The Genetics of Behaviour


I.  Behavioral Traits:

        How a person communicates,
        Copes with rage,
        Handles stress,

  Disorders with behavioral symptoms:

        Mood alteration...

Most behavioral disorders affect more than 1 in 1,000 individuals and are caused by several genes and the environment----  They are common, polygenetic and multifactorial.

II.  Tools to study behaviour genetics:

        Empiric risk estimates
        Adoptee and twin studies;

New approaches:  1.  Association studies that correlate genetic markers such as SNP (single
                                 nucleotide polymorphism) patterns with particular symptoms.

                            2.  Analysis of mutations in specific candidate genes that are present
                                 exclusively in individuals with the bahaviour. 

III.  Behavioral genetics:  A study of nervous system variation and function.  Genes control the synthesis, levels, and distribution of neurotransmitters, which are the chemical messengers that connect nerve cells (neurons) into pathways.  Signal transduction is also a key part of the function of the nervous system.


IV.  Examples of behavioral genetic traits:

        ADHD  (attention deficit hyperactivity disorder) has a heritability of  H = 0.8.  Linked to the
                     function of a neurotansmitter  --- dopamine.

        Autism:  Individual does not speak or interact with others and is comfortable only with
                      restricted or repetitive behaviours.  Heritability of 0.6 ~ 0.9.

        Eating disorders:  Anorexia nervosa.  H = 0.5 ~ 0.8
                                     high risk genes include those traits that control the traits of perfectionism,
                                     orderliness, low tolerance for new situation, maturity fears, low
                                     self-estemm, and overall anxiety.

        Sleep:  disorder called: "narcolepsy with cataplexy"

                    Narcolepsy:  Produces daytime sleepiness and the tendency to fall asleep very rapidly, serveral times a day. 

                    Cataplexy:     A short episodes of muscle weakness, during which the jaw sags, head drops, knees buckle, and the     
                                         person falls to ground.

                    H = 0.25 ~ 0.31

                    Familial advanced sleep phase syndrome (FASPS):
      Intelligence:  the ability to reason, learn, remember, connect ideas, deduce and create.
            H = 0.8
        In 1904, Alfred Binet developed a test with verbal, numerical, and pictorial questions, and
        then modified at Stanford University.  Called "Intelligence Quotient" - IQ

        An average score on IQ test is 100, two-thirds of all people scoring between 85 and 115.
        figure 8.4.


Drug Addiction: 
The compulsive behavior of seeking and taking a drug despite knowing its
                                    adverse effects.

        Two identifying characteristics:

            1.  Tolerance:  the need to take more of the drug to achieve the same effects as time goes
               2.  Dependence:  the onset of withdrawal symptoms when a person ceases taking the drug.

        Drug addiction produces stable, rather than temporary, brain damages.
            H = 0.4 ~ 0.6
            Human equivalents of the opiates are the endorphins and enkephalins, which are
            equivalent to plant-derived chemicals, cocaine, opium, and tetrahydrocannabinol (THC).
            Alcohol dehydrogenase, and an allele of the gene that encodes the dopamine D(2)
            receptor.  High percentage people with alcoholism are homozygous for the A1 allele of
            D(2) dopamine receptor gene.

Mood Disorders:

        Major depressive disorder: H = 0.4 ~ 0.6

        Bipolar affective disorder:  H = 0.8

            Serotonin  --- neurotransmitter


        A debilitating loss of the ability to organize thoughts and perceptions, which leads to a
        withdrawal from reality.
        H = 0.8