Transcript CHAPTER 3 GENES, ENVIRONMENT, AND DEVELOPMENT Learning Objective • What do evolution and species heredity contribute to our understanding of universal patterns of development?

CHAPTER 3
GENES, ENVIRONMENT, AND DEVELOPMENT
Learning Objective
• What do evolution and species heredity
contribute to our understanding of universal
patterns of development?
Species Heredity
• Genetic endowment that members of a
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species have in common
– Reason that certain patterns of
development and aging are universal
Examples
– Walk and talk around 1 year of age
– Sexual maturation from 12-14
– Wrinkling of skin in 40s and 50s
Darwin’s Theory of Evolution
• Species heredity explained by evolutionary
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theory
Main arguments of Darwin’s theory
– There is genetic variation in a species
– Some genes aid adaptation more than
others do
– Adaptive genes passed on more frequently
Evolution is about the interaction between
genes and environment
Modern Evolutionary Perspectives
• Human development influenced by a shared
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species heredity that evolved through natural
selection
Human development also influenced by
cultural evolution
– Humans inherit a characteristically human
environment and learn methods of
adapting to the environment
– Cultural evolution is based on learning and
socialization
Learning Objectives
• What are the basic elements and processes
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of individual heredity, including genes,
chromosomes, formation of a zygote, mitosis,
and meiosis?
What has the Human Genome Project
contributed to our understanding of human
development?
Individual Heredity – The Genetic Code
• Conception – new cell nucleus formed from
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genetic material of ovum and genetic material
of sperm
– New cell is the zygote
Each parent contributes 23 chromosomes, 46
total, organized into 23 pairs
– Chromosomes - threadlike bodies in
nucleus of each cell made up of genes
Individual Heredity – The Genetic Code
• Sperm and ova each have only 23
chromosomes because they are produced
through the cell division process of meiosis
– A reproductive cell (in ovary or in testis)
splits to form two 46-chromosome cells
– The two cells split again to form a total of
four cells, each of which receives 23
chromosomes
• In the female, results in three
nonfunctional cells and one ovum
• In the male, results in four sperm
Individual Heredity – The Genetic Code
• The single-cell zygote becomes a multiple-
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cell organism through the process of mitosis
– A cell (and each of its 46 chromosomes)
divides to produce two identical cells, each
containing the same 46 chromosomes
– Following conception, through mitosis, the
zygote divides into two cells, then into four
cells, then into eight cells, etc.
Mitosis continues throughout life
Individual Heredity – The Genetic Code
• Except for ova and sperm, all normal human
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cells contain copies of the 46 chromosomes
received at conception
– Both members of a chromosome pair
influence the same characteristics
Chromosomes are strands of DNA
– Deoxyribonucleic acid made up of
sequences of adenine, cytosine, guanine,
and thymine (A, C, G, and T)
– Sequences are functional units - genes
The Human Genome Project
• Researchers mapped the sequence of the
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chemical units (A,C,G, and T) that make up
the strands of DNA in a full set of human
chromosomes
Human genome consists of genes that serve
as a template for the production of particular
proteins and DNA that regulates the activity of
the protein-producing genes
999 of 1,000 base chemicals are identical;
only 1 of 1,000 accounts for human
differences
Learning Objectives
• What factors account for genetic uniqueness?
• How genetically similar are twins?
• How is sex determined?
Genetic Uniqueness and Relatedness
• Genetic uniqueness of children of same
parents due to crossing over, an aspect of
meiosis
– Before separation, pairs of chromosomes
line up; when they cross each other, parts
are exchanged
– Crossing over increases the number of
distinct sperm or ova an individual can
produce
Genetic Uniqueness and Relatedness
• Genetic similarity of parent and child
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– An individual receives half her
chromosomes and genes from her mother
and half from her father
Genetic similarity of siblings
– Siblings receive half their genes from the
same mother and half from the same
father, but meiosis determines the genes
actually received
– Siblings share half their genes, on average
Genetic Uniqueness and Relatedness
• Identical twins or monozygotic twins (or
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identical triplets, etc.)
– Genetically the same
– Result when one fertilized ovum divides to
form two or more genetically identical
individuals
Fraternal twins or dizygotic twins
– Result from release of two ova and
fertilization by two sperm
– As genetically alike as siblings
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Determination of Sex
Of the 23 pairs of chromosomes
– 22 pairs - autosomes
– 23rd pair - sex chromosomes
• In males, the 23rd pair consists of a long
chromosome (X) and a short chromosome
with fewer genes (Y)
• Females have two X chromosomes
Fathers determine a child’s sex
– If a sperm carries a Y chromosome, the XY
zygote is a genetic male
– If a sperm carries an X chromosome, the XX
zygote is a genetic female
• Caption: Chromosomes in each cell consist of
strands of DNA
Learning Objective
• How are genes translated into physical and
psychological characteristics?
