Child Development Chapter 2
Child Development Chapter 2 PSYC 333
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One Day of Notes
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Date Created: 09/12/14
Chapter 2 Hereditary Influences on Development 0 Genotype the genetic endowment that an individual inherits o The genes that one inherits 0 the ways in which a person39s genotype is expressed in cbseryibecrmea urable characteristics Most complex human characteristics are the result of a long and involved interplay between the forces of nature heredity and nurture environment Principles of Hereditary Transmission 0 Conception the moment of fertilization when a sperm penetrates an ovum forming a zygote The Genetic Material 0 Zygote a single cell formed at conception from the union of a sperm and an ovum o Contains the biochemical material for the zygote s development from a single cell into a complex human being 0 Chromosome a threadlike structure made up of genes o In humans there are 46 chromosomes in the nucleus of each body cell 23 from mom and 23 from dad o Contains genes o Come in matching pairs I Each member of a pair corresponds to the other in size shape and the hereditary function it serves 0 J hereditary blueprints for development that are transmitted unchanged from generation to generation o Function in pairs o Stretches of DNA 0 E long doube stranded molecules that make up chromosomes o Can replicate itself I The rungs in the latter split itself in the middle with the rest of the remaining half of the molecule to guide the replication of its missing parts 0 This is what makes it possible for a onecelled zygote to develop into a human being Growth of the Zygote and Production of Body Cells 0 Mitosis the process in which a cell duplicated its chromosomes and then divides into two genetically identical daughter cells 0 Zygote dlVldeS lnt0 2 Cells then 4 8 26 etC JUST 0 21 l 6 6 before each division the cell duplicates its 46 PAGE 47 chromosomes and move in opposite directions o Mitosis continues throughout life generating new cells that enable growth and replacing old ones that are damaged The Germ or sex Cells Production of Gametes through Meiosis Human beings have germ cells that serve one special function to produce gametes 0 Meiosis the process by which a germ cell divides producing gametes that each contain half of the parent ce s original complement of chromosomes o In humans the products of meiosis contain 23 chromosomes o Germ cell first duplicates its 46 chromosomes before crossingover 0 Crossingover a process in which genetic material is exchanged between pairs of chromosomes during meiosis o Adjacent duplicated chromosomes cross and break at one or more points along their length exchanging segments of genetic material I This transfer of genes creates new and unique hereditary combinations FIGURE 22 ON PAGE 48 ILLUSTRATES MEIOSIS Hereditary Uniqueness Meiosis makes us genetically unique 0 Independent assortment the principle that each pair of chromosomes segregates independently of all other chromosome pairs during meiosis o Many different combinations of chromosomes could result from the meiosis of a single germ cell I Mom and dad can produce 8 million genetic combinations in his sperm or her ova o The crossing over process alters the genetic composition of chromosomes and increases the number of possible variations in an individual s gametes Multiple Births 0 Monozygotic identical twins twins who develop from a sir1ge zygote that later divides to form two geenetisaJyiolentic Jin9livis2ya o Show very similar developmental processes 0 Dizygotic fraternal twins twins that result when a mother releases tIIC ova at roughly the same time and each is fertilized by a djfferer1t sperm producing two zygotes that are genetically different Male or Female Chromosomal portraits or karyotypes relate to autosomes Sex is determined by the 23quotquot pair of chromosomes 0 Autosomes the 22 pairs of human chromosomes that are identical in males and females 0 X Chromosome the longer of the two sex chromosomes o Normal females have two X chromosomes whereas normal males have only one 0 Y chromosome the shorter of the two sex chromosomes o Normal males only have one Y chromosome whereas females have none Fathers determine the sex of their children So a child s sex is determined by whether an Xbearing or Y bearing sperm fertilizes the ova What Do Genes Do How do genes influence development and a person39s phenotypic characteristics At the most basic biochemical level genes promote development through the production of amino acids which form enzymes and other proteins that are necessary for the formation and functioning of new cells Genes also guide cell differentiation making some cells part of the brain and central nervous system and others elsewhere Genes influence and are influenced by the biochemical environment surrounding them during development Environmental factors clearly influence how genes function Genes do not simply quotcode for human characteristics but that they interact with TABLE 21 0N PAGE 51 the environment at many levels to produce proteins that eventually influence human characteristics How Are Genes Expressed Four main patterns of genetic expression simple dominantrecessive codominance sexlinked inheritance and polygenic inheritance SIMPLE DOMINANTRECESSIVE INHERITANCE 0 e alternative forms of a gene that can