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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 (0.0-1.0) 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