IIC.  Behavioral Genetics
	1.  Chromosomes, Genes, & Cistrons
			a.  Basic definitions and concepts
	2.  Monogenic Traits
			a. Human phenylketonuria: many effects 						of single gene
			b.  Hygienic honeybees: monogenic fine-						tuning of behavior
	3. Polygenic traits and heritability (h2)
			a. Detecting polygenic contribution to 							"gradual"  traits
			b.  Heritability and IQ
			c.  Fragility of heritability: 								gene/environment interaction  
	4. Gene - Brain - Behavior: Paths of Causation
			a.  Genetic coding of brain structure
			b.  Direct gene-to-neuron coding versus 							indirect "development rules"
			c.  Interaction with developmental 							environment						
	
Reading
  Coursepack: Behavioral Genetics by Alcock 
(For background read Kalat appendix A and re-read Dawkins 3) 
For gene-to-brain causation, read Kalat pp. 299-305

For next topic begin  Kalat Chapter 2

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CHROMOSOMES & GENES
Although Humans have 46 Chromosomes, in 23 pairs, other species have more or less (Chimp 48 in 24 pairs)

Important point is that genes contained on chromosomes act as matched pairs:  Vol 1a,1b    2a,2b   (or editions using Dawkins analogy of encyclopedia)

Volumes may be the same  in which case the gene is HOMOZYGOUS	
Or volumes may be different.  Then genes are HETEROZYGOUS, and the two different forms are  ALLELES 
	Dominant or  Recessive

-Chromosomes are STRANDS of DNA Molecules linked 
-DNA molecules are smaller chains of   4 TYPES of NUCLEOTIDES
-The types of nucleotides in a chain determines the type of protein cell will make.
-Particular chain of nucleotides that codes 1 protein is a CISTRON (in Dawkin's terms)

Humans have 100,000 cistrons
Thus the influence of genes on human physiology and behavior is limited largely to what they can accomplish by coding variations in the production and expression of 100,000 proteins.  This poses a bottleneck for genetic influences, and is one reason why most human traits of interest are polygenic.

TYPES OF TRAITS:
1. MONOGENIC TRAITS
Occasionally a single cistron is so important & unique that presence of cistron = trait 
  [eye color, sensory taste, color vision]

There are a few examples in human behavior of monogenic traits
Most famous may be PHENYLKETONURIA  (PKU)    
1 baby in 15,000   (screened by blood phenylalanine)
PKU infant:	normal at birth
		Slowed development, physical and mental
		Sensorimotor changes:  rigid movements & gait
		Emotional changes:  Agitation, crying, distress
		Cognitive changes:  IQ under 70  (lowest 2 percentile)
-Due to a single recessive gene (not sex chromosome): 1 person in one hundred carries allele    (homozygous = PKU;  heterozygous=normal)
-Lacks liver enzyme: Phenylalanine hydroxylase   
(food phenylalanine   via Ph. hydroxylase => tyrosine...eventually Dopamine)
-If no hydroxylase,  conversion instead to PHENYLPYRUVIC ACID
-Therapy:  Diet for first 5 - 10 years

Other species have more focused monogenic traits that allow behavioral fine-tuning
Example:  HYGIENIC HONEYBEES
Two monogenic traits for removal of diseased larvae
)
Recent claims for  human specific behavioral traits linked to single genes (from molecular genetics studies):
Some straightforward: Huntington's disease on Chromosome 4
	Some forms of Intersexuality 		
Others claims are highly controversial :
		Schizophrenia link to chromosome 5 (debated; only small proportion of schizophrenics)
		Alcoholism link to site near dopamine receptor gene
		Homosexuality link to X chromosome

POLYGENIC TRAITS
-Depend upon whole COMPLEXES of genes, interacting with environment
-These change by slow degrees (selection analogous to DAWKIN'S Rowers]:

Effect of "poly-cistron genes" must be studied by POPULATION effects
	 Mean and Variance (V)
	  Vphenotype= Vgenotype + Venvironment   + 2 CO V

HERITABILITY = h2 = VG / (VG + VE)    (ratio between 0 and 1)
= relative role of genetic variation in producing pheno variation (in given Environment)

Regarding predictions for IQ scores and other traits, h is not a constant. 
	Its strength & predictive value DEPENDS entirely upon the population and environment range in which it was	measured.  Even PKU, which is extremely simple, could in principle be made to vary in h.

HOW do genes affect IQ or other behavioral traits?
This is a question of MECHANISM.  We have to ask how genes influence brain development.
The bottleneck of limited number of cistrons rules out the possibility of having a single gene for each trait, or even a single gene for each neuron. (since there are 100 BILLION human neurons = 100,000,000,000   =   1011 neurons)

But genes can code development factors that affect pattern of brain growth, even if they can't code the brain's 'blueprint'.
Factors include:
-Presence of particular proteins (that influence cell type,  neurotransmitter production)
-Timing of development

 Gene factors are expressed in EPIGENESIS (gene/env interaction) of brain development.
	A.   example: CAMs - Cell Adhesion Molecules: modulate direction, timing of neuron growth  
	B. Cell death: influenced by competition among developing neurons
These factors interact both with  other genes and with environmental events
	(A chief reason why drugs affect fetal brain development)