appear at a particular site on a chromosome 0 Simple dominantrecessive inheritance a pattern of inheritance in which one allele dominates another so that only its phenotype is expressed o Mende s pea study through cross breeding 0 Dominant allele a relatively powerful gene that is expressed phenotypically and masks the effect of a less powerful genes 0 Recessive allele a less powerful gene that is not expressed phenotypically when paired with a dominant allele 0 Homozygous having inherited two alleles from an attribute that are identical in their effects 0 Heterozygous having inherited two alleles for an attribute that have different effects 0 Carrier a heterozygous individual who displays no sign of a recessive allele in his or her own phenotype but can pass this gene to offspring CODOMINANCE 0 Codominance condition in which two heterozygous but equally powerful alleles produce a phenotype in which both genes are fully and equally expressed o The phenotype they produce is a compromise between two genes o Blood type AB o Sicklecell anemia a genetic red blood disease that causes red blood cells to assume an unusual sickle shape and to become inefficient at distributing oxygen SEX LINKED INHERITANCE Some traits are called sex inked characteristics because they are determined by genes located on the sex chromosomes 0 Sex inked characteristic an attribute determined by a recessive gene that appears on the X chromosome o More likely to characterize males I Redgreen colorblindness I Hemophilia muscular dystrophy degeneration of the optic nerve and certain forms of deafness and night blindness POLYGENIC INHERITANCE Most important human characteristics are influenced by many pairs of alleles called polygenic traits 0 Polygenic trait a characteristic that is influenced by the action of many genes rather than a single pair o Height weight intelligence skin color temperament and susceptibility to cancer I NOT eitheror possibilities such as eye color I Instead the observable traits follow a pattern of continuous variation with most people having traits in the middle of a distribution bell curved Hereditary Disorders 0 Congenital defect a problem that is present at birth such FIGURE 23 ON PAGE 55 defects may stem from genetic and prenatal influences or from complications of the birth process Chromosomal Abnormalities When a germ cell divides during meiosis the distribution of the 46 chromosomes may become uneven One of the resulting gametes may have too many chromosomes and the other too few Abnormalities of the Sex Chromosomes Many chromosomal abnormalities involved the 23quotquot pair the sex chromosomes FEMALE ABNORMALITIES TABLE 22 ON PAGE 57 DESCRIBES XO Tumeps Syndrome A SEX Cquot39R quotquot 5 quotquotE o xxx xxxx or xxxxx Poy X or quotsuperfemale ABNORMALITIES Syndrome MALE ABNORMALITIES 0 XXY or XXXY Kinefeter s syndrome 0 XYY XYYY or XYYYY Supermale syndrome Abnormalities of the Autosomes Several hereditary abnormalities are attributable to the autosomes the 22 pairs of chromosomes that are similar in males and females The most common type occurs when an abnormal sperm or ovum carrying an extra chromosome combines with a normal gamete to form a zygote that has 47 chromosomes The extra chromosome appears along with one of the 22 pairs of autosomes to yield three chromosomes of that type or a trisomy 0 Down syndrome a chromosomal abnormality also known as trisomy21 caused by the presence of an extra 21 chromosome o People with this syndrome have a distinctive physical appearance and are moderately to severely retarded o Though intellectually impaired these children reach many of the same developmental milestones as normal children but at a slower pace Genetic Abnormalities These problems will not appear unless both parents carry the harmful allele and the child inherits this particular gene from each parent The exceptions to this rule are sexlinked defects that a male child will display if the recessive alleles for these traits appear on his X chromosome that he inherited from his mother A dominant genetic disorder is Huntington39s disease 0 Mutation a change in the chemical structure or arrangement of one or more genes that has the effect of producing a new phenotype o Can be induced by environment as well o Any mutation that is induced by stressors present in the natural environment may provide an quotadaptive advantage I Sicklecell anemia developed in Africa where malaria was is widespread This makes those with the disease more resistant to malarial infection and more likely to survive TABLE 23 ON PAGE 58 DESCRIBES MAJOR HEREITARY DISEASES Predicting Detecting and Treating Hereditary Disorders Predicting Hereditary Disorders 0 Genetic counseling a service designed to inform prospective parents about genetic diseases and to help them determine the likelihood that they would transmit such disorders to their children o Prediction of both chromosomal abnormalities and genetic abnormalities o Begin by obtaining a complete family history pedigree to identify relatives affected by hereditary disorders 0 FragileX syndrome abnormality of the X chromosome caused by a defective gene and associated with mild to severe mental retardation particularly when the defective gene is passed from mother to child Detecting Hereditary Disorders 0 Amniocentesis a method of extracting amniotic fluid from a pregnant woman so that fetal body cells within the fluid can