methodology in genetic research

what is genetic research in humans largely based on?

correlational studies; independent variable is not manipulated and there is no cause and effect

what methods were used prior to the human genome project?

1. twin studies (primary)

2. pedigree studies

3. prospective studies

4. adoption studies

monozygotic twins

come from one fertilized egg; identical genetics

dizygotic twins

come from two fertilized eggs; genetics similar to normal siblings

what are twin studies used for?

to see if there is possible correlation between genetic inheritance and behavior

what do psychologists base their hypotheses on how much genetic vs environmental factors influence behavior?

different degrees of genetic relationship. mz twins have higher degrees than dz.

the higher genetic relationship…

the higher chance that a trait they both have is genetic

"it should be the case that the higher the genetic relationship, the more similar individuals will be if the particular characteristic being investigated is inherited”

what is the correlation found in twin studies called? how is twin research analyzed?

concordance rates; analysis of similarity between mz and dz twins since any heritable trait will be more concordant in identical twins than in non-identical twins and even lower in siblings

how do we know that a trait is likely genetic with concordance rates?

the concordance rate for mz twins is a lot higher than dz twins or siblings

if concordance rate is high for both mz and dz twins…

environmental factors can be assumed to play a large role in the observed behavior instead of genetics

what are benefits and limits of twin studies?

Benefits

• not expensive

Limits

• hard to isolate environment as a control as twins usually grow up together in the same place

• may overestimate how similarly twins grew up (equal environment fallacy) as people treat identical twins more similarly than they do fraternal twins

• not highly representative of general population; hard to generalize

what is the concordance rate?

probability that the same trait will be present in both members of a pair of twins

what are the benefits and limits of family/pedigree studies?

Benefits

• more representative of the general population

how is pedigree studies conducted? what is the basis for them?

• child has 50% of genes from mom and dad; siblings share 50% of genes with each other; grandchildren share 25% of genes with grandparents; first cousins share 12.5% of genes with each other

• different degrees of genetic relatedness is compared to specific traits; a phenotype is traced over several generations to see if it is inherited

• if a trait is genetic, concordance rates will be higher in family members that share more genetics than, say, first cousins and strangers

explain Weissman et al (2005) may be asked explain one study of how kinship studies or twin studies may be used in the study of one behavior

• aim: studying the role of inheritance of behavior

• procedure: studies three generations over 20 years to determine level of inheritance of depression and anxiety

• results: showed that depression in grandparents was a greater predictor of depression in grandchildren than depression in parents

what are prospective studies and when are they used?

this when scientists suspect a behavior to be genetic within a family and decide to select a sample and observe them over time before certain behaviors are observed; they are looking for outcomes like the development of a disorder; these are used with genetically vulnerable populations but can be ethically wrong as they cause undue stress for the vulnerable

what are adoption studies and how do concordance rates work with it?

• allow direct comparison of genetic and enviornmental influences on behavior as adopted children share no genes with adoptive parents but 50% with each biological parent

• if a behavior is genetically high heritibility wise and enviornment plays little part, then the behavior should correlate more strongly with their bio parents and if the enviornment has the largest role, then it should correlate more with adoptive parents

what are the limits and strengths of adoptive studies?

Benefits

• most direct comparison of genetic and enviornmental influences on behavior

Limits

• children not representative of general population

• adoption agencies use selective placement to place kids with adoptive parents most similar to their biological ones; makes it harder to seperate genes from influences of enviornment

how did the human genome project change genetics research?

study heritibility via genetic mapping or linkage analysis. it shows which chromosome has a gene related to a behavior and where the gene is located on chromosome

how is linkage analysis done?

to create a genetic map, they collect blood from a family in which a behavior is common. they examine the DNA for polymorphism or genetic variation. these polymorphisms are genetic markers used in association studies

what do association studies do?

they see if there is a correlation/match between candidate genetic markers (polymorphisms) and a behavior. while more precise than twin studies, it is still correlational and needs a large research sample to see a signifianct effect, which is why GWAS is used

what does Genome Wide association studies do?

they compare the DNA of two groups where one group has the behavior and the other group is similar but doesn’t have behavior. this is because they suspect a gene is causing this. if a genetic marker (DNA) is more frequent in those with behavior, then it is “associated” with that disorder

“an examination of genome wide set of genetic variations in a large sample to see if any variations are associated with a trait”

what are the benefits and limits of GWAS?

Benefits

• large study preventing false conclusions influenced by outliers

what is used to make sense of GWAS?

a Manhattan Plot is used

• x-axis: chromsomes and the genes each one has

• y-axis: level of signifiance of association between genetic variation and behavior

• red line: required level of significance to see if a genetic variation is present between no behavior vs yes behavior (schizophrenia)

• peaks: show you what genes are different between the two groups and suggest that a combo of these genes may lead to this behavior; known as candidate genes

what are candidate genes?

researchers can’t say which gene causes what disorder but now have identified genes that require more research