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PSY 1102 Lecture Notes - Personal Development

Course Code
PSY 1102
Christine Mountney

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Class 2: Nature, Nurture, and Human Diversity
Behavior Genetics: Predicting Individual Differences
Genes: Our Codes for Life
Twin and Adoption Studies
Temperament and Heredity
Gene-Environment Interaction
The New Frontier: Molecular Genetics
Behavior Geneticists study our differences and weigh the relative effects of heredity and
Genes: Our Codes for Life
Chromosomes containing DNA (deoxyribonucleic acid) are situated in the nucleus of a
Segments within DNA consist of genes that make proteins to determine our development.
Genome is the set of complete instructions for making an organism, containing all the
genes in that organism. Thus, the human genome makes us human, and the genome for
drosophila makes it a common house fly.
Genotypes: traits that result due to inheritance alone
Phenotypes: traits that result from a combination of genes and environmental influences
Alleles: variations within a gene can arise from a mutation
Allelic Variants
Huntingdon’s Disease: Dominant just need one copy of gene 50% chance of
developing if one parent has it (variant on Huntingtin gene)
Cystic Fibrosis: - Recessive mutation on CFTR gene both copies of gene need to be
defective to get CF
HLA Gene: people with HLA-B*1502 or HLA-A*3101 are more susceptible to
developing serious skin disorders (ie., SJS or TEN) with anti-epileptic use (ie.,
Women with BRCA1 or BRCA2 genetic alleles have higher risk of developing breast
Twin and Adoption Studies
Studying the effects of heredity and environment on two sets of twins, identical and fraternal, has
come in handy.
Identical: same genetic material and the egg splits in half, so the one set of DNA is split between
the two and they often share the same placenta
Fraternal: two different sperm fertilize two different eggs at the same time, with two different
sacs and two different placentas

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Identical vs. Fraternal Twin Similarities and Differences
Genetic influences
Identical twins share a much higher risk of developing similar disease than fraternal
Identical twins more similar on scores of extraversion and neuroticism
Social Influences
Identical twin divorce rate much higher if one divorces compared to fraternal twins
Identical twins treated more alike by parents than fraternal twins
Identical twins are often treated the same in a social environment in comparison to
fraternal twins.
Separated Twins
A number of studies compared identical twins reared separately from birth, or close
thereafter, and found numerous similarities.
Critics of separated twin studies note that such similarities can be found between
strangers. Researchers point out that differences between fraternal twins are greater than
identical twins.
Similar gestures, tones, movements and present themselves in very similar ways even
when raised apart in comparison to fraternal. More alike than siblings and or fraternal
twin raised together
Biological Versus Adoptive Relatives
Adoption studies, as opposed to twin studies, suggest that adoptees (who may be
biologically unrelated) tend to be different from their adoptive parents and siblings.
Whether an adopted child more so resembles their adoptive brothers, sisters and parents,
or if you reintroduced them to their biological family would they be more similar.
They are more similar to their biological family rather than their adoptive family.
Adoptive Studies
Adoptive studies strongly point to the simple fact that biologically related children turn
out to be different in a family. So investigators ask:
o Do siblings have differing experiences?
o Do siblings, despite sharing half of their genes, have different combinations of
the other half of their genes
o Does parenting have an effect?
Siblings do have different experiences. Many children within one family are raised
differently by their parents because of their temperament etc.
There is a lot of variability that happens within the genes that make siblings different
from each other
Parenting does have an effect on biologically related and unrelated children.
Parenting Influences Children’s: attitudes, values, manners, beliefs, faith, politics
Temperament and Heredity
Temperament refers to a person’s stable emotional reactivity and intensity. Identical
twins express similar temperaments, suggesting heredity predisposes temperament.
The extent to which differences among people are attributable to genes
Heritability is influenced by environment:
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