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Summary Twin research in psychology lectures (1 t/m 13)
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Summary of the book 'Behavioral Genetics (7th Edition). Editors Knopik, Neiderhiser, DeFries, and Plomin. New York, NY: Worth'
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Summary Behavioral Genetics by Knopik (Minor Brain & Mind)
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Twin Research in psychologyLecture 1 (1A)
Finish more than 80% of the assignment before the exam
- every lecture has one assignment to keep you active
- Block assignment is an obligation: submit and give feedback (2 peers)
- 16 December last lecture on zoom
Historical perspective
- where do all differences came from?
Parents pass traits on to offspring
- Pythagoras
- Aristotle though children were made of blood testes + menstruation blood because
menstruation stops by pregnancy
Nicolaas + Anatonie microbiology
- theory of preformationism = we all come from miniature versions of ourselves human have
sperm with an individual
- benefits with this theory: Adam to all humans, original sin (zonde)
Francis Galton psychometrics, behavior genetics
- family trees
- twins
- understand genetic influences
Charles Darwin most important trip in all of science
- voyage
- father: waste of time
- Bird Galapagos: designed for the food what there was on the island
- Theory of evolution: all species arose through the natural selection of small, inherited variations
that increase the individuals’ ability to survive and reproduce
- also, emotions
- Every part of the body egg embryo
- Blending inherited: blending/mix of traits
Problem of this blending theories of inheritance for theory of evolution
- small inheritance selected
- er komt na een tijdje geen middelgetal meer uit, omdat iedereen al average is, iedereen zal dan
uiteindelijk gemiddeld zijn/even groot zijn (dat is niet zo)
Mendel
- pedigree (= stamboom) of hemophilia (bloedziekte) in the royal families of Europe
- crossing to find any pattern (inheritance) with seeds, plants, flowers (smooth one, wrinkle one
all smooth = glad) all smooth because one was dominant
- cross again all smooth woman and all smooth man: children ¾ smooth and ¼ wrinkled
- How could that be? Trait of two generations before, come back now
- after mixing more colors color is gone: all black = blending inheritance
- met draad door elkaar, je kan de kleur nog terugkrijgen = the case by the traits that coming back
two elements of heredity for each trait in each individual Mendel’s first insight = Mendel’s first
law: Two elements give one of them child get one of father and mother
,Punnet square diagram to cross the genotypes useful to determine the probability of an
offspring having a particular genotype
- Dominant Allele = expresses its phenotypic by hetero
- Recessive Allele = expresses not its phenotypic by hetero
Now it makes sense the problem of blending inheritance = not true
What happened when Mendel looked at two or more traits at the same time?
- realized: one trait does not influence the other. Inheritance will be random (random change) = law
of independent assortment = Mendel’s second’s law
Gene = basic unit of inheritance
Allele = alternative variants of gene
Genotype = combination of alleles at a region/gene
Phenotype = observed trait of an organism (blue eye)
Homozygosity = 2 same alleles
Heterozygosity = 2 different alleles
Chromosome = physical units of inheritance
Genome = all DNA sequences of an organism
Mendelian disorders
- Huntington’s disease = brain disorder one gene = dominant effect there is no treatment
- PKU = metabolic disorder recessive effect = you only get the disease if you have the two alleles
there is a treatment: diet, newborn baby’s prik makes sense to care about inheritance and
Mendel’s laws
- Scurvy = disorder caused by a single gene in humans. However, we don’t consider calling it a genetic
disorder, why? There is no genetic variation, everyone has that mutation = defective gene
Exception to Mendel’s second law = independent assortment inheritance of one gene is not
affected by the inheritance of another gene
1. law of holds for genes on different chromosomes, for genes that are far apart of the same
chromosome The law does not hold for: genes in proximity on the same chromosome
2. X-linked inheritance = sex-dependent transmission (for example: color blindness)
3. Quantitative trains (complex traits)
,Lecture 2 (2A)
Nurture = experience, environment
Nature = genetics
Extremes of nurture
- John Watson dozen healthy infants, random take one and train him to become any type of
specialist (correct nurture, I can turn you to anything)
- French revolution: born as a blank slate and experience shape you = the good
Bad consequences of extreme nurture view
- Freud’s psychoanalyses
- Noble savage
Extremes of nature
- Konrad Lorenz natural selection determined the evolution of cultures in the same way as it did
that of species (culture that seems better, those are more fit)
- The good/positives about these extremes of nature: better treatment for many diseases and
disorders, critical because there are environmentalism movement, and animal welfare movement
- The bad consequences of extreme nature view: social Darwinism, racism, and eugenics (ras)
Extreme cases are very rare nurture and nature overlap = interesting area
Exceptions to Mendel’s second law quantitative (complex) traits
- two elements
- you get it by polygenic trait = a lot of elements = not caused by single genes
- 1 gene 3 genotypes 3 phenotypes
- increase number of genes more geno and pheno
Qualitative traits influences by a single gene
Quantitative traits influence by multiple genes
Estimating genetic and environmental influences
- adoption study experiment of nurture (biological fam + non-biological fam)
- twin study experiment of nature (raised together + apart)
- family study
Correlation: 0 = no resemblance, 1 = perfect resemblance
Relative risk = change to develop a disorder when a family member has the disorder
Concordance/Discordance = presence/absent of a particular condition in two family members
Adoption studies genetic-plus-environmental relatives
- adoptive parents shared environment (relatives)
- biological parents shared genes (relatives)
PKU = recessive (kid + biological parents by adoption share this because it is genetic)
PKU adoptive parent + kid 0 correlation, because you can’t say anything, because they are not
genetic related
First adoption study
- 47 adopted children with biological mother with schizophrenia 5 kids with schizophrenia
- 47 controls (biological mothers no schizophrenia) 0 kids with schizophrenia
, It has a genetic component
More recent study (adoption study)
- 361 families from Finland, biological mother had schizophrenia kid: 4,9 % schizophrenia and 9,1%
schizophrenia spectrum disorder
- adopted children from mother without 1,1% schizophrenia
genetics plays a role, interaction between genetic vulnerability and environment
What are some potential issues with the adoption design?
- genetic preposition, different environment when you look at it, that’s a lot of nature, but it can
be that the experience can correlate with the genetic preposition
- adoption they try to match the parents’ traits to the kid (same level of intelligence)
they are biased
Issues in adoption studies
- reduction in number of adoptions practical, good thing for society, but not for researchers
- not representative, can’t generalize
- prenatal environment (before they born, they have influence on the biological environment)
- selective placement
Twin studies:
Identical twins single egg fertilized by single sperm, then splits in two = share all genetics
Fraternal twins separate = share half their genes (50%)
How do we know they are twins?
- physical resemblance
- always same sex + same sex chromosomes
- DNA markers
Issues twin studies:
- twin method assumed: environmental is roughly the same for both types of twins reared in the
same family
- But the identical twins experience more similar environment than fraternal twins
- generalizability is an issue for the twin method: are twins’ representative of the general population?
Most evidence suggest a yes
- common environment can be experienced different between twins
Combining adoption and twin studies
Heritability = proportion of phenotypic variance that can be accounted for by genetic differences
among individuals differences in group and related by genetics
A = genetic sharing
C = shared environment
r (correlation) (MZ twins) = A + C
r (DZ twins) = ½ A + C
zie slides!
Heritability is not the same as genetic inheritance
Heritability = about differences between individuals and not about a particular individual
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