Heredity and the Environment Chapter 2

Biological characteristics interact with the human environment to yield the individual psychological characteristics that emerge from species and individual attributes: 1.Species—Environment Fit: Evolutionary Processes 1.Individual—Environment Fit: Biopsychosocial Processes

Genotype: Genetic code for the individual Phenotype: Manifestation of the genotype Both can be impacted by the environment –Toxins –Disease –Mutations –Etc…

Gene—Segment of DNA that synthesizes a particular protein; contains the key to any inherited characteristic Chromosome—Carrier of genes in a particular patter; 23 pairs; –22 pairs are linked to non-sex specific attributes –1 pair linked to sex-specific attributes Female—2 X chromosomes Male—1 X and 1 Y chromosome

Diversity and Reproduction –Zygote: following initial cell division of the fertilized egg Mitosis—Exact replication of 22 non-sex linked chromosomes (autosomes) Meiosis—When sex cells (egg & sperm) replicate, genetic material is shuffled and each chromosome has 23 single stranded chromosomes; when sperm and egg unite, there is a unique pairing of chromosomes, thus genetic diversity is accomplished

Exception to the rule: Monozygotic Twins –Initial zygote divides with two identical replications –All genetic material is the same –Monozygotic twins have been objects of much research on heritability of human characteristics Dizygotic Twins –Same process as siblings except for simultaneous pregnancy

Dominant & Recessive Genes Dominant genes—expressed in the presence of another Dominant or a Recessive gene Recessive genes—only expressed in the presence of another recessive gene Dominant-Recessive patterns determine the likelihood of a given characteristic being expressed

Inherited Anomalies Dominant Gene Anomalies –Huntington Disease (progressive neurological damage –Progeria Disease (premature aging) Recessive Gene Anomalies –Cycle cell anemia (defective hemoglobin) –Cystic fibrosis (affects lungs, gastrointestinal tracks)

Inherited Anomalies Sex-Linked (genetic anomalies) –Congenital deafness –Hemophilia Chromosomal anomalies –Down’s Syndrome (trisomy 2) –Likelihood associated with maternal age (note this is correlational)

Inherited Anomalies Pre-conception genetic testing Couples contemplating conception are screened for likelihood of passing on anomalous traits Prenatal Screening –Ultrasound—can be unreliable –Amniocentesis—potential damage to fetus –Chorionic villus sampling—risk of inducing miscarriage Ethics, values, and who decides

Genetic—Environment Interaction Range of Reactions: Genes place limits on range of reactions of phenotypic responses Canalization: genotype provides a series of likely pathways and the environment nudges the individual into one or more

Genetic—Environment Interaction Niche-Picking: individuals are more or less suited for particular environmental niches; –Passive: infant’s environment typically determined by those who contributed genetic make-up –Evocative: child’s phenotypic expressions of genotype evoke particular responses from caregivers and others –Active/Niche-Picking: offspring actively select environments that fit the phenotypic expression of genotype (Scarr, 1992)

Genetic—Environment Interaction Probabilistic Epigenesis –As organism develops, environmental stimuli are necessary to turn on genes –Presence and magnitude of stimulation impact the nature of the genetic expression –Similar to ethological concept of sign stimulus and action potential (see Gotlieb, 1997)

Behavioral Genetics Heritability of traits –Estimation ( ) of genetic influence –Related to Prevalence of trait in biological parentage Shared and non-shared environment –Based on comparison of monozygotic and dizygotic twin studies with shared and non-shared environments –Estimates average about.5 across traits (Table 2.4, pg 73 & 74) –Niche-Picking and Probabilistic Epigenesis likely explanations

What we know: Nature and nurture play a role Genotypes are expressed as phenotypes Environmental and cultural factors impact the effect of phenotypic differences Genetics and shared/non-shared environments are likely responsible for significant variance in individuals