Behavioral genetics notes
Inhoud
Behavioral genetics notes.......................................................................................................................1
Lecture 1. 29/10/2025........................................................................................................................3
Lecture 2. 30/10/2025........................................................................................................................5
Lecture 3. 5/11/2025........................................................................................................................12
Lecture 4. 6/11/2025........................................................................................................................15
Lecture 5. 12/11/2025......................................................................................................................18
Lecture 6. 13/11/2025......................................................................................................................20
Lecture 7. 19/11/2025......................................................................................................................22
Videolectures 7. 19/11/2025............................................................................................................24
Lecture 8. 20/11/2025......................................................................................................................27
Lecture 9. 26/11/2025......................................................................................................................28
Lecture 10. 27/11/2025....................................................................................................................31
Lecture 11. 03/12/2025....................................................................................................................34
Lecture 12. 04/12/2025....................................................................................................................37
Lecture 13. 10/12/2025....................................................................................................................41
Lecture 14. 11/12/2025....................................................................................................................47
Chapter 2..............................................................................................................................................49
Chapter 3..............................................................................................................................................50
Chapter 4..............................................................................................................................................51
Chapter 9..............................................................................................................................................52
Chapter 7..............................................................................................................................................53
Chapter 6..............................................................................................................................................54
Chapter 8..............................................................................................................................................55
Chapter 10............................................................................................................................................56
Chapter 17............................................................................................................................................57
Chapter 13............................................................................................................................................58
Chapter 14............................................................................................................................................59
Chapter 15............................................................................................................................................60
Chapter 12............................................................................................................................................61
Chapter 11............................................................................................................................................63
Chapter 16............................................................................................................................................64
Chapter 18............................................................................................................................................65
,Chapter 19............................................................................................................................................66
Chapter 20............................................................................................................................................67
,Lecture 1. 29/10/2025
Historical perspective
Ancient world: parents pass on characteristics to offspring.
o Silly belief from ancient Greeks: Aristotle thought children were made from
“purified blood from the testes”(semen) and menstrual blood.
From menstrual blood, because he saw that women stopped
bleeding when getting pregnant that blood is now going into the
foetus.
Antonie van Leeuwenhoek (1632-1723) and Nicolaas Hartsoeker (1656-1725)
invented the microscope and started the field of microbiology
o Developed/ refined the theory of preformationism: we all come from
miniature versions of ourselves. Sperm contains complete preformed
individuals (“homunculus”) .
Flaws to that theory:
1. The mother’s characteristics won’t come through, since the whole
thing is in the sperm cell.
2. Pregnancy gets downplayed in this theory.
3. The homunculus is there, but for the grandkid it is already there,
you need the sperm inside the sperm inside the sperm inside the
sperm… big/infinite number of sperm in there to pass on.
Francis Galton (1822-1911)
o Galton found psychometrics (science of measuring mental faculties),
differential psychology and behavior genetics.
o He studied family trees (pedigree) to understand hereditary/ genetic
influences.
o Galton analysed the tendency of twin pairs to be more alike or different
over time.
o “eminent status” was more likely to appear in close relatives, with the
likelihood of eminence decreasing as the degree of relationship became
more remote.
Galton: “nature prevails enormously over nurture”.
o Galton was still rooted by 19th century Victorian society: racist and classist
Its remarkable the extent to which Galton was willing to accept
family clustering as evidence of nature.
Galton tried to consider the role of the environment. But he was
firmly rooted in the confines of the 19th century: pre-genetic,
intensely racist and rigidly stratified society. So much that he could
not fully appreciate the magnitude of the problem
Besides, Galton did not have the scientific tools and statistics for it.
He did not use the twin method in what we now think of in the
“classical” way, via comparison of the similarity of monozygotic and
dizygotic twins.
Charles Darwin (1809-1882)
o His work forever changed all research fields that deal with life on earth –
from biochemistry to social psychology.
o Theory of evolution: all species arose through the natural selection of
small, inherited variations that increase the individual’s ability to survive
and reproduce.
, o The idea of blending inheritance: though Darwin was on the right track
about many things, he was terribly off track about the mechanism behind
inheritance. As were everyone else before Mendel.
o Charles Darwin’s theory of pangenesis: contributions to egg or sperm from
every part of the body. And it implied blended inheritance.
