Mattering and History
(1) Behavioural genetics
Continues to flow beyond psychology and psychiatry into other fields:
● Neuroscience
● Economics
● Political science
● Education
● Sociology
Adding genetics in a research study is now easier (using saliva), cheaper (cost of genotyping) and has
better statistical tools (eg GWAS and polygenic scores)
In the ancient world, it was discussed by Pythagoras and Aristotle that parents pass on characteristics
to offspring
● Pythagoras suggested that the father supplies the essential characteristics (“form”) and the
mother supplies the material building blocks
● Aristotle thought children were made from “purified blood from the testes” (semen) and
menstrual blood
Consequences of genetics:
● Upon learning that they have elevated genetic risks for a mental disorder (eg depression),
people may become more pessimistic about their prognosis and misremember their symptoms
as being more serious because they misconceive genes as immutable and defining of their
identity
● Upon learning that they are not genetically predisposed to a mental disorder (eg alcohol use
disorder), people may underplay the downstream ramifications of the symptoms even when
they are currently experiencing those symptoms.
However,
● Researchers in the life sciences, mind sciences, and social sciences can use genetics as a
control/correction to detect the truth (and to know the real harm and benefits of a policy or
drug or therapy)
● Polygenic predictors will be key to personalised genomics, which hopes to predict risk,
identify treatment interactions, and propose interventions to prevent problems before they
appear.
,Antonie van Leeuwenheok (1632-1723), Nicolaas Hartsoeker (1656 - 1725)
Theory of Preformationism: we all come from miniature versions of ourselves. Sperm contain
completely preformed individuals called “homunculus"
● vs Epigenesis: the growth of an egg cell from an animal, or seed from a plant that develops in
stages to finally produce a complex organism
Francis Galton (1822 - 1911): father of behavioural genetics
● Founded psychometrics: the science of measuring mental faculties
● Founded differential psychology and behavioural genetics
● Studied twins and family trees (pedigree) to understand hereditary/genetic influences
● Believed nature prevailed enormously over nurture → “eminent status” was more likely to
appear in close relatives, with the likelihood of eminence decreasing as the degree of
relationship became more remote
Charles Darwin (1908-1882)
● Heretical theory: species evolve one from another
● Theory of evolution begins with variation within a population partially due to heredity → can
be summarised as “all species arose through the natural selection of small, inherited variations
that increase the individual's ability to survive and reproduce”
○ If the likelihood of surviving and reproducing (because survival is not enough) is
influenced partially due to a slight degree by a particular trait, the offspring of the
survivors will show more of the trait to a point those changes are so great that
populations become different species
○ Hence, 1. It is difficult to know the main mechanism driving evolutionary changes
2. Although behaviour is not as well preserver as physical characteristics, it is
likely that behaviour is often at the cutting edge of natural selection
● Theory of pangenesis: contributions to egg or sperm from every part of the body, implied
blending inheritance
○ Blending inheritance: the theory is that the progeny inherits any characteristic as the
average of the parents' values of that characteristic
, Mendel’s Laws and Exceptions to the 2nd Law
(1) Mendel’s Laws
Pedigrees: a diagram of family history that uses standardised symbols
1.1 First law of heredity
Law of segregation: alleles segregate randomly into gametes. When gametes are formed, each allele
of one parent segregates randomly into the gametes, such that half of the parent's gametes carry each
allele
● One of these genes can “dominate”, the non-dominant (recessive) is only expressed if both
genes are recessive
● Alleles: alternative form or versions of a gene
○ Combination of these alleles is called genotype and it determines the phenotype (the
observed traits)
Punnett Square: diagram used to predict genotypes of a cross or breeding experiment
● Dominant allele (upper case): An allele that expresses its phenotypic effect even when
heterozygous with a recessive allele
● Recessive allele (lower case): An allele whose phenotypic effect is not expressed in a
heterozygote, it is only expressed when homozygous
Hardy-Weinberg equilibrium (HWE): genotype and allele frequencies in a population remain constant
between generations in the absence of disturbance by outside factors (eg natural selection, migration)
● Population genetics: a study of the forces that change allele frequency
, P q
P 𝑃
2 𝑃𝑞
q 𝑃𝑞 𝑞
2
● If you have two identical alleles (homozygous), the chances of fertilisation with p² or q² are
there. For example, having two dominant alleles (like PP) or two recessive alleles (like qq)
● Chances of Heterozygous Offspring: now, if you have one of each allele (heterozygous, like
Pq), the chances are 2pq
● If you were to predict the genotypes of the offspring, you'd add up the possibilities → p² +
2pq + q² = 1
Mendel’s Conclusion:
● Two ‘elements’/genes of heredity for each trait in each individual
● These two elements separate during reproduction and offspring receive one of the two
elements from each parent
1.2 Second Law of Heredity
Law of Independent Assortment: the inheritance pattern of one trait will not affect the inheritance
pattern of another
Crossed true-breeding parents that showed the dominant trait for both A and B with parents that
showed the recessive forms for A and B. He found second-generation (F2) offspring of all four
possible types with the expected frequencies if A and B were inherited independently:
● Dominant for A and B (AB)
● Dominant for A and recessive for B (Ab)
● Recessive for A and dominant for B (aB)
● And recessive for A and B (ab)
Note: Mendel’s law is violated when genes for two traits are close together on the same chromosome
→ these violations make it possible to map genes to chromosomes
(1) Behavioural genetics
Continues to flow beyond psychology and psychiatry into other fields:
● Neuroscience
● Economics
● Political science
● Education
● Sociology
Adding genetics in a research study is now easier (using saliva), cheaper (cost of genotyping) and has
better statistical tools (eg GWAS and polygenic scores)
In the ancient world, it was discussed by Pythagoras and Aristotle that parents pass on characteristics
to offspring
● Pythagoras suggested that the father supplies the essential characteristics (“form”) and the
mother supplies the material building blocks
● Aristotle thought children were made from “purified blood from the testes” (semen) and
menstrual blood
Consequences of genetics:
● Upon learning that they have elevated genetic risks for a mental disorder (eg depression),
people may become more pessimistic about their prognosis and misremember their symptoms
as being more serious because they misconceive genes as immutable and defining of their
identity
● Upon learning that they are not genetically predisposed to a mental disorder (eg alcohol use
disorder), people may underplay the downstream ramifications of the symptoms even when
they are currently experiencing those symptoms.
