I.  Evolution and species heredity

            Some identical twins share many characteristics while others are quite different

            A.  Species Heredity-- Genetic Endowment Members of a Species Have in Common

                                    Birds can fly, humans can feel guilty (but not vice versa)

            B.  Main Arguments of Darwin’s Theory

                        1.  There is genetic variation in a species

                        2.  Some genes aid in adaptation more than others do

                                    3.  Natural selection-- Genes that aid in adaptation to the environment will be

                             passed on more often than genes that do not

            C.  Kettlewell’s Study of Moths in England Demonstrate Selection Principles

                        1.  Development driven by interaction between genes and environment

            D.  Powerful Evolving Human Brain Allows Humans to Learn, Adapt, and Master


II.  Individual heredity

            Conception-- moment when egg fertilized by sperm

            A.  The Genetic Code

                        1.  Early genetic materials

                                    a.  zygote-- cell created at conception

                                    b.  chromosomes-- 46 threadlike bodies (23 pairs) containing thousands of


                                    c.  Human Genome Project government-sponsored attempt to decipher

                                         genetic code

                                                i.    mapped sequence of chemical units making up strands of DNA

                                                ii.    four basic codes A-Adenine, C-cytosine, G-guanine, T-thymine

                                                iii.   3.1 letters, with about 3-4% genes

d.      meiosis-- reproductive cell division in which one 46-chromosome

sperm or ova splits into two 23-chromosome cells

                                    e.  mitosis-- cell division producing two identical cells

                        2.  Genetic uniqueness and relatedness

                                    a.  each parent can produce more than 8 million different sperm or ova

                                    b.  crossing over-- exchanges in pairs of chromosomes before separating

                                    c.  identical twins-- one fertilized ova splits to make two genetically

                                         identical individuals child shares about 50% of genes with each parent

                                    d.  fraternal twins-- two ova released and each fertilized by different sperm

same genetic relationship as with any other sibling

                        3.  Determination of sex

                                    a.  X and Y chromosomes

                                    b.  karyotype-- photograph of the arrangement of chromosomes

                                    c.  XY is typical genetic code for male

                                    d.  XX is typical genetic code for female

            B.  Translation of the Genetic Code

                        1.  Genes responsible for production of chemical substances

                        2.  Genes influenced by biochemical environment surrounding genes and by

                             behavior of individual

                                    a.  genetic “blueprint” written in erasable pencil (not indelible ink)

                                    b.  understanding of how genes impact development not fully understood

                        3.  Genotype-- genetic makeup one inherits

                        4.  Phenotype-- actual characteristics based on genetics and environment

            C.  Mechanisms of Inheritance

                        1.  Single gene-pair inheritance

                                    a.  Gregor Mendel (a monk) pioneer in inheritance

                                    b.  dominant genes-- if even one inherited will produce the effect

                                    c.  recessive genes-- need one from both parents to produce effect

 tongue curling dominant

                                    d.  incomplete dominance-- carriers show signs of having recessive trait

                                    e.  codominance-- neither gene in pair is dominant or recessive

                        2.  Sex-linked inheritance-- trait influenced by gene on sex chromosomes

hemophilia-- genetic disorder resulting in deficiency in blood’s ability to clot

                        3.  Polygenic inheritance-- most human characteristics determined by multiple

                             genes polygenic traits-- characteristic influence by multiple pairs of genes

            D.  Mutations

                        1.  Change in one or more genes that produces new phenotype

                        2.  Environmental hazards can cause mutations

                        3.  Some mutations beneficial

sickle-cell disease-- sickle-shaped white blood cells

                                                i.    protects from affects of malaria

                                                ii.    does more harm than good in individuals living in non-malaria


            E.  Chromosome Abnormalities

                        1.  Child receives too many or too few chromosomes

                                    Down syndrome

                                                i.    trisomy 21 (three 21st chromosomes)

                                                ii.    physical and mental impact

                                                iii.   odds increase with parents age

                        2.  Sex chromosome abnormalities

                                    a.  Turner syndrome

                                                i.    female with a single X chromosome (XO)

                                                ii.    physically small, cannot reproduce, stubby fingers, lower than

                                                      average spatial and math skills

                                    b.  Klinefelter syndrome

                                                i.    male with an extra X chromosome (XXY)

                                                ii.    tall but sterile and may have feminine sex characteristics

                                    c.  Fragile X syndrome

                                                i.    most common hereditary cause of mental retardation

                                                ii.    more common in males

                                                iii.   too many repeated gene sequences

            F.  Genetic Diagnosis and Counseling

                        1.  Genetic counseling-- service assesses risk concerning potential for genetic


                        2.  Examples of disorders that can be identified via genetic counseling: cystic

                             fibrosis, hemophilia, phenylketonuria (PUK), Tay Sachs disease

                                    a.  counselors report percent probability of having a child with a disorder

                                    b.  carriers-- individual with a recessive gene that can be transmitted to

                                         offspring who do not show symptoms

                                    c.  common techniques used by counselors include ultrasound,

                                         amniocentesis, chorionic villus biopsy, preimplantation genetic

                                         diagnosis, maternal blood sampling

                                                i.    ultrasound-- visual image of fetus

                                                ii.    amniocentesis-- sample of amniotic fluid analyzed for genetic

                                                      material and other problems

                                                iii.   chorionic villus sampling-- extract hair cells from chorion

                                                      surrounding fetus and check for genetic defects

                                                iv.   preimplantation genetic diagnosis-- allow conception via in


                                                      fertilization, check DNA of first cells, impact non-defective


                                                v.  materal blood sampling-- check fetal blood cells that entered

                                                      mom via placenta

                        3.  Huntington’s disease

                                    a.  caused by single dominant gene

                                    b.  strikes in middle age and deteriorates nervous system

                                    c.  Gusella discovered location on chromosome 4

                                    d.  can be diagnosed with preimplantation genetic diagnosis


III.  Studying genetic and environmental influences

            Behavioral genetics-- study of the extent to which genetic and environmental differences

