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Chapter 3
Genes, Environment, and Development
• Species Heredity
• Genetic endowment
• Common to the species
• Governs maturation and aging
• Natural Selection: Genes allowing
adaptation are passed on
Evolution
• Charles Darwin (1809-1882)
• Species characteristics
• How they change over time
• Main Arguments
• Genetic variation exists in all species
• Some genes aid in adaptation
• Kettlewell’s Moths: Genetic variability
provides for adaptation
Individual Heredity - The Genetic
Code
• Zygote: union of sperm and egg
– 23 pairs of chromosomes
– Pair: One from father one from mother
• Meiosis: produces sperm and ova
• Mitosis: cell-division process
– Creates new cells
Mitosis and Meiosis Compared
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reserved.
Genes: Their Location and
Composition
Nucleus
Cell
Chromosome
Gene
DNA
The Chromosomes
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reserved.
Genes: Our Biological
Blueprint
 Chromosomes
 threadlike structures made of DNA that
contain the genes
 DNA (deoxyribonucleic acid)
 contains the genetic information that
makes up the chromosomes
 has two strands-forming a “double helix”-held together by pairs of nucleotides
Karyotype
Genes: Our Biological
Blueprint
 Genes
 biochemical units of heredity that make up
the chromosomes
 a segment of DNA synthesizes a protein
 Genome
 consisting of all the genetic material in its
chromosomes
Genetic Uniqueness &
Relatedness
•
Monozygotic (MZ) twins: 100% related
•
Dizygotic (DZ) twins: 50% on average
– 2 ova fertilized by 2 sperm
•
Siblings: 50% on average
•
Parent & Child: 50% related, shared
•
Males: XY; Females: XX
Translation of the
Genetic Code
• Genes provide instructions for
development
– Eye color and other characteristics
– Regulator genes turn on/off gene
pairs
• Adolescent growth spurt
• Shut down some in adulthood
Genotype
A genotype refers to person’s genetic heritage.
Copyright (c) 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Copyright (c) 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Epigenetic Effects on Gene
Expression
• Epigenesis
– Process through which nature and nurture coact to bring forth particular developmental
outcomes
• Epigenetic effects
– Environmental factors affect whether or not
particular genes in particular cells are expressed
– Might explain differences in identical twins
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Sickle-Cell Anemia
• Caused by hemoglobin S that reduces O2
• About 9% affected in U.S.
– Homozygous recessive (SS)
• Heterozygous: (AS) “carriers”
– Can transmit gene to offspring
Sickle-Cell Anemia
• Incomplete dominance – carriers show signs
of having recessive trait
– Will not have the disease, but sickling
episodes
• Co-dominance – neither gene in pair is
dominant or recessive
Sex-Linked Inheritance
• Single genes located on sex
chromosomes
• Actually X-linked
• Males have no counterpart on Y
chromosome
• Females have counter on second X
– Requires gene on both X’s for trait
• Hemophilia, Colorblindness
Figure 3.2
• Polygenic: Most human characteristics
influenced by multiple genes
– Height, weight, intelligence,
temperament
• Mutations: Change in
structure/arrangement of genes
– Environmental hazards (teratogens)
can cause mutations
• Down syndrome: Trisomy 21
• Intellectual disabilities
• Related to age of mother
Trisomy 21
Down Syndrome (Trisomy 21)
• Physical Deformities
flattening of the back of
the head
slanting of the eyelids
short stubby limbs
thick tongues
Figure 3.3
TURNER SYNDROME (Single X
chromosome - XO)
1/3000 females - short stature, sterile, webbed neck, stubby fingers,
arms that turn out slightly at the elbow, and a low hairline in the back
of the head
Klinefelter syndrome:
1/200 males
XXY, tall, sterile, feminine traits
FRAGILE X SYNDROME
Sex-linked: affects mostly males
eye & vision impairments
elongated face
Flat feet
Prominent ears
Mental Retardation
Autism and autistic-like behavior
Large testicles (evident after puberty)
Low muscle tone
hand biting and hand-flapping
Hyperactivity and short attention span
HUNTINGTON’S DISEASE
Single dominant gene on chromosome 4
Rapid, jerky involuntary movements
Dementia, cognitive decline, depression, occasional delusions
Hallucinations, OCD
Tay Sachs disease
–
chromosome 15
1:30 Ashkenazi
Jews carriers
Some Genetic Disorders
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Behavioral Genetics
• Genetic/environment cause of trait
• Heritability estimates (genetic)
• Methods of studying
– Experimental and selective breeding –
attempt to breed particular traits into
animals
• Tryon’s maze-bright rats
– Twin, adoption, family studies
• Reared together or apart
• Concordance rates
Figure 3.4
Estimating Influences
•
Genetic similarity
– Degree of trait similarity in family
members
•
Shared environmental influences
– Living in the same home
•
Non-shared environmental influences
– Unique experiences (e.g.,
emotionality)
Accounting for Individual
Differences
•
Correlations highest in identical twins
– Genetic factors determine trait
•
Correlations higher if twins reared
together
– Environmental factors
•
Correlations are not perfect
– Non-shared experiences
•
Identical twins more alike with age
Temperament and Personality
• Temperament – set of tendencies concerning
emotional reactivity, activity, and sociability
(genetic)
• Temperament correlations
• MZ twins = .50 to .60
• DZ twins = 0
• Personality correlations similar
• DZ shared environment unimportant
• Same home - different personalities
• Non-shared environment and genes important
Correlations from a Twin Study of the
Heritability of Angry Emotionality
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reserved.
Psychological Disorders
• Schizophrenia concordance rates
– MZ = 48%: DZ=17%
– Affected parent increases risk:
13%
• Inherited predisposition
– Environmental factors – triggers
– Prenatal exposure to infection
suspected
Gene/Environment Correlations
• Passive G/E correlations – parents’ genes
influence the environment they provide for
children, as well as the genes the child receives
• Parents create social home
• Evocative G/E correlations – child’s
genotype evokes certain reactions
• Smiley baby gets more social stimulation
• Active G/E correlations – child’s genotype
influences the environment that he/she seeks
• Child seeks parties, friends, groups, etc.
Genetic Influences on Environment
• Finding: Parents who read to their children
have brighter children. Why?
• Environment: reading to child makes
them brighter
• Genetic: brighter parents more informed
or they enjoy reading themselves
• Finding: Aggressive children have hostile
parents.
• Genetic: inherited behaviors
• Environment: growing up with negative,
hostile parents causes the behavior
Controversies Surrounding Genetic Research
• Identification of carriers of diseases
and disorders
• Giving information which leads to
abortion
• Experimenting with techniques for
genetic alteration
• Better parenting if child’s genetic
predispositions understood