Prenatal Development Module 45 Overview of Genetics Chromosomes

Prenatal Development Module 45

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.

Just because a trait is Recessive doesn’t mean it’s not common.

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, 3. fetal 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 • Zygote’s inner cells become the Embryo • 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 • Zygote’s outer cells become the 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

Prenatal Development – 45 Days

Prenatal Development – 2 months

• 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 double in weight.

See the changes that occur in prenatal development in this quick video

Prenatal Factors that Influence 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, lead and PCBs – Drugs taken by the mother, such as alcohol, nicotine, cocaine, and heroin

Smoking and Birth Weight

Fetal Alcohol Syndrome – cluster of defects occurring in infants born to mothers that drink heavily during pregnancy – leading cause of intellectual disabilities – Epigenetic Effect – alcohol alters the chemical markers on DNA that switch certain genes on or off. – can be totally prevented by abstaining from alcohol during pregnancy

Physical & 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