However,
● Researchers in the life sciences, mind sciences, and social sciences can use genetics as a
control/correction to detect the truth (and to know the real harm and benefits of a policy or
drug or therapy)
● Polygenic predictors will be key to personalised genomics, which hopes to predict risk,
identify treatment interactions, and propose interventions to prevent problems before they
appear.
,Antonie van Leeuwenheok (1632-1723), Nicolaas Hartsoeker (1656 - 1725)
Theory of Preformationism: we all come from miniature versions of ourselves. Sperm contain
completely preformed individuals called “homunculus"
● vs Epigenesis: the growth of an egg cell from an animal, or seed from a plant that develops in
stages to finally produce a complex organism
Francis Galton (1822 - 1911): father of behavioural genetics
● Founded psychometrics: the science of measuring mental faculties
● Founded differential psychology and behavioural genetics
● Studied twins and family trees (pedigree) to understand hereditary/genetic influences
● Believed nature prevailed enormously over nurture → “eminent status” was more likely to
appear in close relatives, with the likelihood of eminence decreasing as the degree of
relationship became more remote
Charles Darwin (1908-1882)
● Heretical theory: species evolve one from another
● Theory of evolution begins with variation within a population partially due to heredity → can
be summarised as “all species arose through the natural selection of small, inherited variations
that increase the individual's ability to survive and reproduce”
○ If the likelihood of surviving and reproducing (because survival is not enough) is
influenced partially due to a slight degree by a particular trait, the offspring of the
survivors will show more of the trait to a point those changes are so great that
populations become different species
○ Hence, 1. It is difficult to know the main mechanism driving evolutionary changes
2. Although behaviour is not as well preserver as physical characteristics, it is
likely that behaviour is often at the cutting edge of natural selection
● Theory of pangenesis: contributions to egg or sperm from every part of the body, implied
blending inheritance
○ Blending inheritance: the theory is that the progeny inherits any characteristic as the
average of the parents' values of that characteristic
, Mendel’s Laws and Exceptions to the 2nd Law
(1) Mendel’s Laws
Pedigrees: a diagram of family history that uses standardised symbols
1.1 First law of heredity
Law of segregation: alleles segregate randomly into gametes. When gametes are formed, each allele
of one parent segregates randomly into the gametes, such that half of the parent's gametes carry each
allele
● One of these genes can “dominate”, the non-dominant (recessive) is only expressed if both
genes are recessive
● Alleles: alternative form or versions of a gene
○ Combination of these alleles is called genotype and it determines the phenotype (the
observed traits)
Punnett Square: diagram used to predict genotypes of a cross or breeding experiment
● Dominant allele (upper case): An allele that expresses its phenotypic effect even when
heterozygous with a recessive allele
● Recessive allele (lower case): An allele whose phenotypic effect is not expressed in a
heterozygote, it is only expressed when homozygous
Hardy-Weinberg equilibrium (HWE): genotype and allele frequencies in a population remain constant
between generations in the absence of disturbance by outside factors (eg natural selection, migration)
● Population genetics: a study of the forces that change allele frequency
, P q
P 𝑃
2 𝑃𝑞
q 𝑃𝑞 𝑞
2
● If you have two identical alleles (homozygous), the chances of fertilisation with p² or q² are
there. For example, having two dominant alleles (like PP) or two recessive alleles (like qq)
● Chances of Heterozygous Offspring: now, if you have one of each allele (heterozygous, like
Pq), the chances are 2pq
● If you were to predict the genotypes of the offspring, you'd add up the possibilities → p² +
2pq + q² = 1
Mendel’s Conclusion:
● Two ‘elements’/genes of heredity for each trait in each individual
● These two elements separate during reproduction and offspring receive one of the two
elements from each parent
1.2 Second Law of Heredity
Law of Independent Assortment: the inheritance pattern of one trait will not affect the inheritance
pattern of another
Crossed true-breeding parents that showed the dominant trait for both A and B with parents that
showed the recessive forms for A and B. He found second-generation (F2) offspring of all four
possible types with the expected frequencies if A and B were inherited independently:
● Dominant for A and B (AB)
● Dominant for A and recessive for B (Ab)
● Recessive for A and dominant for B (aB)
● And recessive for A and B (ab)
Note: Mendel’s law is violated when genes for two traits are close together on the same chromosome
→ these violations make it possible to map genes to chromosomes
