Heredity and the Environment

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Heredity and the Environment

• Chapter 2

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• Biological characteristics interact with the
  human environment to yield the individual
  psychological characteristics that emerge from
  species and individual attributes
• SpeciesEnvironment Fit Evolutionary Processes
• IndividualEnvironment Fit Biopsychosocial
  Processes

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

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• GeneSegment of DNA that synthesizes a particular
  protein contains the key to any inherited
  characteristic
• ChromosomeCarrier of genes in a particular
  patter 23 pairs
• 22 pairs are linked to non-sex specific
  attributes
• 1 pair linked to sex-specific attributes
• Female2 X chromosomes
• Male1 X and 1 Y chromosome

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• Diversity and Reproduction
• Zygote following initial cell division of the
  fertilized egg
• MitosisExact replication of 22 non-sex linked
  chromosomes (autosomes)
• MeiosisWhen 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

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• 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

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Dominant Recessive Genes

• Dominant genesexpressed in the presence of
  another Dominant or a Recessive gene
• Recessive genesonly expressed in the presence of
  another recessive gene
• Dominant-Recessive patterns determine the
  likelihood of a given characteristic being
  expressed

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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)

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Inherited Anomalies

• Sex-Linked (genetic anomalies)
• Congenital deafness
• Hemophilia
• Chromosomal anomalies
• Downs Syndrome (trisomy 2)
• Likelihood associated with maternal age (note
  this is correlational)

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Inherited Anomalies

• Pre-conception genetic testing
• Couples contemplating conception are screened for
  likelihood of passing on anomalous traits
• Prenatal Screening
• Ultrasoundcan be unreliable
• Amniocentesispotential damage to fetus
• Chorionic villus samplingrisk of inducing
  miscarriage
• Ethics, values, and who decides

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GeneticEnvironment 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

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GeneticEnvironment Interaction

• Niche-Picking individuals are more or less
  suited for particular environmental niches
• Passive infants environment typically
  determined by those who contributed genetic
  make-up
• Evocative childs 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)

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GeneticEnvironment 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)

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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

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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