3Chromosomes and GenesGenetics - the field of biology that studies heredityFundamental in the transmission of physical traitsAlso plays a role in psychological traitsChromosomes – Rod-shaped structures composed of genes that are found within the nuclei of cellsGene – The basic unit of heredity. Composed of DNAPolygenic – Resulting from many genesDeoxyribonucleic Acid (DNA) – Genetic material that takes the form of a double helix composed of phosphates, sugars and bases.
4Identical and Fraternal Twins Monozygotic (MZ)- Zygote divides into two cells that separate so that eachdevelops into an individual with the same genetic makeup.Dizygotic (DZ)- Two ova are produced in the same month, each fertilized by a different sperm cell.Ovulation- As women reach end of childbearing years, ovulation becomes less regular.-Results in months when more than one ovum is releasedDZ twins run in families;Chances of a woman bearing twins increases if the woman was a twin, her mother was a twin, or if she has previously borne twins
5Chromosomal and Genetic Abnormalities Down syndromeCaused by an extra chromosome of the 21st pair, resulting in 47 chromosomesCharacteristic features-rounded face-protruding tongue-broad, flat nose-sloping fold of skin over the inner corners of the eyesShow deficits in cognitive development and motor developmentUsually die from cardiovascular problems by middle age, although modern medicine has extended life appreciably, the probability of having a child with Down’s syndrome increases with the age of the parents
6Genetic Counseling and Prenatal Testing Genetic counselors compile information about a couple’s genetic heritage to explore if their children will have a genetic abnormality.Couples with likelihood of passing on genetic abnormality tend to adopt or not have children of their own.Prenatal testing can indicate if the embryo or fetus is carrying genetic abnormalities.
7Amniocentesis Performed on mother 14-16 weeks after conception Syringe withdraws fluid from the amniotic sac; contains cells sloughed off by fetusCells separated, grown in culture, and examined for genetic and chromosomal abnormalitiesRoutine for women over 35 to detect for Down syndrome; other chromosomal abnormalities increase dramatically as women approach 40Amniocentesis carries some risk of miscarriage.Amniocentesis - a procedure for drawing and examining fetal cells sloughed off into amniotic fluid to determine the presence of various disordersHealth professionals would not conduct it just to learn the sex of the childMiscarriage - the expulsion of an embryo or fetus before it can sustain life on its own, most often due to defective development
8Chorionic Villus Sampling Carried out between 9th and 12th week of pregnancySyringe inserted through vagina into uterus to suck out threadlike projections (villi) from the outer membrane that covers the amniotic sac and fetusResults available in daysCVS slightly greater risk than amniocentesis of miscarriage; both increase the risk of miscarriage
9UltrasoundSound waves that are too high in frequency to be heard by human ear obtain information about the fetusUltrasound waves are reflected by the fetus; computer uses the information to generate a picture of the fetusPicture is termed a sonogramUsed to guide the syringe in amniocentesis and CVS by determining the position of the fetusUsed to track growth of fetus, detect multiple pregnancies, detect structural abnormalities
10Blood TestsUsed to identify sickle-cell anemia, Tay-Sachs disease, and cystic fibrosisAlpha-fetoprotein (AFP) used to detect neural tube defects such as spina bifida and chromosomal abnormalitiesNeural tube defects cause elevation in the AFP level in the mother’s bloodElevated AFP levels related to increased risk of fetal death
12Heredity and Environment Inheritance, nutrition, learning, exercise, accident, and illness contribute to development of traitsGenotypes-Set of traits we inherit from our parentsPhenotypes-Actual set of traits-Both genetic and environmental influencesGenotype the genetic form or constitution of a person as determined by heredityPhenotype the actual form or constitution of a person as determined by heredity and environmental factors
13Kinship StudiesThe more closely people are related, more genes they have in commonParents and children have 50% genetic overlapSiblings have 50% genetic overlapAunts, uncles have 25% overlap with nieces and nephews; grandparents, 25% overlap with grandchildrenFirst cousins have 12.5% overlap
14Twin Studies Monozygotic (MZ) twins share 100% of genes -MZ twins resemble each other more closely than DZ twins on a number of physical and psychological traits.-MZ twins more likely to look alike and be similar in height-MZ twins more likely to share autism, depression, schizophrenia, and vulnerability to alcoholismDizygotic (DZ) twins share 50% of genes; same as other siblingsIf MZ twins show greater similarity on some trait or behavior than DZ twins do, a genetic basis for the trait or behavior is indicatedMZ twins resemble one another more strongly than DZ twins in intelligence and personality traits.The MZ twins reared apart are about as similar as MZ twins reared together on measures of intelligence, personality, temperament, occupational and leisure-time interests, and social attitudes.
