3
GENES, ENVIRONMENT, AND DEVELOPMENT
LEARNING OBJECTIVES
After students have read and studied the material in this chapter, they should be able to answer the
following questions:
1. What do species heredity and evolution contribute to our understanding of universal patterns of
development? What are the basic principles of Darwin's theory of evolution?
2. What are the modern approaches to evolution?
3. What are the basic workings of individual heredity, including the contributions of genes,
chromosomes, the zygote, and the processes of mitosis and meiosis?
4. What role do genetic factors play in the creation on twins (fraternal and identical) and the
determination of sex?
5. What is the difference between genotype and phenotype?
6. What are the three main mechanisms of inheritance? What is an example of how a child could
inherit a trait through each of the mechanisms?
7. What chromosomal abnormalities cause Down syndrome, Turner, and Klinefleter syndrome?
What symptoms do individuals with these disorders display?
8. What are genetic diagnosis and counseling? How are these issued related to Tay-Sachs and
Huntington’s disease?
9. What methods do behavioral geneticists use to assess the influences of heredity and
environment on behavioral characteristics? Describe the logic of the method, as well as
strengths weaknesses of each method.
10. How do genes and environments contribute to individual differences in intellectual ability,
temperament, and personality, and schizophrenia across the life span?
11. What type(s) of characteristics appear most strongly influenced by genetic factors? What
characteristics appear least influenced by genetics?
12. How do genes, shared environmental and nonshared environmental factors contribute to
individual differences?
17
Chapter 3
Chapter 3
18
CHAPTER OUTLINE
I.
Species heredity, evolution, and human development
Species heredity—genetic endowment members of species all share
A. Darwin's theory of evolution
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
4. Kettlewell’s study of moths in England demonstrate selection principles
5. Development driven by interaction between genes and environment
6. Powerful evolving human brain allows humans to learn, adapt, and master
7. Cultural evolution also powerful force
B. Modern evolutionary perspectives
1. Ethology-- study of the evolved behaviors of species in their natural
environments
2. Evolutionary psychology-- test implications of Darwin for human behavior
3. Seek to understand factors shaping development
4. Often focus on adaptive behavior in non human species
5. Goal of life is to ensure birth and survival of next generation
a. parental investment strategy—males investment in child rearing and
protection of small number of offspring
b. mating strategy-- multiple partners with little energy expended on child
rearing
6. Humans not evolutionary “robots” without control, but do follow biologically
adaptive behavioral patterns
7. Inborn patterns of behavior emerge only with normal genes and normal early
experience
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
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. single parent 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
19
Chapter 3
B.
C.
D.
E.
F.
Chapter 3
individuals
d. fraternal twins and siblings --Share, on average, 50% of genes
3. Determination of sex
a. X and Y chromosomes
b. karyotype-- photograph of the arrangement of chromosomes
c. XY is genetic male
d. XX is genetic female
Translation of the genetic code
1. Regulating genes -- genes responsible for turning gene pairs on or off
2. Genotype-- genetic makeup one inherits
3. Phenotype-- actual characteristics based on genetics and environment
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
d. sickle-cell disease-- recessive disorder alters shape of blood cell
e. carriers—do not have trait but can transmit to children via recessive gene
f. incomplete dominance-- carriers show signs of having recessive trait
g. codominance-- neither gene in pair dominant or recessive
2. Sex-linked inheritance-- trait influenced by gene on sex chromosomes
a. hemophilia-- genetic disorder resulting in deficiency in blood’s ability to
clot
3. Polygenic inheritance-- most human characteristics determined by multiple genes
a. polygenic traits-- characteristic influence by multiple pairs of genes
Mutations
1. Change in one or more genes that produces new phenotype
2. Environmental hazards can cause mutations
3. Cystic fibrosis
a. caused by recessive genes
b. leads to build up of sticky mucus in lungs
Chromosome abnormalities
1. Child receives too many or to few chromosomes
a. Down syndrome
i. trisomy 21
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
ii. physically small and cannot reproduce
b. Klinefelter syndrome
i. male with an extra X chromosome
ii. tall but sterile and may have feminine sex characteristics
Genetic diagnosis and counseling
20
1. Genetic counseling-- service assesses risk concerning potential for genetic
problems
2. Tay-Sachs disease
a. caused by single pair of recessive genes
b. degeneration of nervous system typically results in death in early
childhood
c. more frequent in individuals of Jewish and French Canadian ancestry
d. several methods of detecting genetic abnormalities
i. amniocentesis
ii. chorionic villus biopsy
iii. ultrasound
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 identified with genetic test
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
1. Selective breeding-- attempt to breed traits into animals
a. 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
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
a. compare various members within family
C. Estimating influences
1. Concordance rates-- percent of pairs if when one has trait so does other
2. Correlation coefficients-- used to assess where traits vary together
3. Behavioral geneticists estimate impact of three factors on emotionality
a. genes-- some support
b. shared environmental influences-- common work or home experience
i. weak support for influence on emotionality
c. nonshared environmental influences-- unique experience
i. support for the impact of unique experiences on emotionality
21
Chapter 3
IV.
Accounting for individual differences
A. Intellectual abilities
1. Evidence for influence of genetics, shared, and nonshared environments
2. Influence of genes becomes greater with age until adulthood
a. IQ estimated heritability increase from 40-50% in childhood to 80% in
adulthood
b. variation due to environment decreases from 30% in childhood to near 0
in adulthood
c. biggest environmental influence are nonshared
B. Temperament and personality
1. Temperament-- set of tendencies concerning emotional reactivity and sociability
a. Influences of individual genetic makeup and nonshared environment
b. Siblings have different experiences of same family (and other
environments)
c. living in same home does not make children more similar in personality
d. family experience lead to more differences than similarities
e. reciprocal determinism in personality—personality shaped by experiences
and experiences determined by personality
C. Psychological disorders
1. Schizophrenia
a. serious mental disorder involving disturbed thinking, emotions, and social
behavior
b. may be genetic component to schizophrenia (inherited predisposition)
c. environment may play role in schizophrenia (triggers disorder)
2. Inherit predispositions to develop some disorders
D. Heritability of different traits
1. Some traits more influenced by genes than others
2. Physical traits more influenced by genetics than psychological traits
V.
Heredity and environment conspiring
Gene’s are always turning on or off over the entire life span
Unique genes exert themselves more as become adults
A. Gene/environment interaction-- expression of our genotype depends on the environment
we experience, and how we respond to the environment depends on our genes
B. Genes/environment correlations
1. Passive correlation-- parents’ genes influence the environment they provide for
children
2. Evocative correlation-- child’s genotype evokes certain reactions
3. Active correlation-- child’s genotype influences the environment she or
he seeks
C. Genetic influences on the environment
1. Gene’s affect similarity of environments we experience
2. Authors of book, The Relationship Code, argue that family processes are the
mechanism through which the genetic code is expressed
3. Genes and environment (especially unique experiences) conspire to shape
Chapter 3
22
development
D. Controversies surrounding genetic research
1. Eugenics-- attempt to improve human race by altering genetic makeup of
population
a. sterilization
b. immigration laws
c. Nazi breeding of super race
2. Great difficulty in separating out impact of genes and environment
3. Genetic explanations provide little information about the translation of genotypes
into phenotypes
23
Chapter 3