Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Chapter 3
Genes, Environment, and Development
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Chapter 3: Genes & Environment
• 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
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
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
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
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
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Individual Heredity - The Genetic Code
• Zygote: union of sperm and ovum
– 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
– Throughout life-span
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Genetic Uniqueness & Relatedness
• Monozygotic (MZ) twins: 100% related
– Single zygote divides
– 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
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
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: genetic makeup/potential
– E.g., genes for tallness
• Phenotype: actual/expressed trait (height)
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Mechanisms of Inheritance
• Single Gene-Pair Inheritance
– Dominant genes = dominant trait
• Homozygous dominant
– Recessive genes = ? Trait
• Recessive trait if paired with another
–Homozygous recessive genes
• D trait if paired with a dominant gene
–Heterozygous gene pair
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Sickle-Cell Disease
• About 9% affected in U.S.
– Homozygous recessive (ss)
• Heterozygous: (Ss) “carriers”
– Can transmit gene to offspring
• Incomplete dominance
– Will not have the disease
– May have sickling episodes
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
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, Duchene MD
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Figure 3.2
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Polygenic Inheritance and Mutations
• Polygenic: Most human characteristics
– Height, weight, intelligence, temperament
– Multiple pairs of genes
– Normally distributed
• Mutations: Change in structure/arrangement
– Produces new phenotype
– Sperm more likely than ova
– Harmful or beneficial
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Chromosomal Abnormalities
• Errors in chromosome division: Meiosis
– Too many or too few chromosomes
• Most spontaneously aborted
• Down syndrome: Trisomy 21
– Physical deformities
– Mental retardation
– Related to age of parents
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Figure 3.3
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Sex Chromosome Abnormalities
• Turner’s syndrome: 1/3000 females
– Single X chromosome (XO)
– Small, stubby fingers, sterile
• Klinefelter syndrome: 1/200 males
– XXY, tall, sterile, feminine traits
• Fragile X syndrome: mental retardation
– Leg of X barely connected
– Sex-linked: affects mostly males
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
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
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Behavioral Genetics
• Genetic/environment cause of trait
• Heritability estimates (genetic)
• Methods of studying
– Experimental and selective breeding
• Tryon’s maze-bright rats
– Twin, adoption, family studies
• Reared together or apart
• Concordance rates
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Figure 3.4
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Estimating Influences
• Genetic similarity
– Degree of trait similarity in family members
• Shared environmental influences
– Living in the same home
• Nonshared environmental influences
– Unique experiences
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
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
– Nonshared experiences
• Identical twins more alike with age
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Temperament and Personality
• Temperament correlations
– MZ twins = .50 to .60
– DZ twins = 0
• Personality correlations similar
– DZ shared environment unimportant
– Same home - different personalities
– Nonshared environment and genes
important
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Psychological Disorders
• Schizophrenia concordance rates
– MZ = 48%: DZ=17%
– Affected parent increases risk: 13%
• Inherited predisposition
– Environmental factors – triggers
– Prenatal exposure to infection suspected
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
Gene/Environment Correlations
• E.g., Sociable genes
– Passive G/E correlations
• Parents create social home
– Evocative G/E correlations
• Smiley baby gets more social stimulation
– Active G/E correlations
• Child seeks parties, friends, groups, etc.
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
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
Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. Rider
Chapter 3
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