Biological And Environmental Foundation

BIOLOGICAL AND ENVIRONMENTAL FOUNDATIONS
I. GENETIC FOUNDATIONS
A. The foundations of development are heredity and environment. Heredity supplies our genotype (genetic makeup), while heredity and environment combine to form the phenotype (observable characteristics). B. The Genetic Code
1. Chromosomes store and transmit genetic information. Each cell in the human body contains 23 pairs of chromosomes.
2. DNA (deoxyribonucleic acid) molecules make up chromosomes.
3. A gene is a segment of a DNA molecule which contains instructions for making proteins.
4. Mitosis is the process of cell duplication in which each new cell receives an exact copy of the original chromosomes.
C. The Sex Cells
1. Sex cells, also known as gametes, are the sperm in males and the ova in females.
2. Meiosis is the process of cell division through which gametes are formed. It halves the number of chromosomes so each gamete contains 23.
3. In meiosis, the chromosomes pair up and exchange segments in a process called crossing over, so that genes from one are replaced by genes from another. Then chance determines which member of each pair will gather with others and end up in the same gamete.
4. Meiosis leads to variability among offspring. When sperm and ovum unite at conception, the resulting zygote has 46 chromosomes - 23 from each parent.
D. Boy or Girl?
1. The 22 pairs of matching chromosomes within a human cell are called the autosomes.
2. The twenty-third pair consists of sex chromosomes. Females have an XX pair of sex chromosomes; males have an XY pair.
3. The sex of the new organism is determined by whether an X-bearing or a Y-bearing sperm fertilizes the ovum.
E. Multiple Births
1. Fraternal, or dizygotic, twins result when two separate ova are fertilized by two separate sperm. 2. Identical, or monozygotic, twins result when a single zygote that has started to duplicate separates into two clusters of cells that develop into two individuals. Monozygotic twins have the same genetic makeup.
F. Patterns of Genetic Inheritance
1. Two forms of each gene occur at the same place on the autosomes, one inherited from the mother and one from the father. Each different form of the gene is called an allele.
2. If the genes from both parents are alike, the child is homozygous and will display the inherited trait. If they are different, then

the child is heterozygous, and relationships between alleles determine the trait that will appear. 3. Dominant-recessive inheritance is a pattern where, in a heterozygous situation, only one gene's influence is exhibited
a. The gene that is dominant is expressed; the gene that is recessive is not expressed.
b. An individual who is heterozygous is a carrier who can pass a recessive gene to his or her children.
c. Modifier genes often act on alleles, slightly altering their effects.
d. PKU is one of the most frequently occurring recessive disorders.
e. Dominant genes rarely transmit serious diseases from one generation to the next, since the individual usually does not live long enough to pass the gene to the next generation. An exception is
Huntington disease.
4. Codominance is a pattern of inheritance in which both alleles influence the person's characteristics. a. The sickle cell trait is a heterozygous condition present in many black Africans.
b. Sickle cell anemia occurs in full form when a child inherits two recessive alleles.
5. X-linked inheritance occurs when a recessive allele is carried on the X chromosome.
Males are more likely to be affected, since the Y chromosome is not as long as the X and may not have a corresponding dominant gene to override the recessive gene.
a. Red-green color blindness is one example of an X-linked recessive trait.
b. Hemophilia, a disorder in which the blood fails to clot normally, is also an X-linked disease. 6. In a pattern of inheritance known as genetic imprinting, some genes are chemically marked (or imprinted) in such a way that one pair member (which can come from either the mother or the father) is activated regardless of its makeup.
a. Imprinting is involved in several childhood cancers and in Praeder-Willi syndrome, which is characterized by mental retardation and obesity.
b. Genetic imprinting can also operate on the sex chromosomes, producing fragile X syndrome. 7. Harmful genes are created when a mutation, a sudden and permanent change in a DNA segment, takes place, either by chance or as a result of hazardous substances in the environment.
8. Complex traits follow polygenic inheritance, in which many genes are involved in determining the characteristic.
G. Chromosomal Abnormalities
1. Most chromosomal defects occur during the process of meiosis. Because these abnormalities involve more DNA than single-gene disorders, they often produce disorders with many mental and physical symptoms. 2. Down Syndrome
a. This disorder results when the twenty-first pair of chromosomes fail to separate during meiosis.

