Download Heredity and the Environment

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