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Chapter 2&3


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University of Toronto Mississauga
Elizabeth Johnson

Chapter 2: Heredity and The Environment Notes Genetic Influences on Development 1.Genetic disorders: for a full list of genetic disorders see Table 2-2 on pages 51-52 a) Why harmful alleles survive: • major reason - harmful alleles survive b/c they are not harmful in the heterozygous state - that is, when a person inherits both a normal and a recessive one • ex.: the cause of PKU is a recessive allele that fails to produce an enzyme necessary to metabolize the protein phenylalanine in milk. As long as a person also processes a normal allele,the PKU allele has no ill effects(this person is just a carrier of the recessive allele). The problems start only in infants who are homozygous for the recessive allele. • some harmful alleles may survive b/c they are actually beneficial in combination with a norma allele • ex.: people with only one sickle cell anemia allele have built-in resistance to malaria b) Down Syndrome(trisomy 21): • a form of chromosome abnormality,in which the person suffers disabling physical and mental development and is highly susceptible to such illnesses as leukemia,heart disorders,and respiratory infections with advances in the treatment of physical disorders(ex.pneumonia),the lifespans of people with Down syndrome has • greatly increased • the extra 21st chromosome most often comes from the mom,when her homologous pair of 21st chromosomes fail to separate during meiosis • infant’s intellectual growth begins to decline after about a year, thus, special therapy is needed • Down syndrome children are generally slow to learn to speak and often have difficulty articulating words and even producing complex sentences in adolescence c) Sex-chromosomal anomalies: • Turner syndrome - a form of abnormality of the sex chromosomes found in females,in which secondary sex characteristics develop only if female hormones are administered and in which abnormal formation of internal reproductive organs leads to permanent sterility • girls are born with only one X chromosome due to father’s sperm lack of X or Y chromosome • XO girls remain short,with stubby fingers,webbed necks,and unusually shaped mouths and ears • they usually have normal intelligence • Klinefelter’s syndrome - a form of chromosome abnormality,in which a male inherits an extra X sex chromosome, resulting in the XXY pattern,and has many feminine characteristics as well as language deficits,and sometimes,mental retardation • males are sterile and has cognitive problems • females with an extra X chromosome(triple-X) appear normal physically and have normal secondary sexual development,but their cognitive capabilities are affected(especially STM) • fragile X syndrome - a form of chromosome abnormality, more common in males than in females, in which an X chromosome is narrowed in some areas, causing it to be fragile and leading to a variety of physical,psychological,and social problems • some symptoms include: cleft palate,seizures,abnormal electroencephalograms(EEGs) and disorders of the eye • psychological and social problems include: anxiety,hyperactivity,attention deficits,abnormal communication 2. Prenatal Diagnostic Techniques: a) Commonly used tests: • amniocentesis - a technique for sampling and assessing fetal cells for indications of abnormalities in the developing fetus; performed by inserting a needle through the abdominal wall and into the amniotic sac and withdrawing a small amount of the amniotic fluid • chorionic villi sampling - a technique for sampling and assessing cells withdrawn from the chorionic villi, which are projections from the chorion that surrounds the amniotic sac; cells are withdrawn either through a tube inserted into the uterus through the vagina or through a needle inserted through the abdominal wall • alphafetoprotein assay (AFP) - a blood test performed prenatally to detect such problems as Down syndrome,the presence of multiple embryos,and defects of the CNS • ultrasound - a technique that uses sound waves to visualize deep body structures;commonly used to reveal the size and structure of the developing fetus b) Ethical and policy issues: • even a non-genetic test such as ultrasound is associated with ethical problems • ex. in countries where male children are preferred over females, ultrasound could lead to an increase in the rate for abortions of female fetuses • genetic tests raise troubling issues of ethics and policy in such areas as employment, personal insurance,and among people who oppose abortion Heredity - Environment Interactions 1.How the environment influences the expression of genes: • range of reaction - the notion that the human being’s genetic makeup establishes a range of possible developmental outcomes, within which environmental forces largely determine how the person actually develops • see Figure 2-7 on page 63 • when reaction range is extremely narrow,it’s said to show strong canalization • canalization - the genetic restriction of a phenotype to a small number of developmental outcomes, permitting environmental influences to play only a small role • some researchers argue that individual development is organized