b. The individual inherits three chromosomes rather than the normal two and this disorder is sometimes called trisomy 21.
c. Symptoms include distinct physical features, mental retardation, speech problems, and slow motor development. d. The risk of Down syndrome increases dramatically with maternal age.
3. Abnormalities of the Sex Chromosomes
a. Sex chromosome disorders usually result in fewer problems than defects of the autosomes and are often not recognized until adolescence.
b. A variety of myths about individuals with sex chromosome disorders exist. For example, it is often erroneously believed that males with XYY syndrome are more aggressive and antisocial than XY males. c. Research indicates that adding to or subtracting from the usual number of X chromosomes results in particular intellectual deficits.
II. REPRODUCTIVE CHOICES
A. Due to advances in genetic counseling and prenatal diagnosis, people can make informed decisions regarding conceiving, carrying a pregnancy to term, or adopting a child.
B. Genetic counseling allows a couple to assess the likelihood of giving birth to a baby with a hereditary disorder.
C. Prenatal Diagnosis and Fetal Medicine
1. Prenatal diagnostic methods permit detection of problems before birth by utilizing certain medical procedures such as amniocentesis, chorionic virus sampling, ultrasound, and maternal blood analysis.
2. Improvements in prenatal diagnosis have led to advances in fetal medicine; some problems can be treated before birth.
Nevertheless, these practices remain controversial.
3. The goal of today's genetic engineers is to map chromosomes and to correct hereditary defects with genetic repair or replacement. D. The Alternative of Adoption
1. Because the availability of healthy babies has declined, more people are adopting from foreign countries or taking children who are older or who have developmental problems.
2. Although it is not high, the risk of initial adoption failure is greatest for handicapped and older children.
3. Adopted children and adolescents have more emotional and learning problems than occur in the general child population.
4. Most adopted children have happy childhoods and grow up to be well-adjusted adults.
III. ENVIRONMENTAL CONTEXTS FOR DEVELOPMENT

A. The child's environment consists of many influences that combine to affect the course of development. These factors include family, friends, school, experiences, and society in general.
B. The Family
1. Family members can influence one another directly and indirectly. In indirect influences, a third party can support or undermine other family relationships.
2. The family is a dynamic, ever-changing system that can be modified by important life events. The developmental status of each family member and the historical time period also contribute to a dynamic family system.
3. Despite the family's flexible and changing nature, parental responsiveness and reasonable demands for mature behavior are crucial features of effective parenting.
C. Socioeconomic Status and Family Functioning
1. Socioeconomic status (SES) is an index of a family's or individual's social position and economic well-being. It combines years of education, prestige and skill of one's job, and income.
2. SES differences in values and behaviors are apparent in child-rearing practices. These differences may be attributed both to varying life conditions and to differing educational levels.
3. Lower-SES parents value external characteristics (e.g. obedience and neatness) and are more restrictive in interactions with their children.
4. Higher-SES parents value psychological traits (e.g. happiness and curiosity) and more often engage in verbal interaction with their children.
5. SES is positively correlated with cognitive and language development and academic success. D. The Impact of Poverty (pp. 77-78)
1. Those most affected by poverty are parents under 25 with young children, elderly people who live alone, ethnic minorities and single mothers with preschool children.
2. Poverty is more widespread among children than any other age group. joblessness, a high divorce rate, a high rate of adolescent childbearing, and inadequate government funding contribute to the high rate of poverty for children.
3. The constant stress of poverty weakens the family system.
a. Parents experience many daily hassles and crises, which reduce their ability to effectively deal with the children. b. Poor housing and dangerous neighborhoods increase the stress levels of impoverished families. c. Homeless children suffer from developmental delays, emotional stress, health problems, school absenteeism, and poor academic performance.

