Invitation to the Life Spanby Kathleen Stassen Berger Chapter 2 – Genes and Prenatal Development PowerPoint Slidesdeveloped by Martin Wolfger and Michael James Ivy Tech Community College-Bloomington
The Beginning of Life • DNA (deoxyribonucleic acid): • Molecule that contains the chemical instructions for cells to manufacture various proteins • Promotes growth and sustains life • Chromosomes: • Molecules of DNA • DNA consists of 46 chromosomes arranged in 23 pairs
The Beginning of Life • Gametes: • Reproductive cells (sperm and ova) • Each gamete consists of 23 chromosomes. • Zygote: • Two gametes (sperm and ovum) combine and produce a new individual with 23 chromosomes from each parent. • Genes: • Specific sections of a chromosome that carry instructions via four chemicals. • Chemicals are organized in four pairs (AT, TA, CG, GC). • Each person has about 3 billion pairs.
The Human Genome • Genetic Diversity • Distinguishes each person • Allows the human species to adapt to pressures of the environment (e.g. climate changes, illnesses). • Genome: • The full set of genes that are the instructions to make an individual member of a certain species • Similarity between two people: 99.5% • Similarity between humans and chimpanzees: 98% • Similarity between humans and every other mammal: 90+%
Siblings and Twins • Sibling Similarities • Each sibling gets abut 10,000 genes from each parent. • Millions of variations and billions of combinations are possible. • Full siblings are not necessarily alike. • Monozygotic (identical) twins: • Originate from one zygote that splits apart very early in development. • Incomplete split results in conjoined twins. • Same genotype but slight variations in phenotype are possible due to environmental influences.
Siblings and Twins • Dizygotic (fraternal) twins • Result from fertilization of two separate ova by two separate sperm. • Dizygotic twins have half their genes in common and occur twice as often as monozygotic twins. • Incidence is genetic and varies by ethnicity and age.
Male and Female • Humans usually possess 46 chromosomes. • 44 autosomes and 2 sex chromosomes • Females: XX • Males: XY • Sex of offspring depends on whether the father’s Y sperm or X sperm fertilizes the ovum.
Chromosomal Abnormalities Down Syndrome (Trisomy-21) Three copies of chromosome 21 Specific facial characteristics (thick tongue, round face, slanted eyes) Hearing losses, heart abnormalities, muscle weakness, short stature Slow to develop language Accelerated aging (cataracts, dementia, certain forms of cancer common at age 40) Genetic Problems
Genetic Problems • Abnormalities of the Sex Chromosomes • Turner Syndrome (X only): • Unusually short, underdeveloped female organs, infertile • Slow to develop • Problems in spatial understanding • Klinefelter Syndrome (XXY): • Symptoms include learning problems and infertility • Boy’s penis does not grow during puberty and fat accumulates around the breast area • Sometimes not recognized until adulthood
Genetic Problems • Gene Disorders • Dominant Disorders • Half of the offspring of parents with a dominant disorder will have the disorder. • Most dominant disorders begin in adulthood (fatal dominant childhood conditions cannot be passed on). • Many dominant disorders have relatively mild or variable symptoms. • Tourette syndrome • Some who inherit the dominant gene exhibit uncontrollable tics and explosive outbursts • Most have milder, barely noticeable symptoms
Advising Prospective Parents • Genetic Counseling • Consultation and testing by trained professionals • Enables prospective parents to learn about their genetic heritage, including harmful conditions that may be passed on to their offspring • Ethical Guidelines • Test results are kept confidential • Decisions regarding sterilization, adoption, abortion, or carrying a pregnancy to term are made by the clients
Potential genetic counseling issues Prospective parents must base some decisions on odds Tests often reveal that more tests are needed False positives and false negatives True positives may cause additional stress Presenting the Facts
From Zygote to Newborn Three main periods of prenatal development • Germinal Period (first two weeks after conception): rapid cell division and beginning of cell differentiation • Embryonic Period (3rd through 8th week): basic forms of all body structures develop • Fetal Period (9th week until birth): fetus grows in size and matures in functioning
The Germinal Period • Zygote begins duplication and division within hours of conception • Development of the placenta • Organ that surrounds the developing embryo and is attached to the wall of the uterus • Sustains life via the umbilical chord (nourishes organism and carries waste products away) • Implantation (about 10 days after conception) • Developing organism burrows into the placenta that lines the uterus • Organism grows rapidly • Pregnancy can be detected due to new chemicals in the mother’s urine
