bio approach: genetic similarity - twinship study

Question 1

gene definition:

Answer 1

a fundamental unit of heredity that carries the instructions for building, operating, and maintaining an organism.

Question 2

genetic similarity:

Answer 2

refers to the degree of shared genetic material between individuals or populations. it reflects the extent to which individuals inherit genetic variants, or alleles, from a common ancestor or gene pool.

Question 3

role of twin studies -

Answer 3

offering unique insights into the relative contributions of genetic and environmental factors. by examining pairs of twins who share varying degrees of genetic relatedness, researchers can disentangle the influence of genetics from environmental influences.

Question 4

study linked to this?

Answer 4

one such study, conducted by Kendler et al. (2006), delved into the heritability of major depressive disorder (MDD) using twins.

Question 5

kendler et al. 3 hypothesis q’s -

Answer 5

kendler and his team wanted to investigate three questions in their study:
- Past studies suggest a 35 - 45% heritability of major depression. Would this be true in a large Swedish sample?
- Are there significant gender differences in the heritability of major depression?
- Is there evidence that genetic and environmental factors in major depression differ over time?

Question 6

kendler et al. (2006) aim -

Answer 6

to determine the role that genetics plays in major depressive disorder.

Question 7

kendler et al. (2006) sample -

Answer 7

interview method - 15,493 complete twin pairs from the national Swedish Twin Registry.

only twins whose zygosity (whether they were identical or fraternal twins) could be verified were included in the study

Question 8

kendler et al. (2006) procedure -

Answer 8

trained interviewers conducted telephone interviews with the selected twins between March 1998 and January 2003. structured interviews -> gathered data on various aspects related to major depressive disorder (MDD) and potential contributing factors.

during the telephone interviews, the interviewers assessed lifetime major depression in the twins using modified criteria based on the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). the interviewers asked questions to determine whether the twins had experienced symptoms of major depression at any point in their lives.

the interviewers also asked questions about the twins’ shared environment, such as experiences during their upbringing when they were living in the same household.

also gathered information on individual-specific environmental factors, such as adult personal life events that may contribute to depression.

Question 9

kendler et al. (2006) after data collection: procedure -

Answer 9

the researchers analyzed the information obtained from the interviews -

they calculated concordance rates for major depression among twin pairs, examining whether both twins in a pair were affected by major depression.

they also calculated correlations between major depression and zygosity (identical vs. fraternal twins), which provided insights into the genetic and environmental influences on major depression.

Question 10

kendler et al. (2006) results -

Answer 10

concordance rates for lifetime major depression:
Female-Female, MZ - 0.44
Female-Female, DZ - 0.16
Male-Male, MZ - 0.31
Male-Male, DZ - 0.11
Male-Female, DZ - 0.11

concordance rates for major depression were significantly higher in women than in men.

the correlations were significantly higher in monozygotic twins compared to dizygotic twins, suggesting a genetic influence on major depression.

the estimated heritability of major depression was 0.38, consistent with previous research.

there were no significant differences observed in the roles of genetic and environmental factors in major depression across different birth cohorts or before and after World War II.

Question 11

conclusion -

Answer 11

highlights the significance of twin research in elucidating the genetic basis of psychiatric disorders.

by analyzing large cohorts of twins, the study provided compelling evidence for the heritability of depression and identified potential gender differences in genetic susceptibility.

underscore the enduring relevance of twin studies in advancing our understanding of genetics and informing targeted interventions for complex traits and disorders.