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Chapter Two Biological and Environmental Foundations Genetic Foundations: 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). Each of us is made up of trillions of cells. Chromosomes in the nucleus of the cell store and transmit genetic information. The Genetic Code: DNA (deoxyribonucleic acid) molecules make up e chromosomes. A gene is a segment of a DNA molecule which contains instructions for making proteins and ultimately making humans. What is Mitosis? Mitosis is the process of cell duplication in which each new cell receives an exact copy of the original chromosomes or how regular cells in our body reproduce. What are Sex Cells? Sex cells, also known as gametes, are the sperm in males and the ova in females. What is Meiosis? Meiosis is the process of cell division through which gametes are formed. It halves the number of chromosomes so each gamete contains 23. 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. Meiosis leads to variability among offspring. When sperm and ovum unite at conception, the resulting zygote has 46 chromosomes; 23 from each parent. A Boy or Girl? The 22 pairs of matching chromosomes within a human cell are called the autosomes. The twenty-third pair consists of sex chromosomes. Females have an XX pair of sex chromosomes; males have an XY pair. The sex of the new organism is determined by whether an X-bearing or a Y-bearing sperm fertilizes the ovum. Who determines the sex of the child?

Multiple Births: Fraternal, or dizygotic, twins result when two separate ova are fertilized by two separate sperm. 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. During their early years, children of single births are often healthier and develop more rapidly than do twins. Patterns of Genetic Inheritance: 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. 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. Dominant–recessive inheritance is a pattern where, in a heterozygous situation, only one gene’s influence is exhibited. The gene that is dominant is expressed; the gene that is recessive is not expressed. An individual who is heterozygous is a carrier who can pass a recessive gene to his or her children. What is PKU (Phenylkentonuria)? PKU is a recessive genetic disorder. It involves the inability to metabolize the amino acid phenylalanine, contained in many proteins, and causes severe central nervous system damage in the first year of life. A diet low in phenylalanine = normal mental development. Even small amounts of phenylalanine interfere with brain functioning –less cognitive and motor development appears in childhood into adulthood. 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. What is Huntington Disease? Huntington Disease is a dominant genetic disorder of the cenetral nervious system. The central nervous system degeneration which leads to muscular coordination difficulties, mental deterioration, and personality changes. Symptoms of Huntington’s Disease usually do not appear until age 35 or

later. By this age there is a high likelihood that the individual has had children and perhaps passed the dominant gene to his or her children. A codominant pattern is a pattern of inheritance in which both genes or alleles influence the person’s characteristics. The sickle cell traitis a heterozygous condition present in many black Africans, Latin, Arabs, India, Italians as Caucasians. Sickle cell anemia occurs in full form when a child inherits two recessive genes or alleles. What is sickle cell anemia? Sickle Cell Anemia is the abnormal sickling of red blood cells causes oxygen deprivation, pain, swelling and tissue damage. Anemia and susceptibility to infection, especial pneumonia. Abnormalities of the Sex Chromosomes: Sex chromosome disorders usually result in fewer problems than defects of the autosomes and are often not recognized until adolescence. 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. Researchers were trying to link aggressive behavior to chromosomal abnormalities. Research indicates that adding to or subtracting from the usual number of X chromosomes results in specific types of intellectual deficits. What is Down Syndrome? Down syndrome results when the twenty-first pair of chromosomes fail to separate during meiosis. The individual inherits three chromosomes rather than the normal two. For this reason, this disorder is sometimes called trisomy 21. Trisomy 21 is one situation that leads to Down Syndrome, however, there are other genetic situations that produce Down Syndrome. We will discuss Trisomy 21 this semester. Symptoms of Down Syndrome include distinct physical features, mental retardation, speech problems, and slow motor development. The risk of Down syndrome increases dramatically with maternal age. Genetic Counseling: 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. Genetic counseling is a communication process designed to help a couple to assess the likelihood of giving birth to a baby