The Embryonic Period Embryo • Developing human organism from about the 3rd through the 8th week after conception • Begins when the primitive streak appears down the middle of the cell mass • Primitive streak becomes the neural tube and later forms the brain and spine of the CNS • Head takes shape • Eyes, ears, nose, and mouth form • Heart begins to pulsate • Extremities develop and webbed fingers and toes separate
Fetus Developing human organism from the start of the 9th week after conception until birth Genitals form and sex hormones cause differences in fetal brain organization Cephalocaudal and proximodistal growth Heartbeat detectable via stethoscope All body parts and systems complete prenatal development Cortex is not fully mature at birth (e.g. prefrontal lobes) Brain at birth is far bigger than any other part of the baby The Fetal Period
Birth • Fetal brain signals the release of hormones to trigger the female’s uterine muscles • Labor begins • Average duration for firstborn babies: 12 hours • Quicker labor for later-born babies • Apgar scale • Quick assessment of newborn’s heart rate, breathing, muscle tone, color, and reflexes • Completed twice (1 minute and 5 minutes after birth) • Score of 0, 1, or 2 in each category • Desired score: 7 or above
Traditional and Modern Birthing Practices • Home births • Hospital births • Doula • Woman who helps with labor, delivery, breast-feeding, and newborn care • May be related to lower rate of cesarean sections
Medical Intervention • Infant mortality has decreased due to better medical care • 1900: 5% • Today: <1 in 200 • Childbirth has become safer for mothers • Death rate in poorest nations: 1 in 20 women • Excessive medical care also has disadvantages • Increase in unnecessary c-sections is associated with higher rate of low-birth weight babies
Low Birthweight • Low birthweight (LBW) • Less than 2,500 grams (5½ pounds) at birth • United States • Steady increase in LBW over the past 25 years • 8% of newborns are seriously underweight • More susceptible to teratogens, higher birth risks, lower survival rate • Very low birthweight (VLBW) • Under 1,500 grams (3 pounds, 5 ounces) at birth • Extremely low birthweight • Under 1,000 grams (2 pounds, 3 ounces) at birth
Genetic factors Maternal illness Exhaustion Infection Malnutrition Drug use Multiple births Causes of Low Birthweight
Mothers, Fathers, and a Good Start The Father’s Role • Supportive father helps mother stay healthy • Father can decrease or increase mother’s stress (affects fetus) • Most fathers are helpful to their pregnant wives • Two way street: Pregnant mothers should support, involve, and encourage fathers
Postpartum Depression • Sadness and inadequacy felt by 8-15% of new mothers in the days and weeks after giving birth • Symptoms range from baby blues to postpartum psychosis • Depressed mothers find baby care burdensome and may think about mistreating the infant • Paternal involvement can have beneficial effect • Some fathers are depressed themselves • Causes for Postpartum Depression vary
Bonding Parent-Infant Bond • The strong, loving connection that forms as parents hold, examine, and feed the newborn • Early skin-to-skin contact is not essential • Cross-fostering in monkeys • Newborns are removed from their mothers and raised by another female or male • Strong and beneficial relationship sometimes develops
Alcoholism • Alcoholism probably has a genetic basis • Genes can cause an overpowering addictive pull in some people • Environmental conditions can modify the genetic effects • Nature and nurture must combine to create an alcoholic • Fetal Alcohol Syndrome (FAS) • A cluster of birth defects that may occur in the child of a woman who drinks alcohol while pregnant • Includes abnormal facial characteristics, slow physical growth, and retarded mental development
Prenatal Teratogens • Substances and conditions that can impair prenatal development and result in birth defects or even death • Not all teratogens can be avoided • Structural abnormalities are obvious at birth • Behavioral teratogens • Affect the child’s developing brain • Can cause developmental retardation, hyperactivity, and learning disabilities • Effects do not become evident for months or years
Significant Factors • Timing of Exposure • Critical period: time when a body part develops • First two months for structural abnormalities • Often before woman knows she is pregnant • Time when most spontaneous abortions occur • Sensitive period: time when teratogens can interfere with recent growth