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Chapter 3
Genes, Environment, and Development
• Species Heredity
• Genetic endowment
• Common to the species
• Governs maturation and aging
• Human examples
• Two eyes, sexual maturity at 12-14
yrs.
• 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
Modern Evolutionary Perspectives
• What we do today was adaptive for
ancestors
• Example: mothers invest more in child
rearing
• Maternity is certain; paternity may
not be
• Evolution: gene/environment interaction
• Traits are demanded by environment
• Advantageous genes for a particular
environment survive
Individual Heredity - The Genetic
Code
• Zygote: union of sperm and egg
– 23 pairs of chromosomes
– Each pair influences one characteristic
– Pair: One from father one from mother
• Meiosis: produces sperm and ova
• Mitosis: cell-division process
– Creates new cells
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
Genes: Their Location and
Composition
Nucleus
Cell
Chromosome
Gene
DNA
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
– 2 genetically identical individuals
•
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.
Phenotype
• The phenotype is one’s genotype
expressed in characteristics that can be
observed and measured.
• It includes physical traits (e.g., height,
weight) as well as psychological
characteristics (intelligence,
personality).
Copyright (c) 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Copyright (c) 2001 by The McGraw-Hill Companies, Inc. All rights reserved.
Offspring with brown eyes
Sickle-Cell Anemia
• Caused by hemoglobin S that reduces O2
• About 9% affected in U.S.
– Homozygous recessive (ss)
• Heterozygous: (Ss) “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 Inheritance and Mutations
• 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
– Produces new phenotype
– Sperm more likely than ova
– Harmful or beneficial (e.g., sickle-cell
protects from malaria)
• Errors in chromosome division:
Meiosis
• Too many or too few chromosomes
• Most spontaneously aborted
• Down syndrome: Trisomy 21
• Physical deformities (eyelid folds,
short stubby limbs, thick tongues)
• Mental retardation
• 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
Leg of X barely connected
Sex-linked: affects mostly males
eye & vision impairments
elongated face
Flat feet
High arched palate
Prominent ears
Mental Retardation
Hyper-extensible joints (double jointed)
Large testicles (evident after puberty)
Low muscle tone
Autism and autistic-like behavior
hand biting and hand-flapping
Hyperactivity and short attention span
Genetic Diagnosis and Counseling
• Tay-Sachs disease
– Cause: recessive gene pair
– European Jews/French Canadians
• Huntington’s Disease
– Single dominant gene
• Learn about risk to unborn child
• Learn about nature, inheritance and effects of
genetic disorders in family history
HUNTINGTON’S DISEASE
rapid, jerky involuntary movements
difficulty in speaking and swallowing
cognitive decline, depression, and occasionally delusions
hallucinations and obsessive compulsive disorders.
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 indicate that
activity level, emotion, sex drive may have
strong genetic basis
– 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
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
• E.g., Sociable genes
• 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