into multiple levels - genetic activity, neural activity, behaviour, and environment - all of which influence each other • another factor is the stage of the child’s development - both developmental stage and the environment determine the likelihood that a genetically based trait/characteristic will be influenced by environmental forces • ex. special PKU diet must begin immediately after birth b/c delays of even a few months can have devastating effects on the child’s intellectual development 2. How genetic makeup helps shape the environment: • the idea that genes can shape the environment is new and less commonly acknowledged • there are 3 ways in which people’s genetic makeup can influence their environments: 1) passive genetic-environmental interaction - the interactive environment created by parents with particular genetic predispositions who encourage the expression of these tendencies in their children • ex. well-educated parents may provide a home with books and stimulating conversation,thus enhancing their children’s inherited tendencies to be bright 2)evocative genetic-environmental interaction - the expression of the gene’s influence on the environment though an individual’s inherited tendencies to evoke certain environmental responses (social) • ex. babies with an inborn tendency to smile often will probably elicit more positive stimulation from others than will very serious-looking,unresponsive infants 3)active genetic-environmental interaction - a kind of interaction in which people’s genes encourage them to seek out experience compatible with their inherited tendencies • ex. in the process of niche picking, people search for, select, or build environments that are compatible with their predispositions (extroverts will seek the company of people) Hereditary, Environment, and Individual Differences • for methods of studying individual differences see lecture notes 1.Some individual differences and their contributions: a) Intellectual characteristics: • the closer the genetic links b/w 2 people the more similar their IQ score • identical twins are most similar in IQ scores (+ .86 correlation), least similar are cousins (+ .15 correlation) • differences in spatial and verbal abilities are more influenced by genetic factors than are differences in memory and perceptual speed • differences in creativity shows the least genetic influence • timing and rate of development seem to be influenced greatly by genes - identical twins show greater similarities than do fraternal twins • adoption studies also reveal significant genetic contributions b/c adopted identical twins’ intelligence correlates closely with their biological parents’ intelligence b) Temperament and personality: • temperament - the individual’s typical mode of response to the environment, including such things as activity level, emotional intensity,and attention span • a higher rate of developmental problems is found later life among children described by their mothers as difficult babies; 2 factors can be contributed to this: • a less malleable child is likely to find it harder to adapt to environmental demands and is more prone to stress and the toll it takes on emotional well-being • the child is more apt to elicit adverse reactions from other people,and thus,to suffer the psychological damage caused by social rejection • these children serve as targets for parental irritability,and stressed mothers are especially likely to withdraw affection • goodness to fit - a measure of the degree to which a child’s temperament is matched by her environment. The more effectively parents and others agents of socialization accept and adapt to the child’s unique temperament,the better this “fit” Chapter 3: Prenatal Development and Birth Notes Stages of Prenatal Development 1.The zygote: 1st 2 weeks of life • • zygote - the developing organism from the time of the union of the sperm and the egg to about the 2nd week of gestation; the period of the zygote is comprised of the implantation of the fertilized egg in the wall of the uterus 2. The embryo: • embryo - the developing organism b/w the 2nd and 8th weeks of gestation; this period comprises the differentiation of the major physiological structures and systems • during this time, the organism’s most important physiological structures and systems become differentiated • 3 crucial structures develop to protect and support the embryo: • amniotic sac - a membrane containing a watery fluid that encloses the embryo,protecting it from physical shocks and temperature changes • placenta - together with the umbilical cord serves to protect and sustain the life of the embryo • umbilical cord - tube containing blood vessels that carry blood back and forth b/w the baby and the mother • the placenta and umbilical cord do not permit direct exchange of blood • prenatal development is guided by 2 principles: • cephalocaudal - development begins in the area of the brain and proceeds downward proximal-distal - development starts in central areas and proceeds to more distant areas • • most miscarriages occur during this period 3.The fetus: • fetus - the developing organism from the 3rd month of gestation through delivery; development of bodily structures and systems become complete • rapid growth in muscular development