E. Beyond the Family: Neighborhoods, Schools, Towns, and Cities (pp. 78-80)
1. Child abuse and neglect are greatest where residents describe the community as a socially isolated place to live. Family stress and child adjustment problems are reduced when family ties to the community are strong.
2. Neighborhoods
a. Children are better adjusted socially and emotionally when their neighborhood experiences are more varied.
b. Neighborhood resources have a greater impact on young people growing up in economically disadvantaged than well-to-do neighborhoods.
c. In low-income areas, social ties that link families to one another and to other institutions are weak or absent.
Consequently, informal social controls over young people weaken, giving rise to antisocial activities.
3. Schools
a. School is a formal institution designed to transmit knowledge and skills that children need to become productive members of society.
b. Schools differ in the quality of their physical environments, educational philosophies, and social life.
c. Regular contact between families and teachers supports children's development, consistent with the mesosystem in ecological systems theory.
4. Towns and Cities
a. Small towns have fewer cultural experiences available than cities. However, small towns offer greater community involvement and safer environments for children.
b. Community life is especially undermined in high-rise urban housing projects.
F. The Cultural Context
1. Cultural Values and Practices
a. Cultures shape family interaction, school experiences, and community settings beyond the home.
b. Independence, self-reliance, and the privacy of family life are central values among
American middle-class families. c. In large industrialized countries such as the United States, subcultures exist in which groups of people share beliefs and customs different from the larger culture.
d. Some cultural traditions promote extended family households, in which a parent and child live with one or more adult relatives.
e. In collectivist societies, people define themselves as part of a group and stress group over individual goals.
f. In individualistic societies, people think of themselves as separate entities and are largely concerned with their

own goals. The United States is more individualistic than most other industrialized nations. 2. Public Policies and Child Development
a. Public policies are laws and government programs that attempt to improve conditions for children and families by responding to current social problems.
b. For a variety of reasons, the United States lags behind other Western nations in developing policies that benefit children and families. These reasons include the values of self-reliance and privacy and the cost of social programs. 3. Contemporary Progress in Meeting Children's Needs
a. Public policy fostering children's development is justified on the grounds that they have basic rights as human beings and are the future adult members of our society.
b. Many government-sponsored child and family programs are crisis oriented, and funding for these efforts has been inconsistent. However, new policy initiatives are underway to improve the status of American children.
c. The National Association for the Education of Young Children (NAEYC) has taken a strong leadership role in establishing accreditation systems for preschool and day care centers.
d. The Children's Defense Fund is an influential interest group whose focus is the wellbeing of children.
IV. UNDERSTANDING THE RELATIONSHIP BETWEEN HEREDITY AND
EVIRONMENT
A. The Question, "How Much?"
1. Heritability
a. Heritability estimates measure the extent to which individual differences in complex traits (e.g., intelligence and personality) are due to genetic factors.
b. Heritability estimates are obtained from kinship studies, which compare characteristics of family members.
c. The most common kinship studies compare identical and fraternal twins.
d. Kinship studies of intelligence have provided controversial findings.
2. Concordance
a. The concordance rate refers to the percentage of instances in which both twins show a trait when it is present in one pair member. For a trait to be attributed solely to heredity, the rate for identical twins would have to be 100 percent. b. Concordance and adoption research suggests a strong genetic component underlying schizophrenia and depression, although the environment is also involved.
3. Limitations of Heritability and Concordance

a. Concerns about the accuracy and usefulness of heritability estimates and concordance rates have been expressed. b. They can overestimate the impact of heredity while underestimating the importance of environment.
c. It is difficult to generalize the twin pair study results to the general population.
d. Although they provide useful information, they do not address the process of development. Results can be misapplied. B. The Question, "How?"
1. Some believe that heredity and environment are intricately entwined and cannot be divided into separate influences.
2. Reaction Range
a. A range of reaction is a person's unique, genetically determined response to a range of environmental conditions. This accounts for how children respond in different ways to the same environment. b. Unique blends of heredity and environment lead to both similarities and differences in behavior. 3. Canalization
a. Canalization is the tendency of heredity to restrict development to one or a few potential outcomes. Highly canalized traits require extreme environmental conditions to deter their genetically set outcomes. b. We now know that environments can also limit development.
4. Genetic-Environmental Correlation
a. The concept of genetic-environmental correlation states that our genes influence the environments to which we are exposed.
b. Passive and Evocative Correlation
1) In a passive correlation, a child has no control over the environment available to him or her.
Parents create an environment compatible with their own heredity.
2) In an evocative correlation, a child behaves in ways consistent with his or her own heredity.
The responses evoked from others will, in turn, strengthen the child's original response. c. Active Correlation
1) An active correlation is more common at older ages. As children extend their experiences beyond the immediate family, they choose environments that complement their genetic tendencies.
2) This tendency to actively choose environments that complement our heredity is called niche-picking.
3) With age, genetic factors may become more important in determining the environments we experience and choose for ourselves.