with a hereditary disorder and to choose the best course of action in view of risks and family goals. The genetic counselor interviews the couple and prepares a pedigree, a picture of the family tree in which affected relatives are identified. The pedigree is used to estimate the likelihood that parents will have an abnormal child. Prenatal Diagnosis and Fetal Medicine: Prenatal diagnostic methods permit detection of problems before birth by utilizing certain medical procedures such as amniocentesis, chorionic villus sampling, ultrasound, and maternal blood analysis. Improvements in prenatal diagnosis have led to advances in fetal medicine; some problems can be treated before birth. Nevertheless, these techniques (except ultrasound and maternal blood analysis) frequently result in complications, the most common being premature labor and miscarriage. The goal of today’s genetic engineers is to map chromosomes and to correct hereditary defects with genetic repair or replacement. Amniocentesis A hollow needle is inserted through the abdominal wall to obtain a sample of the fluid in the uterus. Cells are examined for genetic defects. The procedure can be performed by 11 to 14 weeks after conception but safest after 15 weeks. Small risk of miscarriage1-2 weeks for test results Chorionic villus sampling A procedure used to answer genetic questions early in pregnancy (risk associated with limb deformities and risk increases with time). A hollow tube is inserted into the uterus through the abdominal wall or the vagina. A plug of tissue is removed from the end of one or more chorionic villus (hair like projections on the membrane surrounding the developing organism). Cells are examined for genetic defects. Chorionic villus sampling can be performed between 6 and 8 weeks with a 24-hour turn-around time for test results. The Alternative of Adoption Adoption is an alternative to having a biological child. 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. Most adopted children have happy childhoods and grow up to be well-adjusted adults.

Environmental Influences on Development: The child’s environment consists of many influences that combine to affect the course of development. The Family The family is a network of interdependent relationships. Parents and children are directly affected by each other. The behavior of one family member helps sustain a form of interaction in another that either promotes or undermines children’s well-being. 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. 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. Lower-SES parents value external characteristics (e.g. obedience and neatness) and are more restrictive in interactions with their children. Higher-SES parents value psychological traits (e.g. happiness and curiosity) and more often engage in verbal interaction with their children. SES is positively correlated with cognitive and language development and academic success. The Impact of Poverty 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. Poverty is more widespread among children than any other age group, a circumstance that is particularly worrisome because the earlier poverty begins and the longer it lasts, the more devastating are its effects on physical and mental health and school achievement. The constant stress of poverty weakens the family system. Parents experience many daily hassles and crises, which reduce their ability to effectively deal with the children. Poor housing and dangerous neighborhoods increase the stress levels of impoverished families. Homeless children suffer from developmental delays, emotional stress, health problems, school absenteeism, and poor academic performance. Neighborhoods Children are better adjusted socially and emotionally when their neighborhood experiences are more varied. Neighborhood resources have a greater impact on young people growing up in economically

disadvantaged than well-to-do neighborhoods. In low-income neighborhoods, after-school programs can be substituted for a lack of resources by providing enrichment activities. 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. Schools School is a formal institution designed to transmit knowledge and skills that children need to become productive members of society. Schools differ in the quality of their physical environments, educational philosophies, and social life. Regular contact between families and teachers supports children’s development. Towns and Cities Small towns have fewer cultural experiences available than cities. However, small towns offer greater community involvement and safer environments for children. Community life is especially undermined in high-rise urban housing projects. Cultural Values and Practices Cultures shape family interaction, school experiences, and community settings beyond the home. Independence, self-reliance, and the privacy of family life are central American values. America’s valuing of an autonomous family is one reason that the American public has been slow to endorse publicly supported benefits for all families, such as health insurance and high-quality child care. Some cultural traditions promote extended-family households, in which a parent and child live with one or more adult relatives. In collectivist societies, people define themselves as part of a group and stress group over individual goals. 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. Reference: Berk, L. E. (2004) Development through the lifespan. Allan and Bacon: Boston. Berk, L. E. (2010, 2016). Infants, Child, and Adolescents, Pearson: Boston