BEHAVIOR GENTEIC FINDINGS Genetics 50 Nonshared environment 40 Shared environment 10 there is nothing anti sociological about BG methods in fact BG methods are the most reliable way to estimate environmental effects allows us to directly and accurately estimate environmental influences on a given phenotype differentiates between shared and nonshared environmental influences how do we estimate these effects most researchers including criminologists look at only one child per family can t separate genetic from environmental influences need to look at more than one child per family Twin based design is the most common technique Natural Experiment Why we can compare monozygotic twins MZ to dizygotic twins DZ MZ twins identical twins DZ twins fraternal twins TWIN STUDIES based a fairly assumption what else could account for this finding why not the shared environment influence MZ twins share the same environment DZ twins share the same environment genetic material CRITICISMS OF TWIN STUDIES if MZ twins are more similar to each other than DZ twins then genes have great influence If DZ twins are just as similar to one another as MZ twins then the environment has a greater The only reason that MZ twins would be more similar to another would be because the share twice as much critics of twin based research have argued that there are serious limitations of the twin based design argue that these limitations result in artificially inflated h2 estimates also result in artificially deflated C2 and E2 estimates 1 Violationof the equal environments assumption EEA MZ twins share environment that are more similar than DZ twins since they are genetically identical 2 Presence of assortative mating mates seek out other mates with genomes that are similar to their own results in DZ twins that may share more than 50 of their dissenting DNA Responses to criticisms Violation of the EEA studies have examined misclassified MZ DZ twin pairs e g classified as a Dz pair but is actually an Mz pair Mz Mz Dz Mz Mz Dz Dz Dz No support for inflated estimates of h2 assortative mating studies have found support for assortative mating increases the genetics similarity between non M2 siblings works to decrease estimates of h2 not increase them only artificially deflated 2 18 14 Other BG Techniques limitations not a concern 1 Adoption studies 2 Mz twins separated at birth MzA 3 Family Studies Adoption Studies additional techniques have been developed anyways researchers have developed additional methods to separate genetic environment influences we can estimate h2 c2 and e2 with adoption studies we don t just need to twins we can compare the adoptees with their biological parents and with their adopted parents If the adoptee more closely resembles their biological parents then genes influences the examined phenotype If the adoptee more closely resembles the adopted parents then the environment has a stranger influence on the examined phenotype M2 Twins separated at birth we can also examine Mz twins who were separated at birth MzA these are rare samples but some studies have identified an impressive number of MzA twins any resemblance between them would be due to genetics no share environment remember that nonshare environments make siblings different from one another ex shows such as sister sister parent trap Family Studies logic of MZ twin based design can be extended to other family members as well most common use is with non twin sibling pairs full sibling half sibling cousin etc also possible with biological parents Share genes 1 parents 50 Full siblings 50 Half siblings 25 Cousins 12 use parents score on the phenotype of interest as a gross genetic measure possible anytime we compared at least 2 people from the same household Sibling Type Mz Dz Full sibling Half sibling cousins Level genetic relation 1 00 50 50 25 125 A C genetic risk 5 4 4 3 2 need to know the level of genetic relatedness FINDING FROM BG what do BG studies reveal about the heritability of behavior and personality traits findings are relatively consistent across different methodologies indicates that the results from any one method are valid and reliable most behaviors personality traits are highly heritable 50 90 50 represents a proportion can be converted 2 a percentage 50 The shared environment has very little effect The non shared environment is important Findings are so robust they have been developed into formally written laws 3 Laws of Behavior 1 First law All human behavioral traits are heritable 2 Second law The effect of being raised in the same family is smaller than the effect of genes 3 Third law A substantial portion of the variation in complex human behavior traits is not accounted for by the effects of genes or families Behavior Genetics BG methods provide us with a good starting point Don t provide much detail what genes are influencing the phenotype what environments are influencing the phenotype 2 20 14 Genes Introduction to Genetics genes that are responsible for the development of problem behaviors and traits There are approximately 25 000 genes in the human body Genes are stretches of DNA that work together to perform specialized functions To better understand genes we need to discuss DNA DNA is a chemical code that allows us to form develop and function DNA is stored in the nucleus of every cell except red blood cells information encoded into DNA determines virtually every observable and many unobservable characteristics one of the reasons that people are different is because their DNA varies every person has their own unique sequence of DNA except M2 each person s arrangement of genes is referred to as a genotype The structure of DNA 2 fibers twisted around each other to form a double helix each fiber is referred to as a polynucleotide along the backbone of each polynucleotide is a sequence of nucleotides also called bases There are four different types of bases 1 Ademine A 2 Thymine T 3 Cytosine C 4 Guanine G The four bases nucleotides make up the genetic alphabet How are the two polynucleotides held together through bonds between the bases A only pairs with T G only pairs with C These bonds hold the two strands of DNA together The ordering of base pairs is very important Small changes can have large effects on physical and mental health physical appearance even behavior just an estimate humans and chimpanzees share over 96 of their DNA humans share approximately 99 9 of their DNA responsible for all of the similarities