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Translation and Expression
of the Genetic Code
Environmental influences combine with genetic
influences to determine how a genotype is
translated into a phenotype
– Genotype
• The genetic makeup a person inherits
– Phenotype
• The characteristics or traits that are
expressed
– Gene expression
• Activation of particular genes in particular
cells at particular times; guided by genetic
influences and affected by environmental
factors
Learning Objectives
• What are the mechanisms by which traits are
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passed from parents to offspring?
What is an example of how a child could
inherit a trait through each of these three
mechanisms?
Mechanisms of Inheritance:
Single Gene-Pair Inheritance
• Single gene-pair inheritance
– Pattern described by Gregor Mendel
– Human characteristics influenced by one
pair of genes (one from mother, one from
father)
• A dominant gene trait will be expressed
• A recessive gene trait will be expressed
only when the gene is paired with
another recessive gene for the trait
• Caption: Can you curl your tongue?
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Mechanisms of Inheritance:
Sex-Linked Inheritance
Sex-linked characteristics are influenced by
single genes located on sex chromosomes
– Actually X-linked because most attributes
are associated with genes on the X
– Y chromosomes are smaller and have
fewer genes to serve as counterpart or to
dominate
• Example: if a boy inherits a recessive
color-blindness gene on the X, there is
no color vision gene on the Y to
dominate the color-blindness gene
Mechanisms of Inheritance:
Sex-Linked Inheritance
• A female who inherits a color-blindness gene
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usually has a normal color-vision gene on her
other X chromosome that can dominate the
color-blindness gene
– If a female is to be color-blind, she must
inherit the gene on both Xs
Hemophilia is another condition that
illustrates the principles of sex-linked
inheritance
• Caption: X-linked inheritance
Mechanisms of Inheritance:
Polygenic Inheritance
• Traits such as height, weight, intelligence,
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personality, and susceptibility to cancer and
depression are polygenic
– Influenced by multiple pairs of genes
interaction with environmental factors
Many degrees of expression are possible in
polygenic traits
– Traits tend to be distributed in the
population according to the normal curve
Learning Objectives
• How do genetic mutations occur?
• How do mutations affect development?
• What are the most common chromosomal
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abnormalities?
When chromosomal abnormalities occur, how
do they affect development?
Mutations
• Mutation
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– A change in gene structure or arrangement
that produces a new phenotype
May be harmful or beneficial depending on
their nature and the environment
– Example: sickle-cell disease
Can be inherited by offspring
Chromosomal Abnormalities
• Chromosomal abnormalities occur when
there are errors in chromosome division
during meiosis
– The ovum or sperm will have too many or
too few chromosomes
– Chromosomal abnormalities are the main
source of pregnancy loss
Examples of Chromosomal Abnormalities
• Down syndrome or trisomy 21
– 21st chromosomes = 3
– Children have distinctive physical
characteristics and typically are classified
as having some degree of mental
retardation
– Associated with older age of parents
Examples of Chromosomal Abnormalities
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Chromosomal abnormalities that involve a child
receiving too few or too many sex chromosomes
– Consequence of errors in meiosis or damage
from environmental hazards
– Turner syndrome – a female born with a single
X chromosome (XO)
– Klinefelter syndrome – a male born with one or
more extra X chromosomes (XXY)
– Fragile X – one arm of the X is only barely
connected
• Caption: Photo of X chromosome with fragile
X problem
Learning Objectives
• What methods are used to screen for genetic
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abnormalities?
What are the advantages and disadvantages
of using such techniques to test for prenatal
problems?
What are some abnormalities that can
currently be detected with genetic screening?
Genetic Diagnosis and Counseling
• Genetic counseling
– A service that helps people understand
and adapt to the implications of genetic
contributions to disease
– Carriers do not have the disease but can
transmit the gene for it to their children
Issues in Genetic Diagnosis and Counseling
• Sickle-cell disease
– Sickle-shaped blood cells cluster together
and distribute less oxygen through the
circulatory system
– If parents are carriers of the recessive
gene for sickle-cell disease
• Have 25% chance of having a child with
sickle-cell disease
• Have a 50% chance of having a child
who will be a carrier
Issues in Genetic Diagnosis and Counseling
• Huntington’s disease
– Associated with a single dominant gene
– Strikes in middle age and disrupts the
nervous system
– Child of a parent with Huntington’s disease
has a 50% chance of developing the
disease
– Discovery of gene for Huntington’s on
chromosome 4 led to a test that can reveal
if a person has inherited the gene
Learning Objectives
• What methods do scientists use to discern
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the contributions of heredity and environment
to physical and psychological traits?
What are the strengths and weaknesses of
these methods?
How do scientists estimate the influences of
heredity and environment to individual
differences in traits?
How do genes, shared environment, and
nonshared environment contribute to
individual differences in traits?
