Predicting Individual Differences Behavior Genetics

Behavior Genetics Chromosomes (book) Threadlike structures made of DNA molecules that contain the genes DNA (deoxyribonucleic acid) (chapters) Complex molecule containing the genetic information that makes up the chromosomes Genome (words) The complete instructions for making an organism, consisting of all the genetic material in that organism’s chromosomes The study of the relative power and limits of genetic and environmental influences on behavior

Identical vs Fraternal Twins Studies of identical twins versus fraternal twins, separated twins, and biological versus adoptive families allow researchers to tease apart the influences of heredity and environment. Separated identical twins: Maintain the same genes while testing effects of different home environments Adoptive families: Maintain the same home environment while studying effects of genetic differences

Heritability Heritability is the proportion of variation among individuals that can be attributed to genes. When you see a variation of some trait within a population, the heritability of that trait is the amount of variation in the population that is explained by genetic factors. Heritability does not reveal how much specific genes contribute to the trait for any one person.

Heritability Exercise Heritability is a direct correlation: It has a coefficient from 0 to 1. The more heritable a disease or trait is, the more the differences between people can be associated with genetic variation. Correlation does not imply causation (without the manipulation of variables). Most heritability estimates are based on correlational studies of monozygotic and dizygotic twins. Instead of saying that highly heritable diseases are “explained by genetics,” group differences are: associated with genetics variation linked with genetic variation tied to genetic variation

Heritability of a Disease List a highly heritable disease – a disease where group differences are connected to genetic variation.  Any diseases to right of x-axis – have estimate closer to 1 List a disease with low heritability – a disease where group differences are connected to environmental variation. Any diseases to left of x-axis – have estimate closer to 0 Heritability of a Disease

Examples

Generally speaking… Just because a disease or trait is associated with genetic variation, this does not account for the proportion of the trait or disease that is inherited. Heritability IS NOT the same as “inherited.” Look at the example of identical twins in #1: Identical twins have the same genetic make-up; however, differences between them are associated with environmental variation. Identical twins have low heritability. Heritability is a correlation or association. Associating a trait or disease with genetic variability does not mean it is CAUSED by genetics. For example, look at the 1950s example with earrings. In the 1950s, men in the U.S. did not wear earrings and women did. While most men and women grew up with the same cultural expectations, the differences between those who wore earrings and those who did not were associated with genetic variation (being female XX or being male XY). The environmental variability was low and the heritability was high. But being a woman did not CAUSE the growth of earrings! And women did not pass-down earrings from one generation to the next!

Molecular Behavior Genetics Molecular genetics is the study of the molecular structure and function of genes. Epigenetics is the study of environmental influences on gene expression that occur without a DNA change. Saying that genes are self-regulating means that genes are not blueprints; they can react differently in different environments. Its not genetic determinism. Nurture can change the way our genome is marked so it changes the phenome. It means we can do something about it! Nurture doesn’t change your DNA, but it can block the expression of the gene or activate it. Ted Talk: https://www.ted.com/talks/moshe_szyf_how_early_life_experie nce_is_written_into_dna#t-387345 (15 min)