Psychobiology
Chapter 2: Genetics and Evolution
- Human Genome Project / Dolly the cloned sheep
o Focus on molecular structure of genes (DNA)
In the Beginning – Evolution
- Darwin → evolution; wrote about origin of species against pro-creationism
o Pro-creationism: god created all species
o Evidence-based approach by Darwin
- Natural selection (slow); ‘survival of the fittest’; selective breeding (quick)
- Evidence for the Theory of Evolution:
o Biogeography: environmental difference of temperature
o Fossil records
o Structural similarity: similar skeletal structures but serve diff. functions
o Embryology: similarities in utero; ontogeny recapitulation of phylogeny (ORP)
o Molecular Biology
- Darwanian good example for: environment changes biology and behavior
- Behavior: individual differences, interpretations, perceptions
The Evolution of Humans
- 600 mill. Years ago: complex water-dwelling organisms
- 150 mill. Years later: bone structures and nerves; vertebrae
- First incarnations of fish ventured onto land → amphibians develop
- Mammals → evolved from reptiles
From Evolution to Genetics
- Behavioral genetics → qualitative and quantitative traits
- Qualitative traits → influenced by single gene; follow simple pattern of inheritance
o Such as Mendelian inheritance
o Phenotypes are qualitatively different; presence/absence of disease
o Unaffected by environment
o Huntington’s disease
o Process not straightforward
o Mosaicism: not all cells genetically identical
§ Turner’s syndrome: deletion of X in some but not all cells
o Phenocopies → disorders caused by epigenetic influences (rubella virus
causing deafness even though DNA is fine)
- Quantitative traits → don’t follow simple patterns of inheritance
o Polygenetic disorders → multiple genes influence a disorder; less predictable
o ADHD → individuals expressing various degrees of symptom severity
o Phenotypic expression → subject to alternation and mitigation
(verminderung) by environmental factors
o Many psychological phenomena and psychological disorders are quantitative
o Quantitative trait loci (QTL) → multiple genes at different locations on the
chromosome contribute to a quantitative trait
1
,Mendelian Genetics
- Account differences in conspecifics → members of same species
o For inheritance, physiological and anatomical characteristics
- Dichotomous traits → characteristics that are in one form or another
o Pea seed either yellow or green → called trait (similar to eye color)
o Yellow seeded plant (Y1) + yellow seeded plant (Y2)= Y1:Y2
o True breeding lines and produce same trait in subsequent generations
- Dominant trait → here the Y1/Y2
- Recessive trait → here green seeds
o 1st generation Y1/Y2 expressed
o 2nd generation g1:g2 produced through carriers (Y1:g1)
- Phenotype → what is observed
- Genotype → what is genetically transmitted
Mendelian Inheritance: Huntington’s Disease
- Mutation in the HTT gene
- Codes protein huntingtin → involves DNA segment CAG
- Dominant allele
PKU: A Recessive Allele
- Phenylketonuria → form of delayed cognitive maturation
- Missing enzyme phenylalanine hydroxylase → needed to break down amino acid
phenylalanine
- Related substances build up and damage CNS → brain damage
- Symptoms: delayed mental and social skills, head size smaller, hyperactivity, jerking
movements of arms and legs
Chromosomes and Inheritance
- Autosome → first 22 chromosomes (excl. sex chromosomes)
- Karyotype → complete set of chromosomes
o 46 chromosomes; 22 identical pairs; 1 set ‘sex’ chromosomes
- Genome → whole of the genetic information of an organism
- Chromosome → long strand of DNA wound around histones
