Psychology Chapter 3 Bailey And Pillard Homosexual Concordance Rate For

Chapter 3

3

GENES, ENVIRONMENT,

AND DEVELOPMENT

LEARNING OBJECTIVES

After reading and studying the material in this chapter, the student should be able to

understand the following ideas/concepts.

3.1 EVOLUTION AND SPECIES HEREDITY

• Summarize the basic argument of Darwin’s theory of evolution and the significance of

3.2 INDIVIDUAL HEREDITY

• Describe the basics of the genetic code and what we inherit from our parents.

• Distinguish and give examples of the major mechanisms of inheritance (single gene-pair,

3.3 STUDYING GENETIC AND ENVIRONMENTAL INFLUENCES

• Define the main goal and research methods of behavioral genetics and the meaning of

3.4 SELECTED BEHAVIORAL GENETICS FINDINGS

• Summarize the main messages of behavioral genetics research on intelligence,

3.5 GENE-ENVIRONMENT INTERPLAY

Chapter 3

• Distinguish between gene-environment interaction (and the diathesis-stress and

differential susceptibility concepts) and gene-environment correlation (and passive,

CHAPTER OUTLINE

I Evolution and Species Heredity

A. Main Points of Evolution and Species Heredity

1. Virtually everyone develops in similar ways at similar ages

a. Species heredity – genetic endowment members of a species have in common

2. Main arguments of Darwin’s theory

a. There is genetic variation in a species (members of a species do not share all

3. Kettlewell’s study of moths in England demonstrates natural selection principles

a. Study of pollution and moth color

4. Cultural evolution – we “inherit” from previous generations a characteristically

Checking Mastery

1. Biological evolution will not necessarily make humans better and better over time,

but it will make them ______________.

➢ Answer: Biological evolution will make humans better adapted to the

2. For natural selection to work and for a species to evolve, what must be true of the

genetic makeup of a species?

Chapter 3

➢ Answer: For evolution to work, there must be genetic variation (some

3. What does evolutionary psychology try to explain?

➢ Answer: Evolutionary psychology tries to explain why humans think and

II Individual Heredity

A. The Genetic Code

1. Early genetic materials

a. Zygote – cell created at conception

b. Chromosomes – 46 threadlike bodies (23 pairs, one from father and one from

mother) containing the genes

c. Meiosis – reproductive cell division in which one 46-chromosome sperm or

2. The Human Genome Project

a. Federally-funded attempt to map out entire DNA sequence of all human

chromosomes using supercomputers; completed in 2003

i. 3.1 billion A, C, G, T molecules

b. Humans share majority of genes with primates

i. Some gene alleles have evolved in recent centuries (e.g., variation that

3. Genetic uniqueness and relatedness

a. Each parent can produce more than 8 million genetically different sperm or

Chapter 3

ova, and any couple could produce 64 trillion babies without having two with

identical genes

b. Crossing over – exchanges in pairs of chromosomes before separating

c. Identical twins (monozygotic) – one fertilized ovum splits to make two

4. Determination of sex

a. 22 of 23 chromosomes (autosomes) are similar in males and females

5. X vs. Y chromosome

a. X has almost 1,100 genes

b. Y has about 80 (many of which are involved in sperm production)

B. From Genotype to Phenotype

1. Genotype – genetic makeup one inherits

2. Phenotype – actual characteristics based on genetics and environment

3. Genes responsible for production of chemical substances (e.g., melanin, which

6. Fraga and colleagues analyzed expression of genes in identical twins

a. Older twin pair more genetically different from younger pairs

i. Less time spent together was predictive of more genetic variation

Chapter 3

7. No one completely understands epigenetic process (transformation of a single cell

into a living, behaving human)

C. Mechanisms of Inheritance

1. Single gene-pair inheritance – characteristic influenced by only one pair of genes

(one from mom and one from dad)

a. Gregor Mendel – nineteenth-century monk and pioneer in inheritance research

i. Noticed patterns in cross-bred strains of peas

d. Incomplete dominance – individual expresses a blend of dominant and

recessive traits

i. Child of one parent with dark skin and the other parent with light skin who

has light brown skin

e. Co-dominance – neither gene in pair is dominant or recessive

i. AB blood type is mix of A and B blood types

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

a. Most are X-linked (rather than sex-linked) as most attributes are associated

with genes on only the X chromosome

3. Polygenic inheritance – most human characteristics determined by multiple genes

4. Polygenic traits – characteristic influence by multiple pairs of genes

a. The characteristic impacted by polygenetic traits (e.g., weight, intelligence,