15Adoption StudiesChildren that are separated from their natural parents at an early age and reared by adoptive parents provide special opportunities for sorting out nature and nurture.When children who are reared by adoptive parents are nonetheless more similar to their natural parents in a trait, a powerful argument is made for a genetic role in the appearance of that trait.Examples: Psychological disorders, addiction
17Conception Conception refers to the union of an ovum and a sperm cell. OvaWomen born with all the ova they will ever have, about 400,000Released from ovarian follicle and enter fallopian tube; 3-4 days later, egg propelled by small, hairlike structures called cilia, and perhaps, by contractions in the wall of the tubeIf egg not fertilized, discharged through the uterus and vagina, along with endometrium that had formed to support an embryo, in the menstrual flow; during reproductive years, about 400 ova will ripen and be released
18Conception (cont’d)Ova are larger than sperm, barely visible to the eyeSperm cells develop through stages; sperm with Y sex chromosomes swim faster than sperm with X sex chromosomes.Male fetuses suffer a higher rate of miscarriage than females, often during the first month of pregnancy.150 million sperm ejaculated, only 1 in 1,000 can approach an ovumThey each begin with 46 chromosomes, but after meiosis, each sperm has 23 chromosomes, half with X sex chromosomes and half with Y
19Infertility Infertility problems with men - Low sperm count (most common)- Lack of sperm- Genetic factors- Environmental poisons- Diabetes- Sexually transmitted infections- Overheating of the testes- Pressure (e.g., bike seats)- Aging- Certain prescription and illicit drugsApproximately one American couple in six or seven has fertility problemsSometimes the sperm count is adequate, but other factors such as prostate or hormonal problems deform sperm or deprive them of their motility
20Infertility (cont’d) Infertility problems with women - Irregular ovulation, lack of ovulation- Irregularities among the hormones that governovulation, stress, and malnutrition- Pelvic inflammatory disorder (PID)-infection that scars the fallopian tubes and other organs,impeding the passage of sperm-Endometriosis-can obstruct the fallopian tubes
21Infertility Options Artificial insemination -Sperm is collected and quick-frozen-Sperm then injected into woman’s uterus at time of ovulation;addresses low sperm count as well as low sperm motility-Can be used for a woman to get pregnant who does not have a partnerIn vitro fertilization-Ripened ova are surgically removed from the mother andplaced in laboratory dish; father’s sperm also placed in dish-One or more ova fertilized and injected into mother’s uterus to become implanted-Used when fallopian tubes are blocked or father has low sperm motility-A donor can be used
22Infertility Options (cont’d) Donor IVF-Mother does not produce ova-Ovum from another woman is fertilized and injected into theuterus of the mother-to-beSurrogate mothers-Mothers who bring baby to term for other women who areinfertile-Can be artificially inseminated by partner of infertile womanAdoption-Another way for people to obtain children that results in theformation of loving new familiesClearly, a baby can’t grow in a test tube. “Test-tube” babies are conceived in a laboratory dish and embryos are implanted into the mother’s uterus for gestation.
