1. Chapter 3 Genes, Environment, and Development
Chapter 3 Genes, Environment, and Development

2. Chapter 3: Genes & Environment
Chapter 3: Genes & Environment
Species Heredity
Genetic endowment
Common to the species
Governs maturation and aging
Human examples
Two eyes, sexual maturity at yrs.
Natural Selection: Genes allowing adaptation are passed on

3. Evolution
Charles Darwin ( )
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

4. Modern Evolutionary Perspectives
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

5. Individual Heredity - The Genetic Code
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

6. Genetic Uniqueness & Relatedness
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

7. Translation of the Genetic Code
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)

8. Mechanisms of Inheritance
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

9. 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

10. Sex-Linked Inheritance
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

11. Figure 3.2 The workings of sex-linked inheritance in red-green color blindness.
Figure 3.2

12. Polygenic Inheritance and Mutations
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

13. Chromosomal Abnormalities
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

14. Figure 3.3 The rate of Down syndrome births increases steeply as the mother’s age increases.
Figure 3.3

15. Sex Chromosome Abnormalities
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

16. Genetic Diagnosis and Counseling
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

17. 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

18. Figure 3.4 Correlations between the traits of identical twins raised apart in the Minnesota Twin Study.
Figure 3.4

19. Estimating Influences
Estimating Influences
Genetic similarity
Degree of trait similarity in family members
Shared environmental influences
Living in the same home
Nonshared environmental influences
Unique experiences

21. Accounting for Individual Differences
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

22. Temperament and Personality
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

23. Psychological Disorders
Psychological Disorders
Schizophrenia concordance rates
MZ = 48%: DZ=17%
Affected parent increases risk: 13%
Inherited predisposition
Environmental factors – triggers
Prenatal exposure to infection suspected

24. Gene/Environment Correlations
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.

25. Genetic Influences on Environment
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

26. Controversies Surrounding Genetic Research
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