be tested for chromosomal abnormalities and other genetic defects o Usually done on women over the age of 35 o Not easily performed before the 11 to 14 week of pregnancy when amniotic fluid becomes sufficiently plentiful to withdraw for analysis 0 Chorionic villus sampling CVS an alternative to amniocentesis in which fetal cells are extracted from the chorion for prenatal tests o CVS can be performed earlier in pregnancy than is possible with amniocentesis o Can use a catheter or a needle inserted through the abdomen into a membrane called the chorion that surrounds the fetus 0 Ultrasound method of detecting gross physical abnormalities by scanning the womb with sound waves thereby producing a visual outline of the fetus Treating Hereditary Disorders 0 Phenylketonuria PKU a genetic disease in which the child is unable to metabolize phenylalanine o If left untreated it soon causes hyperactivity and mental retardation o Attacks the nervous system o Newborn children are now routinely screened for PKU and affected children are placed on a lowphenylalanine diet Today many devastating effects of other hereditary abnormalities can be minimized or controlled 0 Germline gene therapy a procedure not yet perfected or approved for use with humans in which harmful genes would be repaired or replaced with healthy ones thereby permanently correcting a genetic defect Hereditary Influences on Behavior To what extent does heredity affect such characteristics as intelligence personality or mental health Behavioral Genetics Behavioral genetics the scientific study of how genotype interacts with environment to determine behavioral attributes such as intelligence personality and mental health Methods of Studying Hereditary Influences Use selective breeding and family studies Each approach attempts to specify the heritability of various attributes the amount of variation in a trait or a class of behavior within a specific population that is attributable to hereditary factors 0 Heritability the amount of variability in a trait that is attributable to hereditary factors Selective Breeding 0 Selective breeding experiment a method of studying genetic influences by determining whether traits can be bred in animals through selective mating Family Studies People who live together are compared to see how similar they are on one or more attributes If the attributes in question are heritable then the similarity between any two pairs of individuals who live in the same environment should increase as a function of their kinship 0 Kinship the extent to which two individuals have genes in common 0 Twin design a study in which sets of twins that differ in zygosity kinship are compared to determine the heritability of an attribute o Are pairs of identical twins reared together more similar to each other on various attributes than pairs of fraternal twins reared together 0 Adoption design study in which adoptees are compared with their biological relatives and their adoptive relatives to estimate the heritability of an attribute or attributes o Are asopted children similar to their biological parents whose genes they share or are they similar to their adoptive parents whose environment they share Family studies also help to estimate the extent to which various abilities and behaviors are influenced by the environment Estimating the Contribution of Genes and Environment Calculations to determine whether a trait is genetically influences and estimate the degree to which heredity and environment account for individual differences in that trait 0 Concordance rate the percentage of cases in which a particular attribute is present for one member of a twin pair if it is present for the other Gene Influences 0 Heritability coefficient a numerical estimate ranging from 00 to 100 of the amount of variation in an attribute that is due to hereditary factors 0 Nonshared environmental influence NSE an environmental influence that people living together do not share that should make these individuals different from one another o Experiences unique to the individual 0 Shared environmental influence SE an environmental influence that people living together share that should make these individuals similar to one another o Experiences that individuals living in the same home environment share and that conspire to make them similar to each other The term heritable is not a synonym for inherited and heritability estimates which vary widely across populations and environments can tell us nothing about the development of individuals Hereditary Influences on Intellectual Performance Might genes be more important early in life whereas differences in our home and school experiences increasingly account for the variations we show in intellectual performance as we get older Hereditary Contributions to Personality Psychologists have typically assumed that the relatively stable habits and traits that make up our personalities are shaped by our environments however family studies and other longitudinal projects reveal that many core dimensions of personality and genetically influenced 0 Introversionextroversion the opposite poles of a personality dimension o Introverts are shy anxious around others and tend to withdraw from social situations o Extroverts are highly sociable and enjoy being with others 0 Empathetic concern a measure of the extent to which an individual recognizes the needs of others and is