Kids are the average of the blended traits of their parents.
o Problem of blending theories of inheritance: for natural selection you need
diversity. If everyone is the same, there is nothing to select from, so no
change, no evolution if inheritance always blends stuff.
Gregor Mendel (1822-1884)
o Monk, experimented with plants and combining
seeds of peas and tried to breed them until the
peas were smooth (instead of wrinkled).
o With 2 populations and combining it (smooth and
wrinkled) it will get a little smooth or a little
wrinkled.
o You pass on two things:
SS (S = dominant) and ss ¼ SS; ½ Ss; ¼
ss.
Mendel’s laws:
1. The law of segregation
a. There are:
1. Two elements of heredity for each trait in each individual.
2. These two elements separate or segregate, during reproduction.
3. Offspring receives one of the two elements from each parent.
b. This law finally ended the theories of blended inheritance.
c. Punnett square: diagram used to predict the genotypes of a cross or
breeding experiment. Useful to determine the probability of an offspring
having a particular genotype.
d. Dominant allele (S): an allele that expresses its phenotypic effect even
when heterozygous with a recessive allele. So, if S is dominant over s, then
SS and Ss have the same phenotype.
e. Recessive allele (s): an allele whose phenotypic effect is not expressed in a
heterozygote.
i. Homozygosity: 2 the same alleles at a locus.
ii. Heterozygosity: 2 different alleles at a locus.
2. The law of independent assortment
a. The inheritance pattern of one trait will not affect the inheritance pattern of
another.
Mendelian traits/disorders (single-gene mutations changing a person)
1. Huntington’s disease
a. Brain disorder causing progressive deterioration of brain cells that leads to
severe incapacitation and eventual death.
b. Symptoms: uncontrollable movements, abnormal balance when walking,
slurred speech, thinking difficulties and personality changes.
c. There’s no cure and no effective treatment.
Discovery of the disease by George Huntington in 1892; discovery of the genetic
basis by an international collaboration in 1993.
Inhoud
Behavioral genetics notes.......................................................................................................................1
Lecture 1. 29/10/2025........................................................................................................................3
Lecture 2. 30/10/2025........................................................................................................................5
Lecture 3. 5/11/2025........................................................................................................................12
Lecture 4. 6/11/2025........................................................................................................................15
Lecture 5. 12/11/2025......................................................................................................................18
Lecture 6. 13/11/2025......................................................................................................................20
Lecture 7. 19/11/2025......................................................................................................................22
Videolectures 7. 19/11/2025............................................................................................................24
Lecture 8. 20/11/2025......................................................................................................................27
Lecture 9. 26/11/2025......................................................................................................................28
Lecture 10. 27/11/2025....................................................................................................................31
Lecture 11. 03/12/2025....................................................................................................................34
Lecture 12. 04/12/2025....................................................................................................................37
Lecture 13. 10/12/2025....................................................................................................................41
Lecture 14. 11/12/2025....................................................................................................................47
Chapter 2..............................................................................................................................................49
Chapter 3..............................................................................................................................................50
Chapter 4..............................................................................................................................................51
Chapter 9..............................................................................................................................................52
Chapter 7..............................................................................................................................................53
Chapter 6..............................................................................................................................................54
Chapter 8..............................................................................................................................................55
Chapter 10............................................................................................................................................56
Chapter 17............................................................................................................................................57
Chapter 13............................................................................................................................................58
Chapter 14............................................................................................................................................59
Chapter 15............................................................................................................................................60
Chapter 12............................................................................................................................................61
Chapter 11............................................................................................................................................63
Chapter 16............................................................................................................................................64
Chapter 18............................................................................................................................................65
,Chapter 19............................................................................................................................................66
Chapter 20............................................................................................................................................67
,Lecture 1. 29/10/2025
Historical perspective
Ancient world: parents pass on characteristics to offspring.
o Silly belief from ancient Greeks: Aristotle thought children were made from
“purified blood from the testes”(semen) and menstrual blood.
From menstrual blood, because he saw that women stopped
bleeding when getting pregnant that blood is now going into the
foetus.