and CNS five months - reflexes (hiccup) appear • • lanugo - a fine,soft hair that covers the fetus’ body from about the 5th month of gestation on • six months - eyes open and close • for complete overview of the stages of development see pages 88-89 • age of viability - the age of 22-26 weeks,by which point the fetus’ physical systems are well enough advanced that it has a chance of survival if born prematurely Risks in The Prenatal Environment • teratogen - an environmental agent that may cause developmental deviations in a growing human organism • other factors that could affect the baby - mother’s age, her diet, and her emotional state teratogens exert their effects in specific ways: • 1)A teratogen exerts its effects largely during critical periods. The organism is most vulnerable during the embryonic stage, however, each organ system has a different critical period. 2)Each teratogen exerts certain specific effects. 3)Either maternal or fetal genotypes may counteract a teratogen’s effects. Infants who develop defects do so b/c of their own genetic vulnerability. 4)The effects of one teratogen may intensify the effects of another. Ex.: nutritional deficiencies intensify the effects of drugs. 5Different teratogens may produce the same defect. 6)The longer a fetus is exposed to a particular teratogen and the greater the intensity of the teratogen’s effects, the more likely it’s that the fetus will be seriously harmed. 1.Environmental dangers: a) Legal and illegal drugs: • heavy use of Aspirin has been associated with low birthweight,lower IQ,and poor motor control • too much caffeine could cause miscarriage or low birthweight b) Nicotine and alcohol: smoking and drinking are associated with disturbances in placental functioning and with changes in maternal • physiology that lead to oxygen deprivation and,thus,to changes in the fetus’ brain • the rate of miscarriages is higher for mothers who smoke/drink • SIDS in more common in the offspring of mothers who smoke,drink,or take narcotic drugs • prenatal exposure to nicotine also has significant cognitive effects • passive smoking can contribute to low birthweight, and have an increased risk for variety of illnesses, such as pneumonia, bronchitis, laryngitis, and inner-ear infections • fetal alcohol syndrome (FAS) - a disorder exhibited by infants of alcoholic mothers and characterized by stunted growth,a number of physical and physiological abnormalities and,often, mental retardation • infants have a high incidence of facial,heart,and limb defects and they r 20% shorter than the average child • fetal alcohol spectrum disorder (FASD) - an umbrella term used to describe the range of effects associated with prenatal exposure to alcohol • the fetal damage from alcohol tends to be greatest in the last trimester c) Heroin,cocaine,and other drugs: • heroin/morphine addicted mother’s babies tend to be addicted as well • withdrawal symptoms in these infants include: irritability,minimal ability to regulate their state of arousal,trembling, shrill crying,rapid respiration,and hyperactivity • in some cases, symptoms can be severe enough to result in an infant’s death in the 1st few days of life cocaine is related to the following physical defects: bone,genital,urinary tract,kidney,eye and heart deformities, and • brain hemorrhages 2. Environmental toxins: • dangerous substances in everyday environment: radiation,lead,mercury,herbicides,pesticides,household cleaners,food additives and cosmetics • exposure to lead has been associated with prematurity and low birthweight,brain damage,physical defects and long- term problems in cognitive and intellectual functioning • father’s exposure to such toxins also has an effect on the baby 3.Medical interventions in pregnancy and childbirth: a) Some therapeutic disasters: • diethylstilbestrol (DES) - a synthetic hormone once prescribed to pregnant women to prevent miscarriages but discontinued when cancer and pre-cancerous conditions(predominantly in the reproductive organs) were detected in the children of such women • thalidomide - a drug once prescribed to relieve morning sickness in pregnant women but discontinued when found to cause serious malformations of the fetus most characteristic and most horrible deformity was something called phocomelia, in which limbs are missing and • the feet and hands are attached directly to the torso in such way that,to many. they looked like flippers 4. Maternal factors: a) Age and parity: • the chance of becoming pregnant declines steadily after age 27 • the chance of miscarriages and chromosomal abnormalities increase with age as well • however,the vast majority of older women have normal pregnancies and healthy babies • recent evidence suggests that older fathers may also contribute to poor birth outcomes • teenage mothers may have problems b/c their reproductive systems are immature,they are more likely to have an unhealthy personal habits,and they tend to live in environments characterized by high rates of disease and environmental pollutants b) Choice of diet: • dietary deficiencies are related to increased rates of miscarriage,stillbirth,and infant mortality • the specific form the damage takes depends on the age at which the maln
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