- Telomeres → genetic sequences at the end; protects DNA during cell division
- Cytogenetic bands → stripes on chromosomes (staining technique)
- Meiosis → cellular division
- Crossing over → during meiosis; different genetic information on chromatids
DNA – Deoxyribonucleic acid
- 1. Replicates itself to make new cells
- 2. Makes proteins and determines function of cell
- Proteins → make up 50% weight of dry cell
- Each chromosome = 2 strands of DNA
- DNA → carbon, sugar (ribose), nitrogenous base, phosphate group
- Nitrogenous bases → adenine, cytosine, guanine, thymine (p. 45)
o Adenine + thymine
2
, o Cytosine + guanine
Function of DNA
- Replication
- Protein synthesis
o Amino acids → codon (three nucleotids)
o Reading DNA → transcription
§ Creation of messenger ribonucleic acid (mRNA)
§ Carries code from nucleus to cytoplasm
§ mRNA not exact copy → uracil substitutes for thymine
§ three-nucleotide bases are specifying an amino acid
• if it goes wrong → sickle cell disease (e.g.); abnormal
heamoglobin → CAT (GUA) instead of CTT (GAA)
§ Exons → base sequences that code for proteins
§ Introns → noncoding sequences
§ Ribosomes are the translators
§ Transfer ribonucleic acid (tRNA) → take amino acid to ribosome
- Genetic Variation
o Polymorphism → differences in DNA among individuals
o Larger Polymorphism → single nucleotide polymorphisms (SNPs)
§ Each SNP represents a difference in a single nucleotide
§ No clear pattern of inheritance; only vulnerability not disorder itself
- Variable Number and Tandem Repeat
o Tandem repeat → repeated duplication of a core DNA sequence
§ Minisatellites → 2-4 base pairs
o Insertions (deletions) → loss/addition of 1 or more nucleotides; changes in
chromosome numbers
§ Deletions occur during meiosis; piece of chromosome breaks off; not
having full complement DNA
§ Results in neurodevelopmental disorder Williams-Beuren syndrome
• Deletion of chromosome 7
o Inversions → segments of chromosome turned round by 180°
§ Show no phenotypic abnormalities
o Translocations → balanced (equal parts of two chromosomes exchanged);
unbalanced (unequal proportions and leads to extra/missing genes)
o Monosomy → only one particular type of chromosome (Turner’s syndrome)
o Polyploid → more than two sets of chromosomes
- Biotechnology: polymerase chain reaction (PCR)
o Copies a known sequence of DNA; allows multiple copies to be made
o Electrophoresis → agarose gel block; DNA negatively charged; gel positively
charged
Epigenetics
- Functional modifications of the genome; no change in DNA
3
, Behavioral Genetics: Complex Interplay of Psychology and Genetics
- Nature-nurture debate
- Twin studies; familial studies
- Heritability → 1 (entirely attributable to genetics); 0 (caused by environmental
factors)
o Commonly → 0.5
o Schizophrenia → 0.75 genetic; 0.25 environmental
o Height → highly heritable 0.88
- Twin studies → close degree of genetic similarity between offspring, siblings, parents
- Turkheimer → 3 laws of behavioral genetics
o 1. All human behavioral traits are heritable
o 2. Effect of being raised in the same family is smaller than effect of genes
o 3. Variation in complex human behavioral traits not accounted for by the
effect of genes/families
- Adoption studies
- Virtual twins → share same rearing practices; estimate of environmental factors
DNA and Psychology
- Candidate genes → any gene thought likely to cause disease
Beyond Mendelian Inheritance: The Endophenotype
- Most disorders → complex polygenetic disorders
- Endophenotype → intermediate account of genes and environment
o Genes likely to cause disorder (e.g. ADHD) and the symptoms (e.g.
