PSYCH1000: CHAPTER 4: GENES, EVOLUTION &
BEHAVIOUR
Genetic Influences
• Hereditary potential
• 23 chromosome pairs: carry genes: containing DNA: which codes for RNA: which
synthesizes proteins
• Protein production influences development, structure, function
• Genotypes vs Phenotypes
• Genotype: genetic makeup (set of genes inherited)
• Phenotype: observable expression of genotypes (characteristics produced)
• Not necessarily identical —> genes can be dominant or recessive
• Cannot infer genotype from phenotype
• Polygenic Transmission
• Phenotype influenced by more than 1 gene pair / chromosome
• Can be calculated using heritability?
How do genes work (gene action)?
• Genes are strand-like molecules of DNA linked on chromosomes
• Karyotype: genetic blueprint showing all pairs of chromosomes
• Humans have 22 autosomes and 1 pair of sex chromosomes per cell for 23 total (except in
sex cells)
• Gene doesn’t directly relate to an attribute, but they affect it through protein synthesis
• Critical period: genetically programmed trait that requires environmental exposure in order to
be “activated”
• Alleles: possible forms of a gene (dominant or recessive)
• Homozygous alleles: matching (phenotypic outcome predictable)
• Dominant: produces affect in either homo or hetero mode
• Recessive: only produces effect in homozygous mode (where both are recessive)
• Incomplete dominance: phenotypic expression is a blend of dominant/recessive trait
• Co-dominance: both phenotypic traits expressed fully
Nurture AND Nature: influence of Environment
• Environment also impacts protein synthesis
• Genes determine range of possibilities, but not degree of expression
REMEMBER: environment can alter things that seem to be internally coded traits
EPIGENETICS
Heritability
• Estimate —> how much observed variability is due to genetic factors alone? (in a group)
• (Variance due to genes) / (total variance)
• Applies to groups NOT individuals
• No variability —> no heritability (if there’s no variance, you can’t calculate heritability)
• Genetic diversity increases —> heritability increases (closer to 1)
• Environmental diversity increases —> heritability decreases (closer to 0)
• Uses identical twins to determine number
• Important assumption: no environmental differences for identical vs fraternal twins
h 2 = 0 —> due to environment
h 2 = 1 —> due to genes
Behaviour Genetics Techniques
BEHAVIOUR
Genetic Influences
• Hereditary potential
• 23 chromosome pairs: carry genes: containing DNA: which codes for RNA: which
synthesizes proteins
• Protein production influences development, structure, function
• Genotypes vs Phenotypes
• Genotype: genetic makeup (set of genes inherited)
• Phenotype: observable expression of genotypes (characteristics produced)
• Not necessarily identical —> genes can be dominant or recessive
• Cannot infer genotype from phenotype
• Polygenic Transmission
• Phenotype influenced by more than 1 gene pair / chromosome
• Can be calculated using heritability?
How do genes work (gene action)?
• Genes are strand-like molecules of DNA linked on chromosomes
• Karyotype: genetic blueprint showing all pairs of chromosomes
• Humans have 22 autosomes and 1 pair of sex chromosomes per cell for 23 total (except in
sex cells)
• Gene doesn’t directly relate to an attribute, but they affect it through protein synthesis
• Critical period: genetically programmed trait that requires environmental exposure in order to
be “activated”
• Alleles: possible forms of a gene (dominant or recessive)
• Homozygous alleles: matching (phenotypic outcome predictable)
• Dominant: produces affect in either homo or hetero mode
• Recessive: only produces effect in homozygous mode (where both are recessive)
• Incomplete dominance: phenotypic expression is a blend of dominant/recessive trait
• Co-dominance: both phenotypic traits expressed fully
Nurture AND Nature: influence of Environment
• Environment also impacts protein synthesis
• Genes determine range of possibilities, but not degree of expression
REMEMBER: environment can alter things that seem to be internally coded traits
EPIGENETICS
Heritability
• Estimate —> how much observed variability is due to genetic factors alone? (in a group)
• (Variance due to genes) / (total variance)
• Applies to groups NOT individuals
• No variability —> no heritability (if there’s no variance, you can’t calculate heritability)
• Genetic diversity increases —> heritability increases (closer to 1)
• Environmental diversity increases —> heritability decreases (closer to 0)
• Uses identical twins to determine number
• Important assumption: no environmental differences for identical vs fraternal twins
h 2 = 0 —> due to environment
h 2 = 1 —> due to genes
Behaviour Genetics Techniques