concerned about their welfare How much genetic influence To what extent are our personalities influenced by the genes we have inherited Which aspects of Environment Influence personality The aspects of environment that contribute most heavily to personality are nonshared environmental influences influences that make individuals different from one another Parents treat sons differently than daughters oldest children different than youngest children etc Measuring the Effects of Nonshared Environment Ask pairs of adolescent siblings whether they have been treated differently by parents and teachers or have experienced other important differences in their lives differences in popularity with peers Do Siblings Have Different Experiences Because They Have Different Genes We have amble reason to believe that our highly individualized unique environments are not entirely due to our having inherited different genes Hereditary Contributions to Behavior Disorders and Mental Illness 0 Schizophrenia a serious form of mental illness characterized by disturbances in logical thinking emotional expression and interpersonal behavior o Emerges in late adolescence or early adulthood o Children who have a biological parent who is schizophrenic are at an increased risk of becoming schizophrenic even if they are adopted by another family early in life I Strongly genetically influenced 0 Bipolar disorder a psychological disorder characterized by extreme fluctuations in mood 0 Neurotic disorder an irrational pattern of thinking or behavior that a person may use to contend with stress or to avoid anxiety Theories of Heredity and Environment Interactions in Development Both heredity and environment contribute importantly to development and that the often extreme positions taken by hereditarians and environmentalists in the past are greatly oversimplified The Canalization Principle Refering to cases where genes limit or restrict development to a small number of outcomes 0 Canalization genetic restriction of phenotype to a small number of developmental outcomes o A highly canalized attribute is one for which genes channel development along predetermined pathways so the environment has little effect on the phenotype that emerges Illustrates that there are multiple pathways along which an individual might develop either genes or environment may limit the extent to which the other factor can influence development and nature and nurture combine to determine pathways The Range of Reaction Principle 0 Range ofreaction principle the idea that genotype sets limits on the range of possible phenotypes that a person might display in response to different environments GenotypeEnvironment Correlations Passive Genotype Environment Correlations The notion that the rearing environments that biological parents provide are influenced by the parents own genes and hence are correlated with the child39s own genotype Evocative Genotype Environmental Correlations The notion that our heritable attributes affect others behavior toward us and thus influence that social environment in which development takes place Active Genotype Environmental Correlations The notion that our genotypes affect the types of environments that we prefer and seek out How Do GenotypeEnvironmental Correlations Influence Development The relative importance of active passive and evocative gene influences changes over the course of childhood A person39s genetically influenced attributes and patterns of behavior may influence the ways other people react to him or her in life Separated Identical Twins Still show some similarities yet differ Twins could be expected to differ for which their rearing environments are so dissimilar as to prevent them from ever establishing comparable niches Contributions and Criticisms of the Behavioral Genetics Approach 1 People with different genotypes are likely to evoke different responses from others and to select different environmental niches for themselves 2 The responses they evoke and the niches they select depend to no small extent on the particular individuals settings and circumstances they encounter Genotypes and environments interact to produce developmental change and variations in developmental outcomes The Ethological and Evolutionary Viewpoints 0 Ethology the study of the bioevolutionary basis of behavior and development with a focus on survival of the individual Assumptions of Classical Ethology 0 Natural selection an evolutionary process proposed by Charles Darwin stating that individuals with characteristics that promote adaption to the environment will survive reproduce and pass these adaptive characteristics to offspring those lacking these adaptive characteristics will eventually die out Ethology and Human Development 0 Sensitive period the period of time that is optimal for the development of particular capacities or behaviors and in which the individual is particularly sensitive to environmental influences that would foster these attributes Modern Evolutionary Theory 0 Modern evolutionary theory the study of the bioevolutionary basis of behavior and development with a focus on survival of the genes Contributions and Criticisms of Ethological and Evolutionary Viewpoints Ethology shows us the value of studying human development in normal everyday settings and comparing human development with that of other species
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