Behavioral Genetics: The power and limits of genetic and environmental influences on behavior and personality traits Module 14

Genes: Our Codes for Life Chromosomes are long twisted strands of deoxyribonucleic acid (DNA) found in the nucleus of the cell Humans have 23 pairs of chromosomes DNA is the chemical basis of heredity and carries instructions DNA code carried on each chromosome is arranged in thousands of segments called genes. Genes are the basic unit of heredity Complex traits are formed from different combinations of genes Can be activated by environment

Expressing Genes: Dominant & Recessive Genotype—Set of genes you’re born with Phenotype—traits that are expressed/displayed (influenced by genes & environmental factors Mnemonic: Your genes (genotype) alone won’t create a phenomenal athlete or genius, you’ll need the right environment to do that (phenotype). Dominant genes—will always be expressed if present Traits such as freckles, dark eyes, dark hair, and dimples are referred to as dominant characteristics because they require only one member of a gene pair to be dominant for the trait to be displayed Recessive genes—will expressed only if paired with an identical recessive gene. Will not be expressed if paired with a dominant gene. We inherit from our biological parents a genetic potential, the expression of which can be influenced by environmental conditions.

Did you know that limb dwarfing & 6 fingers is a dominant trait?

Twin Studies Dizygotic Twins: Monozygotic Twins: Genetically no more similar than ordinary siblings Share same fetal environment Monozygotic Twins: Share 100% same genes but can have different phenotypes Differences can be attributed to: Don’t always have same copy of genes If develop in different placentas (Dizygotic) (Monozygotic)

Twin Studies & Family Influence Thomas Bouchard & the Minnesota Twins studies If trait genetic: closely related more similar than less closely related Many close relatives share environments too Types of studies to separate effects monozygotic twins reared together monozygotic twins reared apart siblings/dizygotic reared together siblings/dizygotic reared apart adoptive siblings reared together Personality characteristics does not seem to be heavily influenced by environment. Environment does impact attitudes, values, manners, faith & politics See the famous case of the Jim Twins (watch first 8 min) MSClip art Discussion here about the higher correlation between identical twins’ IQ scores than fraternal twins’ and whether siblings were reared together or apart and the genetic role then in intelligence

Nature or Nurture?

Twin Studies & IQ figure scanned in from Gray's text, pg. 370, figure 10.7

Molecular Genetics Seeks to identify specific genes that influence behavior Hope is to predict the potential of a problem and then take steps to prevent it. Ethical concerns in regards to if this is a good idea? CRISPR – Using a bacterial defense system to splice into our DNA and edit our genes.

Heritability How much of our differences/variations can be attributed to our differing genes? Refers to the variation within the group, NOT the influence of nature or nurture. Heritable trait is one that is capable of being passed down from parent to child. The more similar the environment, the more heritability can explain differences between people. The more alike the environment, the higher the percentage of heritability (likelihood their differences were caused by their genes).

Gene-Environment Interaction Genes react to the environment. - Example: nutrition affecting if you’ll reach your genetic potential for height - See Nature & Nurture: The Study of Twins (:53-4:00) – Prenatal environmental differences can have long term effects but environment can help one reach their potential. Environment acts in response to what genes have given us. - Example: good looking people are typically treated more kindly by society Who gets better treatment at a restaurant? Selection Effects – We select environments that suit our nature.

Epigenetics Epigenetics – studies how environment can trigger or block genetic expression Diet, drugs, stress affect epigenetic molecules on your DNA This explains why two identical twins could have the genetic precursor for a mental disorder but only one ends up having it. Click on this infographic for an informative link explaining Epigenetics more

Epigenetics Genes are like computer hardware. Epigenetics are like the software that runs the computer. Change the software, and you change the way the computer operates. Experiences of previous generations alter the epigenome then get passed on to the next generation where it can affect who we are. Epigenetics in Rats (3 min)