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Genetics & Prenatal Development Overview of Genetics • Chromosomes are long twisted strands of deoxyribonucleic acid (DNA) and are found in the nucleus of the cell • Humans have 23 pairs of chromosomes • DNA is the chemical basis of heredity and carries instructions • DNA code carried on each chromosome is arranged in thousands of segments called genes. • Genes are the basic unit of heredity Conception Conception • At conception, the genes carried on the 23 chromosomes contributed by your biological mother’s ovum were paired with the genes carried on the 23 chromosomes contributed by your biological father’s sperm, creating your unique genetic makeup. • Multiple gene pairs are involved in directing many complex features of development. Dominant and Recessive • Genotype—underlying genetic makeup • Phenotype—traits that are expressed/displayed • Dominant genes—will always be expressed if present – Traits such as freckles, dark eyes, dark hair, and dimples are referred to as dominant characteristics because they require only one member of a gene pair to be dominant for the trait to be displayed • Recessive genes—will expressed only if paired with an identical recessive gene. Will not be expressed if paired with a dominant gene. • We inherit from our biological parents a genetic potential, the expression of which can be influenced by environmental conditions. Characteristic Dominant Recessive Eye color Brown Grey, blue Hair Dark Light Curly Straight Hands Extra fingers 5 fingers Limb dwarfing Normal limbs Face Broad lips Thin lips Dimples No dimples Sex Linked Traits • The sex chromosomes, the 23rd pair of chromosomes, determine biological sex • In females, the 23rd pair of chromosomes is made up of two large X chromosomes. XX • In males, a large X chromosome and a smaller Y chromosome make up the 23rd pair. XY • For males, the smaller Y chromosome often does not contain a corresponding gene segment to match the one on the X chromosome. • This means that a male can display certain recessive characteristics as the result of having only one recessive gene carried on the X chromosome of his XY pair. • Traits determined by recessive genes on the X chromosomes are referred to as sex-linked Physical and Psychological Development Related • Physical development begins at conception • Physical maturity sets limits on psychological ability – visual system not fully functional at birth – language system not functional until much later • Prenatal environment can have lifetime influence on health and intellectual ability Prenatal and Childhood Development Prenatal Development • Prenatal defined as “before birth” • Prenatal stage begins at conception and ends with the birth of the child. • At conception, chromosomes from the biological mother and father combine to form a single cell—the fertilized egg, or zygote. • The prenatal stage has three distinct phases: 1. germinal period, 2. embryonic period, Prenatal Development • Conception—when a sperm penetrates the ovum • Zygote—a fertilized egg • Germinal period—first two weeks after conception • Embryonic period—weeks three through eight after conception • Fetal period—two months after conception until birth From Conception to Zygote Zygote • A newly fertilized egg • The first two weeks are a period of rapid cell division. • Attaches to the mother’s uterine wall • At the end of 14 days becomes a cluster of cells called an embryo. Embryo • Developing human from about 14 days until the end of the eighth week • Time of rapid growth and intensive cell differentiation • Most of the major organs are formed during this time. • Genes on the sex chromosomes and hormonal influences trigger the initial development of the sex organs • At the end of the eighth week the fetal period begins. Embryo • The embryo is protectively housed in the fluid-filled amniotic sac; the embryo’s lifeline is the umbilical cord. • Via the umbilical cord, the embryo receives nutrients, oxygen, and water and gets rid of carbon monoxide and other wastes Placenta • A cushion of cells in the mother by which the fetus receives oxygen and nutrition • Acts as a filter to screen out substances that could harm the fetus • The umbilical cord attaches the embryo to the placenta, a disk-shaped tissue on the mother’s uterine wall. • The placenta prevents the mother’s blood from mingling with that of the developing embryo, acting as a filter to prevent some, but not all, harmful substances that might be present in the mother’s blood from reaching the embryo Prenatal Development Fetal Period • The period between the beginning of the ninth week until birth 1. By the end of the third month, the fetus can move its arms, legs, mouth, and head 2. During the fourth month, the mother experiences quickening—she can feel the fetus moving. 3. By the fifth month, the fetus has distinct sleep–wake cycles and periods of activity. 4. During the sixth month, the fetus’s brain activity becomes similar to that of a newborn baby. 5. During the final two months, the fetus will Prenatal Development – 45 Days Prenatal Development – 2 months Prenatal Influences on Development • Nutrition • Anxiety • Mother’s general health • Maternal age • Teratogens—any agent that causes a birth defect (e.g., drugs, radiation, viruses) Teratogens • Substances that pass through the placenta’s screen and prevent the fetus from developing normally • Teratogens include: – Exposure to radiation – Diseases, such as rubella, syphilis, genital herpes, and AIDS – Toxic industrial chemicals, such as mercury and PCBs – Drugs taken by the mother, such as alcohol, nicotine, cocaine, and heroin Prenatal Development • Play “Teratogens and Their Effects on the Developing Brain and Mind” (12:44) Segment #12 from The Mind: Psychology Teaching Modules (2nd edition) Smoking and Birth Weight Fetal Alcohol Syndrome – cluster of defects occurring in infants born to mothers that drink heavily during pregnancy – leading cause of mental retardation – can be totally prevented by abstaining from alcohol during pregnancy Prenatal Brain Development • Play “The Effects of Hormones and the Environment on Brain Development” (6:50) Module #2 from The Brain: Teaching Modules (2nd edition)
"Genetics _ Prenatal Development"