Behavioral Genetics

Temperament – that portion of a person’s personality that has an organic, and therefore genetic, basis. It is has been acknowledged for centuries that some portion of the personality has an organic basis, e.g. personality differences between men and women. It is obvious that some of these differences can be attributed to specific proteins, e.g. the hormones testosterone and estrogen.

Chronic and Bipolar Depression Genealogy of a family from the Central Valley of Costa Rica. Deceased persons are marked with a slash.

It has been difficult to identify the specific genes behind bipolar depression because it is a polygenic trait, a trait caused by the joint action of multiple genes.

The midbrain (mesencephalon): center for emotions and sex hypothalamus

Synapses, neurotransmitters, and receptors

Novelty- or Thrill-Seeking, and Addiction Dopamine synthesis

People who psychologists would describe as thrill, or novelty seekers have been shown to have a mutation of the D4DR receptor allele, found on chromosome 11. All addictions involve affecting the release, reuptake, or regulation of dopamine. Reuptake: the transporting of a neurotransmitter back inside a dendrite by means of transporter protein.

Dopamine and addiction

Serotonin and Depression Serotonin – Synthesized from the amino acid tryptophan. Is involved in both relaxation and aggression. Selective Serotonin Reuptake Inhibitors: Zoloft, Prozac.

There is controversy about the role played by the serotonin transporter in chronic depression – whether it is too efficient at transporting serotonin (the majority opinion) or defective in transporting serotonin (Dean Hamer), in which case Prozac and Zoloft should be seen a synthetic serotonin transporter proteins.

Minnesota Twins Project Initiated by Thomas J. Bouchard in 1981 Studied Monozygotic Twins that were adopted separately as infants. The correlation coefficient R represents the degree of similarity between twins, and hence the extent of the genetic component to the variable.

Intelligence and IQ

Six conclusions concerning tests of cognitive ability (Herrnstein and Murray:22): 1.There is such a thing as a general factor of cognitive ability on which human beings differ. 2.All standardized tests of academic aptitude or achievement measure this general factor to some degree, but IQ tests expressly designed for this purpose measure it most accurately.

3. IQ scores match, to a first degree, whatever it is that people mean when they use the word intelligent or smart in ordinary language. 4. IQ scores are stable over much of a person’s life. 5. Properly administered IQ tests are not demonstrably biased against social, economic, ethnic, or racial groups. 6. Cognitive ability is substantially heritable, apparently no less than 40% no more than 80%.