Chapter 3 Genes, Environment, and Development

Life-Span Human Development, Fifth Edition, Carol K. Sigelman and Elizabeth A. RiderChapter 3

Chapter 3

Genes, Environment, and Development


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


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 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


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


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)


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


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


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


Figure 3.2


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


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


Figure 3.3


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


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


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


Figure 3.4


Estimating Influences

• Genetic similarity

– Degree of trait similarity in family members

• Shared environmental influences

– Living in the same home

• Nonshared environmental influences

– Unique experiences


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


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


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 create social home

– Evocative G/E correlations

• Smiley baby gets more social stimulation

– Active G/E correlations

• 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

Chapter 3 Genes, Environment, and Development

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