D. Mutations

1. Change in structure or arrangement of one or more genes that produce new

phenotype

2. Some mutations beneficial

Chapter 3

E. Copy Number Variations

1. Instances in which part of the genome is either deleted or duplicated

F. Chromosome Abnormalities

1. Child receives too many or too few chromosomes (about 1 in 160 born with more

or less than 46 chromosomes)

a. Down syndrome

i. Trisomy 21 (three 21st chromosomes)

ii. Physical (e.g., distinctive eye folds, short, stubby limbs) and mental (some

degree of intellectual disability) impact

2. Sex chromosome abnormalities

a. Turner syndrome (about 1 in 3,000 females)

i. Female with a single X chromosome (XO)

ii. Physically small, cannot reproduce, stubby fingers, lower than average

spatial and math skills

Chapter 3

G. Genetic Diseases and Their Diagnosis

1. 97% of babies are born without major birth defects/disease/disorder

a. Genetic counseling assesses risk concerning potential for genetic problems

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

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

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

b. Genetic counseling for sickle-cell disease

i. Disease causes the development of sickle-shaped blood cells that cluster

together and result in less oxygen being distributed through the circulatory

system

ii. Impacts include breathing difficulty, joint swelling and pain

3. Common prenatal screening procedures used by counselors include ultrasound,

amniocentesis, chorionic villus biopsy, maternal blood sampling, preimplantation

genetic diagnosis (Exploration Box on prenatal detection of abnormalities)

a. Ultrasound – visual image of fetus

b. Amniocentesis – sample of amniotic fluid analyzed for genetic material and

4. Huntington’s disease

a. Famous disorder associated with a single dominant gene

b. Typically strikes in middle age and deteriorates nervous system with

numerous symptoms

i. Slurred speech

Chapter 3

Checking Mastery

1. Ted and Ned, fraternal twins, are not very alike at all. Give both a “nature”

explanation and a “nurture” explanation of their differences.

➢ Answer: Nature: By the luck of the draw (which parent chromosomes end

2. Huge nose syndrome (we made it up) is caused by a single dominant gene, H. Using

diagrams such as those in Figure 3.2, figure out the odds that Herb (who has the

genotype Hh) and Harriet (who also has the genotype Hh) will have a child with huge

nose syndrome. Now repeat the exercise, but assume that huge nose syndrome is

caused by a recessive gene, h, and that both parents again have an Hh genotype.

➢ Answer: If the gene is dominant (H), 75% or three of four of the couple’s

3. Juan has red-green color blindness. Knowing that he is color blind, what can you infer

about his parents?

➢ Answer: Red–green color blindness is sex-linked and the recessive gene

III Studying Genetic and Environmental Influences

A. Basics on genetics

1. Behavioral genetics – study of the extent to which genetic and environmental

differences are responsible for a given trait

endowments

B. Experimental Breeding

1. Selective breeding – attempt to breed particular traits into animals

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

1. Twins studies

a. Compare identical twins (share 100% of genes) and fraternal twins (share an

Chapter 3

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

D. Estimating Influences

1. Concordance rates – percent of pairs in which, if when one has trait, so does the

other

a. Bailey and Pillard, homosexual concordance rate for identical twins 52%,

2. Plomin and colleagues’ behavioral geneticists estimated impact of three factors on

emotionality

a. Genes

i. Some support for heritability of emotionality

E. Molecular Genetics

1. The Human Genome Project

a. Analysis of particular genes and their effects

b. Identify how much multiple genes contribute to polygenetic traits

i. Many genes contribute to polygenetic effects

Chapter 3

Checking Mastery

1. What does the following (hypothetical) table of correlations tell you about the

contributions of genes, shared environment, and nonshared environment to frequency

of use of marijuana?

Raised together

Raised apart

Identical twins

+0.70

+0.40

Fraternal twins

+0.40

+0.10

➢ Answer: In this example, genes are important because identical twins are

more similar in frequency of marijuana use than fraternal twins; shared

2. What are two problems with adoption studies of genetic influence?

➢ Answer: Adopted children can be affected not only by their biological

3. If twin studies show that depression is heritable, what good would it do to conduct

molecular genetics studies of the disorder?

➢ Answer: Molecular genetics research can help identify which specific

VI. Selected Behavioral Genetics Findings

A. Intellectual Abilities

1. Bouchard Jr. and McGue correlated IQ scores of different pairs of relatives

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

a. Pairs of family members reared together have more similar IQ than those

reared apart

3. Influence of genes becomes greater with age until adulthood

Chapter 3

a. With age, IQ’s estimated heritability increase for identical twins

b. With age, IQ’s estimated heritability decrease for fraternal twins

B. Temperament and Personality

1. Temperament – set of tendencies concerning emotional reactivity, activity, and

sociability

a. Genes contribute to individual differences in temperament in infancy and to

2. Personality

a. About 40% of the variation on major personality dimensions is attributable to

genetic differences

b. Shared environmental influences can be important (e.g., children adopt

attitudes and interests similar to parents)

i. Parent conflict can cause multiple children in the same home to develop

C. Psychological Disorders

1. Schizophrenia – serious mental disorder involving disturbed thinking, emotions,

and social behavior

a. Genes may contribute substantially to development of the disorder

i. Average concordance rate for identical twins 48%, rate for fraternal twins

is 17%

Chapter 3

c. Do not inherit the disorder, but rather the predisposition to develop the

disorder

d. Actual development depends on combination of genetics and environmental

stress (e.g., dysfunctional family)

