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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: Species—Environment Fit: Evolutionary Processes
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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: • Species—Environment Fit: Evolutionary Processes • 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