impulsivity) → theoretical account of the disorder (e.g. faulty behavioral
inhibition) that links physical (gene/brain) to the behavioral
o 1. Endophenotype associated with illness in population
o 2. Endophenotype is heritable
o 3. EPT is primarily state independent → manifest itself in an individual
whether or not they are symptomatic
o 4. Within families EPT and the disorder co-occur
o 5. EPT in affected family members found in non-affected family members at a
higher rate than in the general population
Human Genome Project
- 3.2 billion chemical nucleotide base pairs (A, C, T, G)
- 20,000-25,000 protein coding genes (80,000-140,000 estimated)
- 99.9% in all people is same sequence
- 2% of genome encodes instructions for synthesis of proteins
- 50% of sequences don’t code for proteins
- G, C gene-dense → A, T gene-poor
4
Chapter 2: Genetics and Evolution
- Human Genome Project / Dolly the cloned sheep
o Focus on molecular structure of genes (DNA)
In the Beginning – Evolution
- Darwin → evolution; wrote about origin of species against pro-creationism
o Pro-creationism: god created all species
o Evidence-based approach by Darwin
- Natural selection (slow); ‘survival of the fittest’; selective breeding (quick)
- Evidence for the Theory of Evolution:
o Biogeography: environmental difference of temperature
o Fossil records
o Structural similarity: similar skeletal structures but serve diff. functions
o Embryology: similarities in utero; ontogeny recapitulation of phylogeny (ORP)
o Molecular Biology
- Darwanian good example for: environment changes biology and behavior
- Behavior: individual differences, interpretations, perceptions
The Evolution of Humans
- 600 mill. Years ago: complex water-dwelling organisms
- 150 mill. Years later: bone structures and nerves; vertebrae
- First incarnations of fish ventured onto land → amphibians develop
- Mammals → evolved from reptiles
From Evolution to Genetics
- Behavioral genetics → qualitative and quantitative traits
- Qualitative traits → influenced by single gene; follow simple pattern of inheritance
o Such as Mendelian inheritance
o Phenotypes are qualitatively different; presence/absence of disease
o Unaffected by environment
o Huntington’s disease
o Process not straightforward
o Mosaicism: not all cells genetically identical
§ Turner’s syndrome: deletion of X in some but not all cells
o Phenocopies → disorders caused by epigenetic influences (rubella virus
causing deafness even though DNA is fine)
- Quantitative traits → don’t follow simple patterns of inheritance
o Polygenetic disorders → multiple genes influence a disorder; less predictable
o ADHD → individuals expressing various degrees of symptom severity
o Phenotypic expression → subject to alternation and mitigation
(verminderung) by environmental factors
o Many psychological phenomena and psychological disorders are quantitative
o Quantitative trait loci (QTL) → multiple genes at different locations on the
chromosome contribute to a quantitative trait
1
,Mendelian Genetics
- Account differences in conspecifics → members of same species
o For inheritance, physiological and anatomical characteristics
- Dichotomous traits → characteristics that are in one form or another
o Pea seed either yellow or green → called trait (similar to eye color)
o Yellow seeded plant (Y1) + yellow seeded plant (Y2)= Y1:Y2
o True breeding lines and produce same trait in subsequent generations
- Dominant trait → here the Y1/Y2
- Recessive trait → here green seeds
o 1st generation Y1/Y2 expressed
o 2nd generation g1:g2 produced through carriers (Y1:g1)
- Phenotype → what is observed
- Genotype → what is genetically transmitted
Mendelian Inheritance: Huntington’s Disease
- Mutation in the HTT gene
- Codes protein huntingtin → involves DNA segment CAG
- Dominant allele
PKU: A Recessive Allele
- Phenylketonuria → form of delayed cognitive maturation
- Missing enzyme phenylalanine hydroxylase → needed to break down amino acid
phenylalanine
- Related substances build up and damage CNS → brain damage
- Symptoms: delayed mental and social skills, head size smaller, hyperactivity, jerking
movements of arms and legs
Chromosomes and Inheritance
- Autosome → first 22 chromosomes (excl. sex chromosomes)
- Karyotype → complete set of chromosomes
o 46 chromosomes; 22 identical pairs; 1 set ‘sex’ chromosomes
- Genome → whole of the genetic information of an organism
- Chromosome → long strand of DNA wound around histones
