CHAPTER OUTLINE

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

genes

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

environments

E. Chromosome Abnormalities

1. Child receives too many or too few chromosomes

Down syndrome

i. trisomy 21 (three 21^st 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

problems

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

vitro

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

cells

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

experience

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

sociability

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

Schizophrenia

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

development

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