Child Development, 3/e by Robert Feldman Chapter 3 The Start of Life: Genetics and Prenatal Development Created by Barbara H. Bratsch

What is our basic genetic endowment, and how can human development go awry? How do the environment and genetics work together to determine human characteristics? Which human characteristics are significantly influenced by heredity? What happens during the prenatal stages of development? What are the threats to the fetal environment, and what can be done about them?

Genetics Our genetic code is stored in our genes. All genes are composed of DNA (deoxyribonucleic acid) that determines the nature of every cell in our bodies and how they will function. 46 Chromosomes are organized into 23 pairs of DNA portions A zygote is a new cell formed by fertilization Gametes are sex cells from the mother and father that form a new cell at conception

Genetics

Multiple Births Monozygotic twins are genetically identical and formed by one fertilized ovum that splits Dizygotic twins are formed when two separate ova are fertilized by two separate sperm at the same time

How are boys and girls made? Females are made by the 23rd pair of chromosomes that consist of XX ( an X chromosome from the mother and an X chromosome from the father) Males are made by the 23rd pair of chromosomes and consist of an XY (an X chromosome from the mother and a Y chromosome by the father

Making a Girl Making a Boy

Basics of Genetics Dominant trait – one trait expressed when two competing traits are expressed Recessive trait – a trait present in an organism but not expressed Genotype – the underlying combination of genetic information (not outwardly visible) Phenotype – an observable trait Homozygous - Similar genes for a given trait that are inherited from parents Heterozygous – Different forms of a gene for a given trait inherited from parents

Phenylketonuria (PKU) – an inherited disorder in which a child is unable to make use of phenylalanine, an essential amino acid present in proteins found in milk and other levels. If left untreated, PKU allows phenylalanine to build up to toxic levels and the result can be brain damage and mental retardation

Polygenic inheritance Gregor Mendel pioneered experiments on pea plants that provided the foundation for the study of genetics Polygenic inheritance a combination of multiple gene pairs is responsible for production of a particular trait X-linked genes are recessive and located only on the X chromosome. Hemophilia is produced by X-linked genes

The Human Genome Completed in early 2001, the mapping of the specific sequence of genes on each chromosome was one of the most important moments in the history of genetics Behavioral Genetics studies the effects of heredity on behavior

Inherited and genetic disorders include: PKU Down syndrome Fragile X syndrome Sickle-cell anemia Tay-Sachs disease Klinefelter’s syndrome

Genetic Counseling focuses on helping people deal with issues related to inherited disorders Prenatal testing includes an amniocentesis in which fetal cells are drawn out of the amniotic sac before a child is born Chorionic villus sampling (CVS) can be performed even earlier at 8-11 weeks and involves sampling of hairlike materials that surround an embryo Ultrasound sonography – high frequency sound waves are used to produce an image of the unborn child. This is less risky and invasive than amniocentesis or CVS

Heredity Vs. Environment Multifactorial transmission states that many traits are a combination of both genetic and environmental factors

How to Answer the Nature-Nurture Riddle Animal studies – breeding genetically similar animals and determining various environmental influences Human studies – studies of monozygotic and dizygotic twins have produced data around genetic similarities, dissimilarities and environment

Genetics and IQ Genetics plays a significant role in intelligence The closer the genetic link between two individuals, the greater the correspondence of their overall IQ scores

Genetics, Environment, and Personality These traits are among the personality factors that are related most closely to genetic factors

Genetics, Environment, and Psychological Disorders

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

Can Genes Influence the Environment? Active genotype-environment effects – Situations in which children focus on aspects of their environment that are most congruent with their genetically determined abilities Passive genotype-environment effects – Situations in which parents’ genes are associated with the environment in which children are raised Evocative genotype-environment effects – Situations in which a child’s genes elicit a particular type of environment

Prenatal Growth and Change Fertilization, or conception, is the joining of sperm and ovum to create the single-cell zygote Female and Male Sex Organs

Giving Nature a Boost Infertility – inability to conceive after 12-18 months of trying to become pregnant Artificial insemination – fertilization process in which a man’s sperm is placed directly in a woman’s vagina by a physician In vitro fertilization (IVF) – a procedure in which a woman’s ova are removed from her ovaries and a man’s sperm are used to fertilize the ova in the lab Surrogate mother is a woman who agrees to carry a child to term if the mother who provides the donor eggs is unable to conceive

Stages of Prenatal Development: The Onset of Development Germinal - Fertilization to 2 weeks Embryonic - 2 weeks to 8 weeks Fetal stage - 8 weeks to birth

voluntary termination of a pregnancy Miscarriage spontaneous abortion Abortion voluntary termination of a pregnancy

Threats to Development Teratogen environmental agent such as a drug, chemical, virus, or other factor that produces a birth defect

Threats to Development Mother’s diet Mother’s age Mother’s prenatal support Mother’s illness Mother’s drug use Mother’s use of alcohol, tobacco, and caffeine Father factors