- Telomeres → genetic sequences at the end; protects DNA during cell division
- Cytogenetic bands → stripes on chromosomes (staining technique)
- Meiosis → cellular division
- Crossing over → during meiosis; different genetic information on chromatids
DNA – Deoxyribonucleic acid
- 1. Replicates itself to make new cells
- 2. Makes proteins and determines function of cell
- Proteins → make up 50% weight of dry cell
- Each chromosome = 2 strands of DNA
- DNA → carbon, sugar (ribose), nitrogenous base, phosphate group
- Nitrogenous bases → adenine, cytosine, guanine, thymine (p. 45)
o Adenine + thymine
2
, o Cytosine + guanine
Function of DNA
- Replication
- Protein synthesis
o Amino acids → codon (three nucleotids)
o Reading DNA → transcription
§ Creation of messenger ribonucleic acid (mRNA)
§ Carries code from nucleus to cytoplasm
§ mRNA not exact copy → uracil substitutes for thymine
§ three-nucleotide bases are specifying an amino acid
• if it goes wrong → sickle cell disease (e.g.); abnormal
heamoglobin → CAT (GUA) instead of CTT (GAA)
§ Exons → base sequences that code for proteins
§ Introns → noncoding sequences
§ Ribosomes are the translators
§ Transfer ribonucleic acid (tRNA) → take amino acid to ribosome
- Genetic Variation
o Polymorphism → differences in DNA among individuals
o Larger Polymorphism → single nucleotide polymorphisms (SNPs)
§ Each SNP represents a difference in a single nucleotide
§ No clear pattern of inheritance; only vulnerability not disorder itself
- Variable Number and Tandem Repeat
o Tandem repeat → repeated duplication of a core DNA sequence
§ Minisatellites → 2-4 base pairs
o Insertions (deletions) → loss/addition of 1 or more nucleotides; changes in
chromosome numbers
§ Deletions occur during meiosis; piece of chromosome breaks off; not
having full complement DNA
§ Results in neurodevelopmental disorder Williams-Beuren syndrome
• Deletion of chromosome 7
o Inversions → segments of chromosome turned round by 180°
§ Show no phenotypic abnormalities
o Translocations → balanced (equal parts of two chromosomes exchanged);
unbalanced (unequal proportions and leads to extra/missing genes)
o Monosomy → only one particular type of chromosome (Turner’s syndrome)
o Polyploid → more than two sets of chromosomes
- Biotechnology: polymerase chain reaction (PCR)
o Copies a known sequence of DNA; allows multiple copies to be made
o Electrophoresis → agarose gel block; DNA negatively charged; gel positively
charged
Epigenetics
- Functional modifications of the genome; no change in DNA
3
, Behavioral Genetics: Complex Interplay of Psychology and Genetics
- Nature-nurture debate
- Twin studies; familial studies
- Heritability → 1 (entirely attributable to genetics); 0 (caused by environmental
factors)
o Commonly → 0.5
o Schizophrenia → 0.75 genetic; 0.25 environmental
o Height → highly heritable 0.88
- Twin studies → close degree of genetic similarity between offspring, siblings, parents
- Turkheimer → 3 laws of behavioral genetics
o 1. All human behavioral traits are heritable
o 2. Effect of being raised in the same family is smaller than effect of genes
o 3. Variation in complex human behavioral traits not accounted for by the
effect of genes/families
- Adoption studies
- Virtual twins → share same rearing practices; estimate of environmental factors
DNA and Psychology
- Candidate genes → any gene thought likely to cause disease
Beyond Mendelian Inheritance: The Endophenotype
- Most disorders → complex polygenetic disorders
- Endophenotype → intermediate account of genes and environment
o Genes likely to cause disorder (e.g. ADHD) and the symptoms (e.g.
impulsivity) → theoretical account of the disorder (e.g. faulty behavioral
inhibition) that links physical (gene/brain) to the behavioral
o 1. Endophenotype associated with illness in population
o 2. Endophenotype is heritable
o 3. EPT is primarily state independent → manifest itself in an individual
whether or not they are symptomatic
o 4. Within families EPT and the disorder co-occur
o 5. EPT in affected family members found in non-affected family members at a
higher rate than in the general population
Human Genome Project
- 3.2 billion chemical nucleotide base pairs (A, C, T, G)
- 20,000-25,000 protein coding genes (80,000-140,000 estimated)
- 99.9% in all people is same sequence
- 2% of genome encodes instructions for synthesis of proteins
- 50% of sequences don’t code for proteins
- G, C gene-dense → A, T gene-poor
4
