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.In other words, after theindividual grew up and left his family of origin, early environmental influencesmattered less and less.This way of studying genetics isn t perfect.You can assumemonozygotic twins have the same genetic makeup and dizygotic twins do not.However, a complicating concern is whether monozygotic twins have the sameexperiences or environment as dizygotic twins.Some identical twins are dressed alikeand are even given similar names.Yet the twins influence each other s behavior, andin some cases, monozygotic twins may affect each other more than dizygotic twins(Carey, 1992).Durand 3-99One way to address this problem is by combining the adoption study and twinstudy methods.If you can find identical twins, one of whom was adopted as an infant,you can estimate the relative roles of genes and the environment (nature versusnurture) in the development of behavioral patterns.Genetic Linkage and Association StudiesThe results of a series of family, twin, and adoption studies may suggest that aparticular disorder has a genetic component, but they can t provide the location of theimplicated gene or genes.To locate a defective gene, there are two general strategies:genetic linkage and association studies (Merikangas & Risch, 2003).The basic principle of genetic linkage studies is simple.When a family disorder isstudied, other inherited characteristics are assessed at the same time.These othercharacteristics called genetic markers are selected because we know their exactlocation.If a match or link is discovered between the inheritance of the disorder andthe inheritance of a genetic marker, the genes for the disorder and the genetic markerare probably close together on the same chromosome.For example, bipolar disorder(manic depression) was studied in a large Amish family (Egeland et al., 1987).Researchers found that two markers on chromosome 11, genes for insulin and aknown cancer gene, were linked to the presence of mood disorder in this family,suggesting that a gene for bipolar disorder might be on chromosome 11.Unfortunately, although this is a genetic linkage study, it also illustrates the danger ofdrawing premature conclusions from research.This linkage study and a second studythat purported to find a linkage between the bipolar disorder and the X chromosome(Biron et al., 1987) have yet to be replicated; that is, different researchers have notbeen able to show similar linkages in other families (Craddock & Jones, 2001).The inability to replicate findings in these studies is common (Altmuller, Palmer,Durand 3-100Fischer, Scherb, & Wjst, 2001).This type of failure casts doubt on conclusions thatonly one gene is responsible for such complex disorders.Be mindful of suchlimitations the next time you read in a newspaper or hear on TV that a gene has beenidentified as causing some disorder.The second strategy for locating specific genes, association studies, also usesgenetic markers.Whereas linkage studies compare markers in a large group of peoplewith a particular disorder, association studies compare such people and peoplewithout the disorder.If certain markers occur significantly more often in the peoplewith the disorder, it is assumed the markers are close to the genes involved with thedisorder.Association studies are thus better able to identify genes that may onlyweakly be associated with a disorder.Both strategies for locating specific genes shednew light on the origins of specific disorders and may inspire new approaches totreatment (Merikangas & Risch, 2003).Studying Behavior over TimeSometimes we want to ask,  How will a disorder or behavior pattern change (orremain the same) over time? This question is important for several reasons.First, theanswer helps us decide whether to treat a particular person.For example, should webegin an expensive and time-consuming program for a young adult who is depressedover the loss of a grandparent? You might not if you knew that with normal socialsupports the depression is likely to diminish over the next few months withouttreatment.On the other hand, if you have reason to believe a problem isn t likely to goaway on its own, you might decide to begin treatment.For example, as we see later,aggression among very young children does not usually go away naturally and shouldbe dealt with as early as possible.It is also important to understand the developmental changes in abnormal behaviorDurand 3-101because sometimes these can provide insight into how problems are created andbecome more serious.For example, we will see that some researchers identify peoplewho are at risk for schizophrenia by their family histories and follow them through theentire risk period (18 45 years of age) (see Tsuang, Stone, & Faraone, 2002).Thegoal is to discover the factors (e.g., social status and family psychopathology) thatpredict who will manifest the disorder.(This complex and fascinating research isdescribed in Chapter 12.)Prevention ResearchAn additional reason for studying clinical problems over time is that we may be ableto design interventions and services to prevent these problems.Clearly, preventingmental health difficulties would save countless families significant emotional distress,and the financial savings could be substantial.Prevention research includes the studyof biological, psychological, and environmental risk factors for developing laterproblems (called preintervention research); treatment interventions to help preventlater problems (called prevention intervention research); and more widespreadstructural issues such as governmental policies that could assist with preventionefforts (called preventive service systems research) (NAMHC Workgroup on MentalDisorders Prevention Research, 1998).The research strategies used in preventionresearch for examining psychopathology across time combine individual and groupresearch methods, including both correlational and experimental designs.We looknext at two of the most frequently used: cross-sectional and longitudinal designs.Cross-Sectional DesignsA variation of correlation research is to compare different people at different ages.Fora cross-sectional design, researchers take a cross section of a population across theDurand 3-102different age groups and compare them on some characteristic.For example, if theywere trying to understand the development of alcohol abuse and dependence, theycould take groups of adolescents at 12, 15, and 17 years of age and assess their beliefsabout alcohol use.In such a comparison, J.Brown and P.Finn (1982) made someinteresting discoveries.They found that 36% of the 12-year-olds thought the primarypurpose of drinking was to get drunk.This percentage increased to 64% with 15-year-olds but dropped again to 42% for the 17-year-old students.The researchers alsofound that 28% of the 12-year-olds reported drinking with their friends at leastsometimes, a rate that increased to 80% for the 15-year-olds and to 88% for the 17-year-olds.Brown and Finn used this information to develop the hypothesis that thereason for excessive drinking among teens is a deliberate attempt to get drunk ratherthan a mistake in judgment once they are under the influence of alcohol.In otherwords, teenagers do not, as a group, appear to drink too much because once they vehad a drink or two they show poor judgment and drink excessively [ Pobierz całość w formacie PDF ]