of Pregnancy
Not only does the rate of infertility increase as women get older, but the risk of chromosomal abnormality increases as well. (Source: Reproductive Medicine Associates of New Jersey, 2002.) Copyright © 2011 Pearson Education, Inc. All rights reserved.

Threats to Development
Prenatal environment: Enter at your own risk! Teratogen (See Figure for a teratogen sensitivity timeline) Teratogen: environmental agent or other factor that produces a birth defect Timing and quantity of exposure crucial; sensitivity to specific teratogen related to racial and cultural background; different organ systems vulnerable at different times during development (e.g., brain development)

Teratogen Sensitivity Timeline
Depending on their state of development, some parts of the body vary in their sensitivity teratogens. (Source: Moore, 1974.)

Mother's Prenatal Influence
Diet Age Prenatal support Health Drug use Alcohol use Fetal alcohol syndrome (FAS) Fetal alcohol effects (FAE) Tobacco use Diet: mother's diet supports development of fetus; global concern; postnatal enrichment of prenatal undernourishment can sometimes overcome some of effects Age: More older women giving birth due to societal transformations; mothers over 30 at greater risk for variety pregnancy and birth complications; condition of ovum; Down syndrome; adolescent mothers more likely to deliver premature babies Prenatal support: Young mothers often face adverse social and economic factors which can affect infant health; social support and poverty contribute to lack of resources for prenatal support Mother's health: Rubella prior to 11th week of pregnancy; mumps increase miscarriage risk; syphilis directly transmitted to fetus; STD (gonorrhea) transmitted; AIDS (AZT during pregnancy reduces transmission to around 5%) Mother's drug use: poses serious risk to unborn child (legal, illegal, OTC drugs) Thalidomide DES: diethylstilbestrol to prevent miscarriage later raised daughter risk of vaginal/cervical cancer Birth control: fetal damage Illicit drugs: marijuana, cocaine (crack babies) Mother's alcohol use: even small amounts can disrupt development of fetus; FAS; FAE Mother's smoking: reduces oxygen content and increases carbon monoxide in mother's blood fetus respiration slows and heart beat increases and increases miscarriage risk (100,000 miscarriages caused by smoking); low birth weight; shorter; 50% more likely to have mentally retarded or disruptive child

Father's Prenatal Influence
Relatively little research Tobacco use Drug use Alcohol use Treatment of mother Father's influence: little research; secondhand smoke may influence mother's health; alcohol and drug use may impair sperm leading to chromosomal damage; may create stress; physical and emotional abuse can cause maternal stress

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

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 ____. conceive artificial insemination; in vitro fertilization germinal; embryonic; fetal

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. prenatal health; growth drugs; alcohol; tobacco; caffeine health

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?

THE START OF LIFE: PRENATAL DEVELOPMENT

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THE START OF LIFE: PRENATAL DEVELOPMENT

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