Antonie van Leeuwenhoek (1632-1723) and Nicolaas Hartsoeker (1656-1725)
invented the microscope and started the field of microbiology
o Developed/ refined the theory of preformationism: we all come from
miniature versions of ourselves. Sperm contains complete preformed
individuals (“homunculus”) .
Flaws to that theory:
1. The mother’s characteristics won’t come through, since the whole
thing is in the sperm cell.
2. Pregnancy gets downplayed in this theory.
3. The homunculus is there, but for the grandkid it is already there,
you need the sperm inside the sperm inside the sperm inside the
sperm… big/infinite number of sperm in there to pass on.
Francis Galton (1822-1911)
o Galton found psychometrics (science of measuring mental faculties),
differential psychology and behavior genetics.
o He studied family trees (pedigree) to understand hereditary/ genetic
influences.
o Galton analysed the tendency of twin pairs to be more alike or different
over time.
o “eminent status” was more likely to appear in close relatives, with the
likelihood of eminence decreasing as the degree of relationship became
more remote.
Galton: “nature prevails enormously over nurture”.
o Galton was still rooted by 19th century Victorian society: racist and classist
Its remarkable the extent to which Galton was willing to accept
family clustering as evidence of nature.
Galton tried to consider the role of the environment. But he was
firmly rooted in the confines of the 19th century: pre-genetic,
intensely racist and rigidly stratified society. So much that he could
not fully appreciate the magnitude of the problem
Besides, Galton did not have the scientific tools and statistics for it.
He did not use the twin method in what we now think of in the
“classical” way, via comparison of the similarity of monozygotic and
dizygotic twins.
Charles Darwin (1809-1882)
o His work forever changed all research fields that deal with life on earth –
from biochemistry to social psychology.
o Theory of evolution: all species arose through the natural selection of
small, inherited variations that increase the individual’s ability to survive
and reproduce.
, o The idea of blending inheritance: though Darwin was on the right track
about many things, he was terribly off track about the mechanism behind
inheritance. As were everyone else before Mendel.
o Charles Darwin’s theory of pangenesis: contributions to egg or sperm from
every part of the body. And it implied blended inheritance.
Kids are the average of the blended traits of their parents.
o Problem of blending theories of inheritance: for natural selection you need
diversity. If everyone is the same, there is nothing to select from, so no
change, no evolution if inheritance always blends stuff.
Gregor Mendel (1822-1884)
o Monk, experimented with plants and combining
seeds of peas and tried to breed them until the
peas were smooth (instead of wrinkled).
o With 2 populations and combining it (smooth and
wrinkled) it will get a little smooth or a little
wrinkled.
o You pass on two things:
SS (S = dominant) and ss ¼ SS; ½ Ss; ¼
ss.
Mendel’s laws:
1. The law of segregation
a. There are:
1. Two elements of heredity for each trait in each individual.
2. These two elements separate or segregate, during reproduction.
3. Offspring receives one of the two elements from each parent.
b. This law finally ended the theories of blended inheritance.
c. Punnett square: diagram used to predict the genotypes of a cross or
breeding experiment. Useful to determine the probability of an offspring
having a particular genotype.
d. Dominant allele (S): an allele that expresses its phenotypic effect even
when heterozygous with a recessive allele. So, if S is dominant over s, then
SS and Ss have the same phenotype.
e. Recessive allele (s): an allele whose phenotypic effect is not expressed in a
heterozygote.
i. Homozygosity: 2 the same alleles at a locus.
ii. Heterozygosity: 2 different alleles at a locus.
2. The law of independent assortment
a. The inheritance pattern of one trait will not affect the inheritance pattern of
another.
Mendelian traits/disorders (single-gene mutations changing a person)
1. Huntington’s disease
a. Brain disorder causing progressive deterioration of brain cells that leads to
severe incapacitation and eventual death.
b. Symptoms: uncontrollable movements, abnormal balance when walking,
slurred speech, thinking difficulties and personality changes.
c. There’s no cure and no effective treatment.
Discovery of the disease by George Huntington in 1892; discovery of the genetic
basis by an international collaboration in 1993.