            correspond to differences in traits

            Heritability-- proportion of trait variability attributable to genes

            A.  Experimental Breeding 

Selective breeding-- attempt to breed particular traits into animals

Tyron bright and dull maze rats studies indicate that activity level,

emotion, sex drive may have genetic basis

            B.  Twin, Adoption, and Family Studies

            1.  Twins studies

                        a.  compare identical twins (share 100% of genes) raised together

                             and reared apart

b.  problem of shared environment effect in twins reared together

c.  biased toward emphasis on identifying genetic influences

            2.  Adoption study

                        a.  similar environments and different genes

                        b.  if adopted children like adoptive parents characteristic said to be due to


            3.  Family studies

                                    compare various members within family (e.g., half siblings, unrelated

                                    siblings from step families)

            C.  Estimating Influences

1.  Concordance rates-- percent of pairs if when one has trait so does other

Bailey & Pillard, homosexual concordance for identical twins 52%,

fraternal twins 22%

            2.  Correlation coefficients-- used to assess where traits vary together

            3.  Behavioral geneticists estimate impact of three factors on emotionality

a.  genes

 some support for heritability of emotionality

                        b.  shared environmental influences-- common work or home experience

weak support for influence on emotionality

c.  nonshared environmental influences-- unique experience (not shared by

other family members) support for the impact of unique experiences on emotionality

            D.  Molecular Genetics

                        Analysis of particular gene and their effect

                                    a.  collect DNA sample

                                    b.  identify multiple genes that contribute to polygenetic traits

                                                i.    many genes contribute to polygenetic effects

                                                ii.    each gene makes only a small contribution

                                                iii.   apoE4 gene linked to risk of Alzheimer’s disease

                                                iv.   environmental factors (e.g., head injury) increase risk


IV.  Accounting for individual differences

            A.  Intellectual Abilities

                        1.  Evidence for impact by genetics, shared, and nonshared environments

                        2.  Influence of genes becomes greater with age until adulthood

                                    a.  with age, IQ estimated heritability increase for identical twins

                                    b.  with age, IQ estimated heritability decrease for fraternal twins

                                    c.  biggest environmental influence are nonshared

                                    d.  IQ levels of children (including adopted children) can be improved if

                                         they are raised in a stimulating home environment early in life

            B.  Temperament and Personality

                                                            Temperament-- set of tendencies concerning emotional reactivity, activity, and


                        Siblings have different experiences of same family (and other environments)

                                    a.  living in same home does not make children more similar in personality

                                    b.  family experience lead to more differences than similarities

                                    c.  parents do not necessarily treat all children in the same manner

            C.  Psychological Disorders


                                    a.  serious mental disorder involving disturbed thinking, emotions, and

                                         social behavior

                                                                                    b.  may be genetic component to schizophrenia (predisposition for

                                                                                         developing the disorder)

                                                i.  genetic predisposition for disorder

                                                ii. having parent with schizophrenia increase in risk for disorder

            D.  The Heritability of Different Traits

                        Some traits more influenced by genes than others

                                    a.  physical and physiological traits strongly influenced by genetics

                                    b.  general intelligence moderately influenced by genetics

                                    c.  temperament and susceptibility to psychological disorders less

                                         influenced by genetics

                                    d.  some traits (e.g., creativity) uninfluenced by genetics

            E.  Influences on Heritability

                        1.  Heritability not fixed

                        2.  Heritability impact differs depending on environment

                        3.  Heritability of trait impacted by age, socioeconomic status, and other qualities


V.  Heredity and environment conspiring

            Gene’s are always turning on or off over the entire life span

            Unique genes exert themselves more as we become adults

            A.  Gene/Environment Interaction

                        1.  Expression of our genotype depends on the environment we experience, and

                             how we respond to the environment depends on our genes

                                                            2.  Caspi and colleagues described impact of genes and stressful life events on

                                                                 development of depression

                        3.  Gene-environment interaction may determine depression

                                    combination of high-risk genes and high-risk environment

            B.  Genes/Environment Correlations

                        Three kinds of gene/environment correlations

                                    people with different genes encounter different environments

                                                      i.    passive gene/environment correlations-- parents’ genes

                                                            influence  the environment they provide for children, as well as

                                                            the genes the child receives

                                                ii.    evocative gene/environment correlation-- child’s genotype

                                                      evokes certain reactions

                                                iii.   active gene/environment correlation-- child’s genotype

                                                      influences the environment that she or he seeks

            C.  Genetic Influences on the Environment

                        1.  Gene’s affect similarity of environments we experience

                                    aggression in children may be influenced by environment provided by

                                    parent and the parent’s genes

                        2.  Authors of book, The Relationship Code, argue that family processes are the

                             mechanism through which the genetic code is expressed

                                    genes and environment (especially unique experiences) conspire to shape


            D.  Controversies Surrounding Genetic Research

                        1.  While effective, genetic intervention has led to complex ethical concerns

                                    a.  test for PKU used to screen for disorder at birth

                                                with proper diet impact of PKU minimal

                                    b.  gene therapy-- substitute defective genes or alter genetic makeup

                                    i.    treatment for hemophilia and cystic fibrosis

                                    ii.    may be deadly consequences

                        2.  Great difficulty in separating out impact of genes and environment

                        3.  Genetic explanations provide little information about the translation of

                             genotypes into phenotypes