23Preimplantation Genetic Diagnosis (PGD) Reliable method for selecting the sex of the child prior to implantationOva are fertilized in vitroAfter a few days of cell division, cell is extracted from eachSex chromosomal structure of the cell is examined microscopically to determine its sexEmbryos of desired sex are implanted in the woman’s uterus
25Prenatal DevelopmentNormal gestation period 280 days; from date of fertilization 266 daysDivided into three periods1. Germinal stage (Weeks 0 - 2)2. Embryonic stage (Weeks 3 - 8)3. Fetal stage (Weeks 9 - Birth)
26The Germinal Period First two weeks after conception Creation of the fertilized egg (the zygote)Cell divisionImplantation -- the attachment of the zygote to the uterine walltakes place about 10 to 14 days after conception
27The Embryonic Period Occurs from two to eight weeks after conception Rate of cell differentiation intensifiesEvery body part eventually developsNeural tubeOrganogenesis -- the process of organ formation during the first two months of prenatal developmentorgans are especially vulnerable to environmental influences
28The Fetal PeriodFetal period begins two months after conception (normal gestation is weeks)Three months after conception -- fetus is about 3 inches long; weighs about 3 ouncesBy the end of the fifth month, the fetus is about 12 inches long and weighs close to a poundVernixLanugoAt birth, the average American baby weighs 7½ pounds and is about 20 inches long
29Three TrimestersThe germinal and embryonic periods occur in the first trimesterThe fetal period begins toward the end of the first trimester and continues through the second and third trimestersAge of Viability (the chances of surviving outside the womb) occurs at the beginning of the third trimesterAbout weeks after conception
30Environmental Influences on Prenatal Development Maternal malnutrition effects-low birth weight-prematurity-retardation of brain development-cognitive deficiencies-behavioral problems-cardiovascular diseaseFetal malnutrition can sometimes be overcome by a supportive, care-giving environment.Supplementing diets of pregnant women shows positive effects on motor development of infants.Maternal obesity linked with higher risk of stillbirthEnriched day-care programs enhance intellectual and social skills by 5 years of age
31Environmental Influences on Prenatal Development (cont’d) Women should gain between pounds-Overweight women may gain less-Slender women may gain moreTeratogens-Environmental agents can harm the embryo or fetus-Includes drugs taken by mother, lead, mercuryPathogens-Disease-causing organisms-Bacteria and viruses
32Environmental Influences on Prenatal Development (cont’d) Critical periods refer to the times when organs are developing.Particular teratogens at a particular time can be harmful to the fetus.Sexually transmitted infections such as syphilis and HIV/AIDS can affect the development of the fetus.-Routine blood tests are given early in pregnancy to diagnose syphilis
33Drugs Taken by the Parents (cont’d) AlcoholHeavy alcohol consumption during pregnancy can result in fetal alcohol syndrome (FAS).FAS babies-often smaller, with smaller brains-facial features include widely spaced eyes, underdeveloped upper jaw, flattened nosePsychological characteristics appear to reflect dysfunction of the brain.Maladaptive behaviors such as poor judgment, distractibility, and difficulty perceiving social cues are common.
34Drugs Taken by the Parents (cont’d) CaffeineResearch regarding caffeine consumption is inconsistent-Several studies have found that pregnant women who take in a good deal of caffeine are more likely than nonusers to have a miscarriage or a low-birth-weight baby.
35Drugs Taken by the Parents (cont’d) CigarettesConsist of nicotine, carbon monoxide, and hydrocarbons (tars)-Nicotine and carbon monoxide pass through placenta and reach the fetus-Nicotine stimulates the fetus; long-term effects unknown-Carbon monoxide decreases amount of oxygen available to the fetus-Connected with impaired motor development academic delays, learning disabilities, mental retardation, and hyperactivitySmokers’ babies likely to be smaller than those of nonsmokers-Babies of smokers more likely to be stillborn or todie soon after birthMen who smoke are more likely to produce abnormal sperm.-Babies of fathers who smoke have higher rates of birth defects, infant mortality, lower birth weights, and cardiovascular problems.
36Parents’ Age Older fathers more likely to produce abnormal sperm 20’s ideal age for women to bear childrenTeenage pregnancy can result in higher incidence of infant mortality and low birth weight.Stillborn or preterm babies increase as age of mother increases; adequate prenatal care decreases this likelihood even for first-time older mothers.