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Chapter

Ch 2. Genetic and Environmental Foundations.pdf

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Department
Psychology
Course Code
PSYC 2110
Professor
Vinod Goel

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2. Genetic and Environmental Foundations Wednesday, May 29, 20111:30 AM Genetic Foundations TheGeneticCode • Phenotypes-- observable characteristics • Genotype-- the complex blend of genetic information that determines our species and influences all our unique characteristics • Chromosomes-- rod-like structures that store and transmit genetic information ○ 23 matching pairs in humans; one is inherited from the mother and one from the father • Chromosomes are made up of DNA ○ Each rung of the DNA ladder consists of a pair of chemical substances called bases ○ This sequence of bases provides genetic instructions • A gene is a segment of DNA along the length of the chromosome ○ Genes can be of different lengths-- perhaps 100 to several thousand ladder rungs long • Individuals are about 99.1% genetically identical • A unique feature of DNA is that it can duplicate itself through a process calledmitosis ○ This allows the one-celled fertilized ovum to develop into a complex human being ○ Each new cell in the body contains the same number of chromosomes and the identical genetic information • Genes accomplish their task by sending instructions for making a rich assortment of proteins to thecytoplasm-- the area surrounding the cell nucleus TheSex Cells • Gametes-- sex cells (either sperm or ovum) ○ Contains only 23 chromosomes, only half as many as a regular body cell • Gametes are formed through a cell division process called meiosis, which halves the number of chromosomes normally present in body cells ○ First, the chromosomes pair up and each one copies itself ○ Then crossing over occurs, in which chromosomes next to each other break at one or more points along their length and exchange segments, so that genes from one are replaced by genes from another, creating new hereditary combinations Textbook Notes Page 1 ○ ○ The genetic variability produced by meiosis is adaptive-- it generates offspring that vary in phenotype, thus increasing the chances that at least some members of a species will survive ○ Meiosis results in 4 sperm cells, but only 1 ovum (the remaining genetic material degenerates) • When sperm and ovum unite at conception the resulting cell is called azygote Boyor Girl? • Autosomes-- the first 22 pairs of chromosomes (which are numbered from longest [1] to shortest [22]) • Sex chromosomes-- the 23rd pair of chromosomes (females-- XX, males-- XY) • Sex is determined by whether the sperm that fertilizes the egg carries an X chromosome or a Y chromosome MultipleBirths • Fraternal (dizygotic) twins are the most common type of multiple birth, resulting from the release and fertilization of two ova ○ Factors linked to fraternal twinning: ethnicity (highest among Asians), family history of twinning, age (peaks between 35 and 39 years), nutrition, number of births, and fertility drugs and in vitro fertilization • Identical (monozygotic) twins occur when a zygote that has started to duplicate separates into two clusters of cells that develop into two individuals Patterns of GeneticInheritance • Two forms of each gene occur at the same place on the chromosomes, one inherited from the mother and one from the father; each form of a gene is called an allele • Homozygous-- the alleles from both parents are alike • Heterozygous-- the alleles are different • Relationships between the alleles determine the phenotype • Dominant-Recessive Inheritance ○ In many heterozygous pairings, dominant-recessive inheritance occurs-- only one allele affects the child's characteristics (this is the dominant allele, the other is recessive and has no effect) Textbook Notes Page 2 dominant allele, the other is recessive and has no effect) ○ Heterozygous individuals with just one recessive allele can pass that trait onto their children; therefore, they are called carriers of the trait ○ Modifier genes enhance or dilute the effects of other genes • Incomplete Dominance ○ Incomplete dominance-- a pattern of inheritance in which both alleles are expressed in the phenotype, resulting in a combined trait, or one that is intermediate between the two ○ E.g., the sickle cell trait • X-Linked Inheritance ○ When a harmful allele is carried on the X chromosome, X-linked inheritance applies ○ Males are more likely to be affected because their sex chromosomes do not match ○ Many sex differences reveal the male to be at a disadvantage (e.g., rates of miscarriage, birth defects, learning disabilities, etc. are all higher for boys); however, 106 boys are born for every 100 girls to make up for this • Genomic Imprinting ○ In genomic imprinting, alleles are imprinted, or chemically marked, in such a way that one pair member (either the mother's or father's) is activated, regardless of its makeup  The imprint is often temporary ○ E.g., Prader-Willi syndrome, fragile X syndrome • Mutation ○ Mutation-- a sudden but permanent change in a segment of DNA ○ High-energy radiation over a long period impairs DNA ○ Germline mutation takes place in cells that give rise to gametes and is passed on to the next generation ○ Somatic mutation-- normal cells mutate, an event that can occur at any time of life  The DNA defect appears in every cell derived from the affected body cell, eventually becoming widespread enough to cause disease (such as cancer) or disability ○ Virtually all mutations are harmful, though not all (e.g., sickle cell anemia) • Polygenic Inheritance ○ Polygenic inheritance-- many genes affect the characteristic in question  E.g., height, weight, intelligence, and personality Chromosomal Abnormalities • Besides harmful recessive alleles, abnormalities of the chromosomes are a major cause of serious developmental problems • Most chromosomal defects result from mistakes during meiosis • Down Syndrome ○ Most common chromosomal disorder ○ Results from 3 chromosomes on the 21st pair (trisomy 21) ○ Symptoms include mental retardation, memory and speech problems, limited vocabulary, and slow motor development ○ Individuals benefit from intervention programs • Abnormalities of the Sex Chromosomes ○ Abnormalities of the sex chromosomes are often less severe than autosomal abnormalities (which often cause miscarriages) ○ Most common problems involve the presence of an extra chromosome (either X or Y) or the absence of one X in females  XYY syndrome  Triple X syndrome (XXX)  Klinefelter syndrome (XXY)  Turner syndrome (X0)-- missing X Reproductive Choices GeneticCounseling • Genetic counseling is a communication process designed to help couples assess their changes of giving birth to a baby with a hereditary disorder and choose the best course of action in view of risks and family goals • Pedigree-- a picture of the family tree in which affected relatives are identified Prenatal DiagnosisandFetal Medicine • Prenatal diagnostic methods-- medical procedures that permit detection of developmental problems before birth ○ E.g., amniocentesis, chorionic villus sampling, maternal blood analysis, fetoscopy, ultrasound, preimplantation genetic diagnosis • Frequently result in complications-- the most common being premature labor and miscarriage • Gene therapy-- correcting genetic abnormalities by delivering DNA carrying a functional gene to the cells • Proteomics-- scientists modify gene-specified proteins involved in disease Textbook Notes Page 3 TheAlternativeof Adoption • Most common among adults who are infertile, who are likely to pass along a genetic disorder, or who are older and single butwant a family • Adopted children tend to have more learning and emotional difficulties than other children, a difference that increases withthe child's age at time of adoption TheProsandCons of ReproductiveTechnologies • Donor Insemination and In Vitro Fertilization ○ Donor insemination-- injection of sperm from an anonymous man into a woman-- has been used to overcome male reproductive difficulties and has also been used by women without a male partner ○ In vitro fertilization-- a woman is given hormones that stimulate the ripening of several ova, which are then removed surgically and inseminated, then injected into the mother's uterus  Allows parents to select the sex of their child by injecting a single sperm into an ovum  About 50% of in vitro procedures result in multiple births, increasing the risk of low birth weight and major birth defects • Surrogate Motherhood ○ In vitro fertilization may be used to impregnate a woman (a surrogate) with a couple's fertilized ovum ○ Sperm from a man whose partner is infertile may be used to inseminate the surrogate who agrees to turn the baby over to the natural father ○ The surrogate is paid a fee • New Reproductive Frontiers ○ Postmenopausal women can become pregnant by using donor ova and IVF ○ Ethical concern over "designer babies" Environmental Contexts for Development TheFamily • In power and breadth of influence, no other microsystem context equals the family • Warm, gratifying family ties predict physical and psychological health throughout development • Contemporary researchers view the family as a network of interdependent relationships • Direct Influences ○ The behavior of one family members helps sustain a form of interaction in the other that either promotes or undermines children's well-being • Indirect Influences ○ Interaction between any two members is affected by others present in the setting (third parties) ○ Third parties can serve as supports or barriers to development ○ Coparenting-- parents mutually supporting each other's parenting behavior ○ Parental conflict can negatively impact a child's emotional health • Adapting to Change ○ The interplay of forces within the family is dynamic and ever-changing, as each member adapts to the development of other members ○ Parents' development affects children as well SocioeconomicStatusand FamilyFunctioning • Researchers assess a family's standing on this continuum through an index calledsocioeconomic status (SES), which combines three related variables: ○ Social status 1) Years of education 2) The prestige of one's job and the skill it requires ○ Economic status 3) Income • People in skilled and semiskilled manual occupations tend to marry and have children earlier as well as give birth to more children than people in professional and technical occupations • Commands, criticism, and physical punishment occur more often in low-SES households • Education contributes substantially to these variations in child rearing • As early as the second year of life, higher SES is associated with enhanced cognitive and language development and with reduced incidence of emotional and behavior problems • Higher-SES children do better in school Affluence Textbook Notes Page 4 Affluence • Affluent parents-- those in prestigious and high-paying occ
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