D. The Heritability of Different Traits

1. Some traits more influenced by genes than others

a. Observable physical (e.g., eye color, height) and physiological traits (e.g.,

reactions to alcohol) strongly influenced by genetics

E. Influences on Heritability

1. Heritability not fixed

2. Heritability impact differs depending on the age of the individuals being sampled

a. Genes explain more variation in eating disorders in girls during puberty vs.

Checking Mastery

1. Professor Gene Ohm is studying genetic and environmental influences on individual

differences in extraversion/introversion. Based on previous behavioral genetics

studies, what should he expect?

➢ Answer: Research suggests that about 40% of the variation among people

2. Ayaan’s biological mother had schizophrenia, so he was placed in an adoptive home

when he was only 2 months old. He grew up with his adoptive parents (neither of

whom had any psychological disorders) in a stable, loving family. What would you

Chapter 3

tell Ayaan, now age 18, about his chances of developing schizophrenia if you were a

genetic counselor?

➢ Answer: About 10% of children of a parent who has schizophrenia

V. Gene-Environment Interplay

A. Basic trends in genes

1. Genes are always turning on or off over the entire life span

2. Environmental influences also impact from conception to death

B. Gene-Environment Interactions

1. Genes do not determine anything but rather provide potential

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

development of depression in New Zealanders

i. Predisposition to depression results in somewhat higher probability of having

depression

C. Gene-Environment Correlations

1. Gene-environment interactions tell us that people with different genes react

differently to the experiences they have

2. Gene-environment correlations say that people with different genes experience

different environments

a. Passive gene-environment correlations – parents’ genes influence the

environment they provide for children, as well as the genes the child receives

i. Parents with “sociable genes” create a social home environment

Chapter 3

c. Active gene-environment correlation – child’s genotype influences the

environment that she or he seeks

i. Extravert likely to go to every party in sight and build a “niche” that is

D. Genetic Influences on the Environment

1. Measures of environment are heritable

2. Genes affect similarity of environments we experience and perceptions of those

environments

a. Identical twins who are irritable could help create conflict-ridden families

3. Must constantly question assumptions about nature and nurture

a. Aggression in children may be influenced by environment provided by parent

development

5. Sorting Out Genetic Influences on the Environment

a. Objective and perceived aspects of parenting

b. Time spent watching television

c. Number of stressful life events

2. Gene Therapy

Checking Mastery

Label each example below as an example of (a) gene–environment interaction, (b)

passive gene–environment correlation, (c) evocative gene–environment correlation, (d)

active gene–environment correlation, or (e) epigenetic effects.

1. Roger inherited genes for artistic creativity from his parents and grew up watching

them sketch and paint.

2. Tamara was abused as a child and this seems to have made her stress response system

overly reactive.

3. Kayla inherited genes for mathematical ability and has been taking extra math and

science courses in college.

Chapter 3

4. Sydney inherited a gene that can cause intellectual disability but only in children who

5. Jorge got genes for anxiety, and his anxious behavior makes his parents

overprotective of him.

SUGGESTIONS FOR CLASS DISCUSSIONS OR PROJECTS: To develop critical thinking

skills and enhance student learning with exercises that support the course learning objectives.

1. Sibling Trait Comparisons: Ask students to consider how they are similar to and different

from their siblings. Have them speculate about the source of these similarities and differences

(genetic factors or environmental factors). Point out that researchers argue that a shared family

environment may actually contribute more to differences than similarities among siblings.

2. Social Events and Multi-Influence Perspective: Ask students to provide examples of some

behavioral traits that they believe are primarily genetically or primarily environmentally

determined. What evidence do they have for their positions? Chances are that many will refer to

3. Sex-Linked Inheritance: Have students (possibly working in small groups) solve problems

involving single gene-pair and sex-linked inheritance by drawing tables like those in the text (see

4. Genetic Research: In the movie Spiderman, a character states, “With great power, comes

great responsibility.” In Chapter 3, students are introduced to the Human Genome Project, a

scientific endeavor that is destined to change the world as we know it (i.e., great power).

Chapter 3

Advances made by Human Genome Project researchers have also raised a variety of ethical

concerns. For example, the development of tests to identify carriers of diseases and for prenatal

detection of diseases such as cystic fibrosis and Huntington’s disease has been met with mixed