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Genetic and Environmental Influences:
Behavioral Genetics
Behavioral genetics
– Study of the extent to which genetic and
environmental differences contribute to
differences in traits
– Use heritability estimates
• The proportion of all the variability in the trait
within a large sample that can be linked to
genetic differences among individuals
• Variability that is not associated with genetic
differences is associated with environmental
and experiential differences
Studying Genetic and Environmental
Influences: Experimental Breeding
• Selective breeding
– Attempting to breed animals for a particular
trait to determine whether the trait is
heritable
• Tryon bred maze-bright rats to
demonstrate the influence of genetics
upon maze-learning ability
• Other animal breeding studies showed
genetic contributions to activity level,
emotionality, aggressiveness, etc.
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Studying Genetic and Environmental
Influences: Twin, Adoption, and Family
Studies
Twin studies
– Studies of twins, both identical and
fraternal, reared apart and together
Adoption studies
– Are adopted children more similar to
biological parents or to adoptive parents?
Family studies
– Studies of siblings with different degrees of
genetic similarity and varying environments
Estimating Influences
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Concordance rates
– Statistical calculations to estimate the degree
to which heredity and environment account for
individual differences in a trait of interest
– A trait is heritable if the concordance rates are
higher for more genetically related than for
less genetically related pairs of people
Correlation coefficients
– Used when a trait (e.g., intelligence) can be
present in varying degrees
Estimating Influences
• From correlations reflecting the degree of
similarity between twins, behavioral
geneticists can estimate the contributions to
individual differences in emotionality from
– Genes
– Shared environmental influences
• Common experiences
– Nonshared environmental influences
• Experiences unique to the individual
Molecular Genetics
• Analysis of genes and their effects
– Useful in identifying the multiple genes that
contribute to polygenic traits
– Example: Alzheimer’s disease
• Twin studies show heritability but the
roles of specific genes have not been
clarified
Learning Objectives
• How do genes and environments contribute
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to individual differences in intellectual
abilities, personality and temperament, and
psychological disorders?
What do researchers mean when they talk
about the heritability of traits?
Which traits are more strongly heritable than
others?
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Findings from Behavioral Genetics
Research – IQ
Correlations highest in identical twins
– Heritability of IQ is about .50
• Genetic differences account for 50% of
variation in IQ and environmental
differences for 50%
– Genetic endowment appears to gain
importance from infancy to adulthood as a
source of individual differences in IQ
– Shared environmental differences become
less significant with age
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Findings from Behavioral Genetics
Research – Temperament and Personality
Temperament
– Tendencies to respond in predictable ways
that serve as the building blocks of personality
Buss and Plomin (1984) reported average
correlations of .50 - .60 between temperament
scores of identical twins but scores for fraternal
twins not much greater than zero
– Conclusion: living in the same home does not
generally make children more similar in
personality
– Shared environment influences are important
but nonshared influences are more important
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Findings from Behavioral Genetics
Research – Psychological Disorders
Schizophrenia
– Concordance rate for schizophrenia in
identical twin pairs is 48% and for fraternal
twins the rate is 17%
– 90% of children who have one parent with
schizophrenia do not develop schizophrenia
• This means that environmental factors
contribute significantly
– People inherit predispositions to develop
disorders, not the disorder per se
Heritability of Different Traits
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Traits that are strongly heritable include
– Physical characteristics – eye color, height,
weight
– Physiological functions – measured brain
activity, reactions to alcohol, level of physical
activity, susceptibility to certain diseases
A trait that is moderately heritable
– General intelligence
Traits that are less heritable
– Aspects of temperament and personality,
susceptibility to many psychological disorders
Influences on Heritability Estimates
• Characteristics of the sample studied
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– Age, environmental factors
Environmental factors
– Socioeconomic status
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Caption: Correlations between the traits of identical twin
raised apart in to Minnesota Twin Study
Learning Objectives
• What is an example that illustrates the
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concept of a gene-environment interaction?
What are three ways that genes and
environments correlate to influence
behavior?
What are the major controversies
surrounding genetic research?
Gene-Environment Interactions
• The effects of genes depend upon the nature
of the environment and how the individual
responds to the environment
– Often takes a combination of high-risk
genes and high-risk environment to trigger
psychological problems
Gene-Environment Correlations
• Three kinds of gene-environment correlations
– Passive – the home environment that
parents provide their children is correlated
with the children’s genotypes
– Evocative gene-environment correlations
• Child’s genotype evokes certain types of
reactions from others
– Active gene-environment correlations
• Children’s genotypes influence the kinds
of environments they seek
Genetic Influences on Environment
• Notion that people’s genes are correlated
with and possibly influence their life
experiences
– Measures of environment are heritable
• Especially family environments of
children
– Evidence that those who have closest
genetic similarity are also similar in the
environments they experience and in their
perceptions of those environments
Controversies Surrounding Genetic
Research
• Accomplishments in the study of genetics
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have led to debates about procedures, public
policy, and ethical issues
– Reproductive technology, cloning, gene
therapy, stem cell research
Some researchers may have overstated the
importance of genes and underestimated the
importance of family in development